[v4,1/2] Import CBOR library

Message ID 20231009212053.2007-2-graf@amazon.com
State New
Headers
Series Add Nitro Secure Module support |

Commit Message

Alexander Graf Oct. 9, 2023, 9:20 p.m. UTC
  To fully support the Nitro Secure Module communication protocol, we need
to encode and decode CBOR binary data. Import an MIT licensed library
from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
easily consume CBOR data.

On top of the upstream code base, I added kernel module as well as
kernel header path awareness and made checkpatch happy.

Signed-off-by: Alexander Graf <graf@amazon.com>

---

v3 -> v4:

  - New in v4
---
 MAINTAINERS                  |   8 ++
 include/linux/cbor/base.h    |  94 ++++++++++++++
 include/linux/cbor/cbor.h    |  22 ++++
 include/linux/cbor/decoder.h |  42 ++++++
 include/linux/cbor/encoder.h |  48 +++++++
 include/linux/cbor/helper.h  |  41 ++++++
 include/linux/cbor/ieee754.h |  52 ++++++++
 include/linux/cbor/parser.h  |  32 +++++
 lib/Kconfig                  |   3 +
 lib/Makefile                 |   2 +
 lib/cbor/Makefile            |  12 ++
 lib/cbor/common.c            | 105 +++++++++++++++
 lib/cbor/decoder.c           | 170 ++++++++++++++++++++++++
 lib/cbor/encoder.c           | 218 +++++++++++++++++++++++++++++++
 lib/cbor/helper.c            | 175 +++++++++++++++++++++++++
 lib/cbor/ieee754.c           | 205 +++++++++++++++++++++++++++++
 lib/cbor/parser.c            | 243 +++++++++++++++++++++++++++++++++++
 17 files changed, 1472 insertions(+)
 create mode 100644 include/linux/cbor/base.h
 create mode 100644 include/linux/cbor/cbor.h
 create mode 100644 include/linux/cbor/decoder.h
 create mode 100644 include/linux/cbor/encoder.h
 create mode 100644 include/linux/cbor/helper.h
 create mode 100644 include/linux/cbor/ieee754.h
 create mode 100644 include/linux/cbor/parser.h
 create mode 100644 lib/cbor/Makefile
 create mode 100644 lib/cbor/common.c
 create mode 100644 lib/cbor/decoder.c
 create mode 100644 lib/cbor/encoder.c
 create mode 100644 lib/cbor/helper.c
 create mode 100644 lib/cbor/ieee754.c
 create mode 100644 lib/cbor/parser.c
  

Comments

Greg KH Oct. 10, 2023, 6:13 a.m. UTC | #1
On Mon, Oct 09, 2023 at 09:20:52PM +0000, Alexander Graf wrote:
> To fully support the Nitro Secure Module communication protocol, we need
> to encode and decode CBOR binary data. Import an MIT licensed library
> from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
> easily consume CBOR data.

What is "CBOR"?  I don't see a description of it here.

And I guess you are going to keep this in sync with upstream?  Or do you
really need the full library here (you #ifdef the float stuff out), does
your module really need all of the functionality and complexity of this
library, or can it use just a much smaller one instead?

> On top of the upstream code base, I added kernel module as well as
> kernel header path awareness and made checkpatch happy.

If only the one module needs this, why not put it in the directory for
the module itself, and then when/if anyone else needs it, it could be
moved?

thanks,

greg k-h
  
Alexander Graf Oct. 10, 2023, 7:55 a.m. UTC | #2
Hey Greg,

On 10.10.23 08:13, Greg Kroah-Hartman wrote:
> On Mon, Oct 09, 2023 at 09:20:52PM +0000, Alexander Graf wrote:
>> To fully support the Nitro Secure Module communication protocol, we need
>> to encode and decode CBOR binary data. Import an MIT licensed library
>> from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
>> easily consume CBOR data.
> What is "CBOR"?  I don't see a description of it here.


CBOR is the "Concise Binary Object Representation" 
(https://en.wikipedia.org/wiki/CBOR) binary format.


>
> And I guess you are going to keep this in sync with upstream?  Or do you
> really need the full library here (you #ifdef the float stuff out), does
> your module really need all of the functionality and complexity of this
> library, or can it use just a much smaller one instead?


CBOR knows a total of 9 data types:

   - Unsigned integers
   - Signed integers
   - Binary string
   - UTF-8 string
   - Arrays
   - Maps (like a python dictionary)
   - Semantic tag
   - Bools
   - Floats

Out of these, the NSM communication protocol uses all except Semantic 
tags and Floats. The CBOR library that this patch imports does not have 
special handling for Semantic tags, which leaves only floats which are 
already #ifdef'ed out. That means there is not much to trim.

What you see here is what's needed to parse CBOR in kernel - if that's 
what we want to do. I'm happy to rip it out again and make it a pure 
user space problem to do CBOR :).


>
>> On top of the upstream code base, I added kernel module as well as
>> kernel header path awareness and made checkpatch happy.
> If only the one module needs this, why not put it in the directory for
> the module itself, and then when/if anyone else needs it, it could be
> moved?


That sounds like a great idea! Let me do that :)


Alex





Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
  
Greg KH Oct. 10, 2023, 8:03 a.m. UTC | #3
On Tue, Oct 10, 2023 at 09:55:25AM +0200, Alexander Graf wrote:
> Hey Greg,
> 
> On 10.10.23 08:13, Greg Kroah-Hartman wrote:
> > On Mon, Oct 09, 2023 at 09:20:52PM +0000, Alexander Graf wrote:
> > > To fully support the Nitro Secure Module communication protocol, we need
> > > to encode and decode CBOR binary data. Import an MIT licensed library
> > > from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
> > > easily consume CBOR data.
> > What is "CBOR"?  I don't see a description of it here.
> 
> 
> CBOR is the "Concise Binary Object Representation"
> (https://en.wikipedia.org/wiki/CBOR) binary format.
> 
> 
> > 
> > And I guess you are going to keep this in sync with upstream?  Or do you
> > really need the full library here (you #ifdef the float stuff out), does
> > your module really need all of the functionality and complexity of this
> > library, or can it use just a much smaller one instead?
> 
> 
> CBOR knows a total of 9 data types:
> 
>   - Unsigned integers
>   - Signed integers
>   - Binary string
>   - UTF-8 string
>   - Arrays
>   - Maps (like a python dictionary)
>   - Semantic tag
>   - Bools
>   - Floats
> 
> Out of these, the NSM communication protocol uses all except Semantic tags
> and Floats. The CBOR library that this patch imports does not have special
> handling for Semantic tags, which leaves only floats which are already
> #ifdef'ed out. That means there is not much to trim.
> 
> What you see here is what's needed to parse CBOR in kernel - if that's what
> we want to do. I'm happy to rip it out again and make it a pure user space
> problem to do CBOR :).

Yes, why are we parsing this in the kernel?  What could go wrong with
adding yet-another-parser in privileged context?  :)

Why does this have to be in the kernel, the data sent/recieved is over
virtio, so why does the kernel have to parse it?  I couldn't figure that
out from the driver, yet the driver seems to have a lot of hard-coded
parsing logic in it to assume specific message formats?

thanks,

greg k-h
  
Alexander Graf Oct. 10, 2023, 8:08 a.m. UTC | #4
On 10.10.23 10:03, Greg Kroah-Hartman wrote:
>
> On Tue, Oct 10, 2023 at 09:55:25AM +0200, Alexander Graf wrote:
>> Hey Greg,
>>
>> On 10.10.23 08:13, Greg Kroah-Hartman wrote:
>>> On Mon, Oct 09, 2023 at 09:20:52PM +0000, Alexander Graf wrote:
>>>> To fully support the Nitro Secure Module communication protocol, we need
>>>> to encode and decode CBOR binary data. Import an MIT licensed library
>>>> from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
>>>> easily consume CBOR data.
>>> What is "CBOR"?  I don't see a description of it here.
>>
>> CBOR is the "Concise Binary Object Representation"
>> (https://en.wikipedia.org/wiki/CBOR) binary format.
>>
>>
>>> And I guess you are going to keep this in sync with upstream?  Or do you
>>> really need the full library here (you #ifdef the float stuff out), does
>>> your module really need all of the functionality and complexity of this
>>> library, or can it use just a much smaller one instead?
>>
>> CBOR knows a total of 9 data types:
>>
>>    - Unsigned integers
>>    - Signed integers
>>    - Binary string
>>    - UTF-8 string
>>    - Arrays
>>    - Maps (like a python dictionary)
>>    - Semantic tag
>>    - Bools
>>    - Floats
>>
>> Out of these, the NSM communication protocol uses all except Semantic tags
>> and Floats. The CBOR library that this patch imports does not have special
>> handling for Semantic tags, which leaves only floats which are already
>> #ifdef'ed out. That means there is not much to trim.
>>
>> What you see here is what's needed to parse CBOR in kernel - if that's what
>> we want to do. I'm happy to rip it out again and make it a pure user space
>> problem to do CBOR :).
> Yes, why are we parsing this in the kernel?  What could go wrong with
> adding yet-another-parser in privileged context?  :)
>
> Why does this have to be in the kernel, the data sent/recieved is over
> virtio, so why does the kernel have to parse it?  I couldn't figure that
> out from the driver, yet the driver seems to have a lot of hard-coded
> parsing logic in it to assume specific message formats?


The parsing doesn't have to be in kernel and it probably shouldn't be 
either. V3 of the patch was punting all the parsing to user space, at 
which point you and Arnd said I should give it a try to do the protocol 
parsing in kernel space instead. That's why the parser is here.

If we conclude that all this in-kernel parsing is not worth it, I'm very 
happy to just go back to the the v3 ioctl interface and post v5 with 
hwrng merged into misc, but remove all CBOR logic again :)


Alex




Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
  
Greg KH Oct. 10, 2023, 8:27 a.m. UTC | #5
On Tue, Oct 10, 2023 at 10:08:43AM +0200, Alexander Graf wrote:
> 
> On 10.10.23 10:03, Greg Kroah-Hartman wrote:
> > 
> > On Tue, Oct 10, 2023 at 09:55:25AM +0200, Alexander Graf wrote:
> > > Hey Greg,
> > > 
> > > On 10.10.23 08:13, Greg Kroah-Hartman wrote:
> > > > On Mon, Oct 09, 2023 at 09:20:52PM +0000, Alexander Graf wrote:
> > > > > To fully support the Nitro Secure Module communication protocol, we need
> > > > > to encode and decode CBOR binary data. Import an MIT licensed library
> > > > > from https://github.com/libmcu/cbor (commit f3d1696f886) so that we can
> > > > > easily consume CBOR data.
> > > > What is "CBOR"?  I don't see a description of it here.
> > > 
> > > CBOR is the "Concise Binary Object Representation"
> > > (https://en.wikipedia.org/wiki/CBOR) binary format.
> > > 
> > > 
> > > > And I guess you are going to keep this in sync with upstream?  Or do you
> > > > really need the full library here (you #ifdef the float stuff out), does
> > > > your module really need all of the functionality and complexity of this
> > > > library, or can it use just a much smaller one instead?
> > > 
> > > CBOR knows a total of 9 data types:
> > > 
> > >    - Unsigned integers
> > >    - Signed integers
> > >    - Binary string
> > >    - UTF-8 string
> > >    - Arrays
> > >    - Maps (like a python dictionary)
> > >    - Semantic tag
> > >    - Bools
> > >    - Floats
> > > 
> > > Out of these, the NSM communication protocol uses all except Semantic tags
> > > and Floats. The CBOR library that this patch imports does not have special
> > > handling for Semantic tags, which leaves only floats which are already
> > > #ifdef'ed out. That means there is not much to trim.
> > > 
> > > What you see here is what's needed to parse CBOR in kernel - if that's what
> > > we want to do. I'm happy to rip it out again and make it a pure user space
> > > problem to do CBOR :).
> > Yes, why are we parsing this in the kernel?  What could go wrong with
> > adding yet-another-parser in privileged context?  :)
> > 
> > Why does this have to be in the kernel, the data sent/recieved is over
> > virtio, so why does the kernel have to parse it?  I couldn't figure that
> > out from the driver, yet the driver seems to have a lot of hard-coded
> > parsing logic in it to assume specific message formats?
> 
> 
> The parsing doesn't have to be in kernel and it probably shouldn't be
> either. V3 of the patch was punting all the parsing to user space, at which
> point you and Arnd said I should give it a try to do the protocol parsing in
> kernel space instead. That's why the parser is here.

Arnd said that, not me :)

> If we conclude that all this in-kernel parsing is not worth it, I'm very
> happy to just go back to the the v3 ioctl interface and post v5 with hwrng
> merged into misc, but remove all CBOR logic again :)

I think the less parsers we have in the kernel, the safer we are for
obvious reasons.  Unless you have a parser for this in rust?  :)

I don't really know, having a generic interface is good, but at the
expense of this api is probably not good.  individual ioctls might be
better if there are not going to be any other drivers for this type of
thing?

it's a tough call, let's see what a unified driver, no parser, looks
like, that should be pretty simple and small so maybe stick with that?

thanks,

greg k-h
  
Arnd Bergmann Oct. 11, 2023, 12:24 p.m. UTC | #6
On Tue, Oct 10, 2023, at 10:27, Greg Kroah-Hartman wrote:
> On Tue, Oct 10, 2023 at 10:08:43AM +0200, Alexander Graf wrote:
>> On 10.10.23 10:03, Greg Kroah-Hartman wrote:
>>
>> > > Out of these, the NSM communication protocol uses all except Semantic tags
>> > > and Floats. The CBOR library that this patch imports does not have special
>> > > handling for Semantic tags, which leaves only floats which are already
>> > > #ifdef'ed out. That means there is not much to trim.
>> > > 
>> > > What you see here is what's needed to parse CBOR in kernel - if that's what
>> > > we want to do. I'm happy to rip it out again and make it a pure user space
>> > > problem to do CBOR :).
>> > Yes, why are we parsing this in the kernel?  What could go wrong with
>> > adding yet-another-parser in privileged context?  :)
>> > 
>> > Why does this have to be in the kernel, the data sent/recieved is over
>> > virtio, so why does the kernel have to parse it?  I couldn't figure that
>> > out from the driver, yet the driver seems to have a lot of hard-coded
>> > parsing logic in it to assume specific message formats?
>> 
>> 
>> The parsing doesn't have to be in kernel and it probably shouldn't be
>> either. V3 of the patch was punting all the parsing to user space, at which
>> point you and Arnd said I should give it a try to do the protocol parsing in
>> kernel space instead. That's why the parser is here.
>
> Arnd said that, not me :)
>
>> If we conclude that all this in-kernel parsing is not worth it, I'm very
>> happy to just go back to the the v3 ioctl interface and post v5 with hwrng
>> merged into misc, but remove all CBOR logic again :)
>
> I think the less parsers we have in the kernel, the safer we are for
> obvious reasons.  Unless you have a parser for this in rust?  :)
>
> I don't really know, having a generic interface is good, but at the
> expense of this api is probably not good.  individual ioctls might be
> better if there are not going to be any other drivers for this type of
> thing?

I was definitely expecting something simpler than what was possible
in the v4 patch. I had another look now, and it's clear that the
ioctl interface is still not great because the variable data structures
shine through for some of the calls, and even to get to this point,
a whole lot of complexity is required underneath.

To get anything better, one would probably have to redesign the entire
interface stack (hypervisor, kernel and userland) to use regular
fixed data structures, and this seems unlikely to happen.

     Arnd
  
Greg KH Oct. 11, 2023, 5:46 p.m. UTC | #7
On Wed, Oct 11, 2023 at 02:24:48PM +0200, Arnd Bergmann wrote:
> On Tue, Oct 10, 2023, at 10:27, Greg Kroah-Hartman wrote:
> > On Tue, Oct 10, 2023 at 10:08:43AM +0200, Alexander Graf wrote:
> >> On 10.10.23 10:03, Greg Kroah-Hartman wrote:
> >>
> >> > > Out of these, the NSM communication protocol uses all except Semantic tags
> >> > > and Floats. The CBOR library that this patch imports does not have special
> >> > > handling for Semantic tags, which leaves only floats which are already
> >> > > #ifdef'ed out. That means there is not much to trim.
> >> > > 
> >> > > What you see here is what's needed to parse CBOR in kernel - if that's what
> >> > > we want to do. I'm happy to rip it out again and make it a pure user space
> >> > > problem to do CBOR :).
> >> > Yes, why are we parsing this in the kernel?  What could go wrong with
> >> > adding yet-another-parser in privileged context?  :)
> >> > 
> >> > Why does this have to be in the kernel, the data sent/recieved is over
> >> > virtio, so why does the kernel have to parse it?  I couldn't figure that
> >> > out from the driver, yet the driver seems to have a lot of hard-coded
> >> > parsing logic in it to assume specific message formats?
> >> 
> >> 
> >> The parsing doesn't have to be in kernel and it probably shouldn't be
> >> either. V3 of the patch was punting all the parsing to user space, at which
> >> point you and Arnd said I should give it a try to do the protocol parsing in
> >> kernel space instead. That's why the parser is here.
> >
> > Arnd said that, not me :)
> >
> >> If we conclude that all this in-kernel parsing is not worth it, I'm very
> >> happy to just go back to the the v3 ioctl interface and post v5 with hwrng
> >> merged into misc, but remove all CBOR logic again :)
> >
> > I think the less parsers we have in the kernel, the safer we are for
> > obvious reasons.  Unless you have a parser for this in rust?  :)
> >
> > I don't really know, having a generic interface is good, but at the
> > expense of this api is probably not good.  individual ioctls might be
> > better if there are not going to be any other drivers for this type of
> > thing?
> 
> I was definitely expecting something simpler than what was possible
> in the v4 patch. I had another look now, and it's clear that the
> ioctl interface is still not great because the variable data structures
> shine through for some of the calls, and even to get to this point,
> a whole lot of complexity is required underneath.
> 
> To get anything better, one would probably have to redesign the entire
> interface stack (hypervisor, kernel and userland) to use regular
> fixed data structures, and this seems unlikely to happen.

Why not fix this and do it properly?  What's preventing that from
happening?  We don't want to create an interface here that is broken, or
insecure, or a pain to maintain, right?

thanks,

greg k-h
  
Alexander Graf Oct. 11, 2023, 7:01 p.m. UTC | #8
On 11.10.23 19:46, Greg Kroah-Hartman wrote:
>
> On Wed, Oct 11, 2023 at 02:24:48PM +0200, Arnd Bergmann wrote:
>> On Tue, Oct 10, 2023, at 10:27, Greg Kroah-Hartman wrote:
>>> On Tue, Oct 10, 2023 at 10:08:43AM +0200, Alexander Graf wrote:
>>>> On 10.10.23 10:03, Greg Kroah-Hartman wrote:
>>>>
>>>>>> Out of these, the NSM communication protocol uses all except Semantic tags
>>>>>> and Floats. The CBOR library that this patch imports does not have special
>>>>>> handling for Semantic tags, which leaves only floats which are already
>>>>>> #ifdef'ed out. That means there is not much to trim.
>>>>>>
>>>>>> What you see here is what's needed to parse CBOR in kernel - if that's what
>>>>>> we want to do. I'm happy to rip it out again and make it a pure user space
>>>>>> problem to do CBOR :).
>>>>> Yes, why are we parsing this in the kernel?  What could go wrong with
>>>>> adding yet-another-parser in privileged context?  :)
>>>>>
>>>>> Why does this have to be in the kernel, the data sent/recieved is over
>>>>> virtio, so why does the kernel have to parse it?  I couldn't figure that
>>>>> out from the driver, yet the driver seems to have a lot of hard-coded
>>>>> parsing logic in it to assume specific message formats?
>>>>
>>>> The parsing doesn't have to be in kernel and it probably shouldn't be
>>>> either. V3 of the patch was punting all the parsing to user space, at which
>>>> point you and Arnd said I should give it a try to do the protocol parsing in
>>>> kernel space instead. That's why the parser is here.
>>> Arnd said that, not me :)
>>>
>>>> If we conclude that all this in-kernel parsing is not worth it, I'm very
>>>> happy to just go back to the the v3 ioctl interface and post v5 with hwrng
>>>> merged into misc, but remove all CBOR logic again :)
>>> I think the less parsers we have in the kernel, the safer we are for
>>> obvious reasons.  Unless you have a parser for this in rust?  :)
>>>
>>> I don't really know, having a generic interface is good, but at the
>>> expense of this api is probably not good.  individual ioctls might be
>>> better if there are not going to be any other drivers for this type of
>>> thing?
>> I was definitely expecting something simpler than what was possible
>> in the v4 patch. I had another look now, and it's clear that the
>> ioctl interface is still not great because the variable data structures
>> shine through for some of the calls, and even to get to this point,
>> a whole lot of complexity is required underneath.
>>
>> To get anything better, one would probably have to redesign the entire
>> interface stack (hypervisor, kernel and userland) to use regular
>> fixed data structures, and this seems unlikely to happen.
> Why not fix this and do it properly?  What's preventing that from
> happening?  We don't want to create an interface here that is broken, or
> insecure, or a pain to maintain, right?


The interface is neither broken, insecure nor a pain to maintain. It's 
merely not as pretty as could be. But it's there to stay because it's 
what the hypervisor has been exposing for the last 2 years.

I also frankly don't think that doing static structures is any more 
"proper" than what this interface is doing today. It's serialized data 
of variable length. That's just the nature of the beast - the backing 
data for some of these operations *is* dynamic.


Alex




Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
  
Petre Eftime Oct. 11, 2023, 8:48 p.m. UTC | #9
On Wed, Oct 11, 2023 at 8:46 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Wed, Oct 11, 2023 at 02:24:48PM +0200, Arnd Bergmann wrote:
> > On Tue, Oct 10, 2023, at 10:27, Greg Kroah-Hartman wrote:
> > > On Tue, Oct 10, 2023 at 10:08:43AM +0200, Alexander Graf wrote:
> > >> On 10.10.23 10:03, Greg Kroah-Hartman wrote:
> > >>
> > >> > > Out of these, the NSM communication protocol uses all except Semantic tags
> > >> > > and Floats. The CBOR library that this patch imports does not have special
> > >> > > handling for Semantic tags, which leaves only floats which are already
> > >> > > #ifdef'ed out. That means there is not much to trim.
> > >> > >
> > >> > > What you see here is what's needed to parse CBOR in kernel - if that's what
> > >> > > we want to do. I'm happy to rip it out again and make it a pure user space
> > >> > > problem to do CBOR :).
> > >> > Yes, why are we parsing this in the kernel?  What could go wrong with
> > >> > adding yet-another-parser in privileged context?  :)
> > >> >
> > >> > Why does this have to be in the kernel, the data sent/recieved is over
> > >> > virtio, so why does the kernel have to parse it?  I couldn't figure that
> > >> > out from the driver, yet the driver seems to have a lot of hard-coded
> > >> > parsing logic in it to assume specific message formats?
> > >>
> > >>
> > >> The parsing doesn't have to be in kernel and it probably shouldn't be
> > >> either. V3 of the patch was punting all the parsing to user space, at which
> > >> point you and Arnd said I should give it a try to do the protocol parsing in
> > >> kernel space instead. That's why the parser is here.
> > >
> > > Arnd said that, not me :)
> > >
> > >> If we conclude that all this in-kernel parsing is not worth it, I'm very
> > >> happy to just go back to the the v3 ioctl interface and post v5 with hwrng
> > >> merged into misc, but remove all CBOR logic again :)
> > >
> > > I think the less parsers we have in the kernel, the safer we are for
> > > obvious reasons.  Unless you have a parser for this in rust?  :)
> > >
> > > I don't really know, having a generic interface is good, but at the
> > > expense of this api is probably not good.  individual ioctls might be
> > > better if there are not going to be any other drivers for this type of
> > > thing?
> >
> > I was definitely expecting something simpler than what was possible
> > in the v4 patch. I had another look now, and it's clear that the
> > ioctl interface is still not great because the variable data structures
> > shine through for some of the calls, and even to get to this point,
> > a whole lot of complexity is required underneath.
> >
> > To get anything better, one would probably have to redesign the entire
> > interface stack (hypervisor, kernel and userland) to use regular
> > fixed data structures, and this seems unlikely to happen.
>
> Why not fix this and do it properly?  What's preventing that from
> happening?  We don't want to create an interface here that is broken, or
> insecure, or a pain to maintain, right?
>
> thanks,
>
> greg k-h

I would think the proposal to have fixed structures would be a
downgrade in terms of maintainability, usability and security, not an
improvement.

This current interface allows the hypervisor to extend the existing
functionality at any time, and the Linux kernel does not have to
change anything for that to work, the application does not have to be
recompiled to use the new kernel headers at any point. Adding new
APIs, adding new fields to API responses, or adding optional
parameters to the API is fully backwards compatible, would also not
require changes in userspace, as the CBOR data structures that are not
recognized can simply be skipped. This allows easy backwards
compatibility in most cases, and the userspace would be able to opt in
to new features only if it requires them, without forcing the upgrade
if it's not required.

With fixed structures, then the driver would need to be more
explicitly versioned and would need to be able to handle multiple
versions of the API at the same time, which is both more complex, less
flexible and more prone to errors.

-- epetre
  
Greg KH Oct. 11, 2023, 8:56 p.m. UTC | #10
On Wed, Oct 11, 2023 at 11:48:43PM +0300, Petre Eftime wrote:
> On Wed, Oct 11, 2023 at 8:46 PM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Wed, Oct 11, 2023 at 02:24:48PM +0200, Arnd Bergmann wrote:
> > > On Tue, Oct 10, 2023, at 10:27, Greg Kroah-Hartman wrote:
> > > > On Tue, Oct 10, 2023 at 10:08:43AM +0200, Alexander Graf wrote:
> > > >> On 10.10.23 10:03, Greg Kroah-Hartman wrote:
> > > >>
> > > >> > > Out of these, the NSM communication protocol uses all except Semantic tags
> > > >> > > and Floats. The CBOR library that this patch imports does not have special
> > > >> > > handling for Semantic tags, which leaves only floats which are already
> > > >> > > #ifdef'ed out. That means there is not much to trim.
> > > >> > >
> > > >> > > What you see here is what's needed to parse CBOR in kernel - if that's what
> > > >> > > we want to do. I'm happy to rip it out again and make it a pure user space
> > > >> > > problem to do CBOR :).
> > > >> > Yes, why are we parsing this in the kernel?  What could go wrong with
> > > >> > adding yet-another-parser in privileged context?  :)
> > > >> >
> > > >> > Why does this have to be in the kernel, the data sent/recieved is over
> > > >> > virtio, so why does the kernel have to parse it?  I couldn't figure that
> > > >> > out from the driver, yet the driver seems to have a lot of hard-coded
> > > >> > parsing logic in it to assume specific message formats?
> > > >>
> > > >>
> > > >> The parsing doesn't have to be in kernel and it probably shouldn't be
> > > >> either. V3 of the patch was punting all the parsing to user space, at which
> > > >> point you and Arnd said I should give it a try to do the protocol parsing in
> > > >> kernel space instead. That's why the parser is here.
> > > >
> > > > Arnd said that, not me :)
> > > >
> > > >> If we conclude that all this in-kernel parsing is not worth it, I'm very
> > > >> happy to just go back to the the v3 ioctl interface and post v5 with hwrng
> > > >> merged into misc, but remove all CBOR logic again :)
> > > >
> > > > I think the less parsers we have in the kernel, the safer we are for
> > > > obvious reasons.  Unless you have a parser for this in rust?  :)
> > > >
> > > > I don't really know, having a generic interface is good, but at the
> > > > expense of this api is probably not good.  individual ioctls might be
> > > > better if there are not going to be any other drivers for this type of
> > > > thing?
> > >
> > > I was definitely expecting something simpler than what was possible
> > > in the v4 patch. I had another look now, and it's clear that the
> > > ioctl interface is still not great because the variable data structures
> > > shine through for some of the calls, and even to get to this point,
> > > a whole lot of complexity is required underneath.
> > >
> > > To get anything better, one would probably have to redesign the entire
> > > interface stack (hypervisor, kernel and userland) to use regular
> > > fixed data structures, and this seems unlikely to happen.
> >
> > Why not fix this and do it properly?  What's preventing that from
> > happening?  We don't want to create an interface here that is broken, or
> > insecure, or a pain to maintain, right?
> >
> > thanks,
> >
> > greg k-h
> 
> I would think the proposal to have fixed structures would be a
> downgrade in terms of maintainability, usability and security, not an
> improvement.
> 
> This current interface allows the hypervisor to extend the existing
> functionality at any time, and the Linux kernel does not have to
> change anything for that to work, the application does not have to be
> recompiled to use the new kernel headers at any point. Adding new
> APIs, adding new fields to API responses, or adding optional
> parameters to the API is fully backwards compatible, would also not
> require changes in userspace, as the CBOR data structures that are not
> recognized can simply be skipped. This allows easy backwards
> compatibility in most cases, and the userspace would be able to opt in
> to new features only if it requires them, without forcing the upgrade
> if it's not required.
> 
> With fixed structures, then the driver would need to be more
> explicitly versioned and would need to be able to handle multiple
> versions of the API at the same time, which is both more complex, less
> flexible and more prone to errors.

Yes, but you are trading off the complexity of adding
yet-another-protocol-parser to the kernel vs. making a strict
user/kernel api, right?

Which one is correct?  Can you verify that this parser really is correct
and doesn't have any overflows/security issues in it?  I can't, maybe
someone needs to write it in rust :)

thanks,

greg k-h
  

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 6c4cce45a09d..5c23081ede95 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4661,6 +4661,14 @@  S:	Odd Fixes
 F:	Documentation/devicetree/bindings/arm/cavium-thunder2.txt
 F:	arch/arm64/boot/dts/cavium/thunder2-99xx*
 
+CBOR LIBRARY
+M:	Alexander Graf <graf@amazon.com>
+L:	linux-kernel@vger.kernel.org
+L:	The AWS Nitro Enclaves Team <aws-nitro-enclaves-devel@amazon.com>
+S:	Supported
+F:	include/linux/cbor/
+F:	lib/cbor/
+
 CBS/ETF/TAPRIO QDISCS
 M:	Vinicius Costa Gomes <vinicius.gomes@intel.com>
 L:	netdev@vger.kernel.org
diff --git a/include/linux/cbor/base.h b/include/linux/cbor/base.h
new file mode 100644
index 000000000000..db15fb834b4f
--- /dev/null
+++ b/include/linux/cbor/base.h
@@ -0,0 +1,94 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_BASE_H
+#define CBOR_BASE_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/stddef.h>
+#include <linux/types.h>
+
+#if !defined(CBOR_RECURSION_MAX_LEVEL)
+#define CBOR_RECURSION_MAX_LEVEL		8
+#endif
+
+#define CBOR_INDEFINITE_VALUE			(-1)
+#define CBOR_RESERVED_VALUE			(-2)
+
+#define CBOR_ADDITIONAL_INFO_MASK		0x1fu /* the low-order 5 bits */
+#define get_cbor_major_type(data_item)		((data_item) >> 5)
+#define get_cbor_additional_info(major_type)	\
+	((major_type) & CBOR_ADDITIONAL_INFO_MASK)
+
+typedef enum {
+	CBOR_SUCCESS, /**< well-formed */
+	CBOR_ILLEGAL, /**< not well-formed */
+	CBOR_INVALID, /**< well-formed but invalid */
+	CBOR_OVERRUN, /**< more items than given buffer space */
+	CBOR_BREAK,
+	CBOR_EXCESSIVE, /**< recursion more than @ref CBOR_RECURSION_MAX_LEVEL */
+} cbor_error_t;
+
+typedef enum {
+	CBOR_ITEM_UNKNOWN,
+	CBOR_ITEM_INTEGER, /**< unsigned integer and negative integer */
+	CBOR_ITEM_STRING, /**< byte string and text string */
+	CBOR_ITEM_ARRAY,
+	CBOR_ITEM_MAP,
+	CBOR_ITEM_FLOAT,
+	CBOR_ITEM_SIMPLE_VALUE,
+} cbor_item_data_t;
+
+typedef struct {
+	cbor_item_data_t type;
+	size_t offset;
+	size_t size; /**< either of the length of value in bytes or the number
+		       of items in case of container type */
+} cbor_item_t;
+
+typedef struct {
+	uint8_t const *msg;
+	size_t msgsize;
+	size_t msgidx;
+
+	cbor_item_t *items;
+	size_t itemidx;
+	size_t maxitems;
+} cbor_reader_t;
+
+typedef struct {
+	uint8_t *buf;
+	size_t bufsize;
+	size_t bufidx;
+} cbor_writer_t;
+
+/**
+ * Initialize the reader for CBOR encoded messages.
+ *
+ * @param[in,out] reader reader context for the actual encoded message
+ * @param[out] items a pointer to item buffers
+ * @param[in] maxitems the maximum number of items to be stored in @p items
+ */
+void cbor_reader_init(cbor_reader_t *reader, cbor_item_t *items, size_t maxitems);
+void cbor_writer_init(cbor_writer_t *writer, void *buf, size_t bufsize);
+size_t cbor_writer_len(cbor_writer_t const *writer);
+uint8_t const *cbor_writer_get_encoded(cbor_writer_t const *writer);
+
+cbor_item_data_t cbor_get_item_type(cbor_item_t const *item);
+size_t cbor_get_item_size(cbor_item_t const *item);
+
+uint8_t cbor_get_following_bytes(uint8_t additional_info);
+
+size_t cbor_copy(uint8_t *dst, uint8_t const *src, size_t len);
+size_t cbor_copy_be(uint8_t *dst, uint8_t const *src, size_t len);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_BASE_H */
diff --git a/include/linux/cbor/cbor.h b/include/linux/cbor/cbor.h
new file mode 100644
index 000000000000..92d69ac7ae40
--- /dev/null
+++ b/include/linux/cbor/cbor.h
@@ -0,0 +1,22 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_H
+#define CBOR_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/cbor/parser.h>
+#include <linux/cbor/decoder.h>
+#include <linux/cbor/encoder.h>
+#include <linux/cbor/helper.h>
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_H */
diff --git a/include/linux/cbor/decoder.h b/include/linux/cbor/decoder.h
new file mode 100644
index 000000000000..846f0d215662
--- /dev/null
+++ b/include/linux/cbor/decoder.h
@@ -0,0 +1,42 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_DECODER_H
+#define CBOR_DECODER_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/cbor/base.h>
+
+/**
+ * Decode a CBOR data item
+ *
+ * @param[in] reader reader context for the actual encoded message
+ * @param[in] item meta data about the item to be decoded
+ * @param[out] buf the buffer where decoded value to be written in
+ * @param[in] bufsize the buffer size
+ *
+ * @return a code of @ref cbor_error_t
+ */
+cbor_error_t cbor_decode(cbor_reader_t const *reader, cbor_item_t const *item,
+		void *buf, size_t bufsize);
+/**
+ * Get the pointer to an item value
+ *
+ * @param[in] reader reader context for the actual encoded message
+ * @param[in] item meta data about the item to be decoded
+ *
+ * @return the pointer to the item value
+ */
+void const *cbor_decode_pointer(cbor_reader_t const *reader,
+		cbor_item_t const *item);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_DECODER_H */
diff --git a/include/linux/cbor/encoder.h b/include/linux/cbor/encoder.h
new file mode 100644
index 000000000000..360568825454
--- /dev/null
+++ b/include/linux/cbor/encoder.h
@@ -0,0 +1,48 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_ENCODER_H
+#define CBOR_ENCODER_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/cbor/base.h>
+
+cbor_error_t cbor_encode_unsigned_integer(cbor_writer_t *writer, uint64_t value);
+cbor_error_t cbor_encode_negative_integer(cbor_writer_t *writer, int64_t value);
+
+cbor_error_t cbor_encode_byte_string(cbor_writer_t *writer,
+		uint8_t const *data, size_t datasize);
+cbor_error_t cbor_encode_byte_string_indefinite(cbor_writer_t *writer);
+
+cbor_error_t cbor_encode_text_string(cbor_writer_t *writer,
+		char const *text, size_t textsize);
+cbor_error_t cbor_encode_null_terminated_text_string(cbor_writer_t *writer,
+		char const *text);
+cbor_error_t cbor_encode_text_string_indefinite(cbor_writer_t *writer);
+
+cbor_error_t cbor_encode_array(cbor_writer_t *writer, size_t length);
+cbor_error_t cbor_encode_array_indefinite(cbor_writer_t *writer);
+
+cbor_error_t cbor_encode_map(cbor_writer_t *writer, size_t length);
+cbor_error_t cbor_encode_map_indefinite(cbor_writer_t *writer);
+
+cbor_error_t cbor_encode_break(cbor_writer_t *writer);
+
+cbor_error_t cbor_encode_simple(cbor_writer_t *writer, uint8_t value);
+cbor_error_t cbor_encode_bool(cbor_writer_t *writer, bool value);
+cbor_error_t cbor_encode_null(cbor_writer_t *writer);
+cbor_error_t cbor_encode_undefined(cbor_writer_t *writer);
+
+cbor_error_t cbor_encode_float(cbor_writer_t *writer, float value);
+cbor_error_t cbor_encode_double(cbor_writer_t *writer, double value);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_ENCODER_H */
diff --git a/include/linux/cbor/helper.h b/include/linux/cbor/helper.h
new file mode 100644
index 000000000000..d366583d2c54
--- /dev/null
+++ b/include/linux/cbor/helper.h
@@ -0,0 +1,41 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_HELPER_H
+#define CBOR_HELPER_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/cbor/base.h>
+
+struct cbor_parser {
+	const void *key;
+	size_t keylen;
+	void (*run)(const cbor_reader_t *reader,
+			const struct cbor_parser *parser,
+			const cbor_item_t *item, void *arg);
+};
+
+bool cbor_unmarshal(cbor_reader_t *reader,
+		const struct cbor_parser *parsers, size_t nr_parsers,
+		const void *msg, size_t msglen, void *arg);
+
+size_t cbor_iterate(const cbor_reader_t *reader,
+		    const cbor_item_t *parent,
+		    void (*callback_each)(const cbor_reader_t *reader,
+			    const cbor_item_t *item, const cbor_item_t *parent,
+			    void *arg),
+		    void *arg);
+
+const char *cbor_stringify_error(cbor_error_t err);
+const char *cbor_stringify_item(cbor_item_t *item);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_HELPER_H */
diff --git a/include/linux/cbor/ieee754.h b/include/linux/cbor/ieee754.h
new file mode 100644
index 000000000000..1362f3774d7c
--- /dev/null
+++ b/include/linux/cbor/ieee754.h
@@ -0,0 +1,52 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_IEEE754_H
+#define CBOR_IEEE754_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/cbor/base.h>
+
+typedef union {
+	uint16_t value;
+	struct {
+		uint32_t m: 10;
+		uint32_t e: 5;
+		uint32_t sign: 1;
+	} components;
+} ieee754_half_t;
+
+typedef union {
+	float value;
+	struct {
+		uint32_t m: 23;
+		uint32_t e: 8;
+		uint32_t sign: 1;
+	} components;
+} ieee754_single_t;
+
+typedef union {
+	double value;
+	struct {
+		uint64_t m: 52;
+		uint64_t e: 11;
+		uint64_t sign: 1;
+	} components;
+} ieee754_double_t;
+
+uint16_t ieee754_convert_single_to_half(float value);
+double ieee754_convert_half_to_double(uint16_t value);
+
+bool ieee754_is_shrinkable_to_half(float value);
+bool ieee754_is_shrinkable_to_single(double value);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_IEEE754_H */
diff --git a/include/linux/cbor/parser.h b/include/linux/cbor/parser.h
new file mode 100644
index 000000000000..554004799f0a
--- /dev/null
+++ b/include/linux/cbor/parser.h
@@ -0,0 +1,32 @@ 
+/* SPDX-License-Identifier: MIT */
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#ifndef CBOR_PARSER_H
+#define CBOR_PARSER_H
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+#include <linux/cbor/base.h>
+
+/**
+ * Parse the encoded CBOR messages into items.
+ *
+ * @param[in,out] reader reader context for the actual encoded message
+ * @param[in] msg CBOR encoded message
+ * @param[in] msgsize the @p msg size in bytes
+ * @param[out] nitems_parsed the number of items parsed gets stored if not null
+ *
+ * @return a code of @ref cbor_error_t
+ */
+cbor_error_t cbor_parse(cbor_reader_t *reader, void const *msg, size_t msgsize,
+		size_t *nitems_parsed);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif /* CBOR_PARSER_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index c686f4adc124..12fb3d68cd9a 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -764,3 +764,6 @@  config ASN1_ENCODER
 
 config POLYNOMIAL
        tristate
+
+config CBOR
+	tristate
diff --git a/lib/Makefile b/lib/Makefile
index 740109b6e2c8..287f3dcaff31 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -317,6 +317,8 @@  obj-$(CONFIG_ASN1_ENCODER) += asn1_encoder.o
 
 obj-$(CONFIG_FONT_SUPPORT) += fonts/
 
+obj-$(CONFIG_CBOR) += cbor/
+
 hostprogs	:= gen_crc32table
 hostprogs	+= gen_crc64table
 clean-files	:= crc32table.h
diff --git a/lib/cbor/Makefile b/lib/cbor/Makefile
new file mode 100644
index 000000000000..6b090ae0f4a8
--- /dev/null
+++ b/lib/cbor/Makefile
@@ -0,0 +1,12 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_CBOR) += cbor.o
+
+cbor-y := \
+	common.o \
+	decoder.o \
+	encoder.o \
+	helper.o \
+	parser.o \
+
+cbor-$(CONFIG_CBOR_FLOAT) += ieee754.o
diff --git a/lib/cbor/common.c b/lib/cbor/common.c
new file mode 100644
index 000000000000..a4677a9bc0a3
--- /dev/null
+++ b/lib/cbor/common.c
@@ -0,0 +1,105 @@ 
+// SPDX-License-Identifier: MIT
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#include <linux/cbor/base.h>
+#include <linux/module.h>
+
+#if !defined(assert)
+#define assert(expr)
+#endif
+
+static size_t copy_le(uint8_t *dst, uint8_t const *src, size_t len)
+{
+	for (size_t i = 0; i < len; i++)
+		dst[len - i - 1] = src[i];
+
+	return len;
+}
+
+static size_t copy_be(uint8_t *dst, uint8_t const *src, size_t len)
+{
+	for (size_t i = 0; i < len; i++)
+		dst[i] = src[i];
+
+	return len;
+}
+
+size_t cbor_copy(uint8_t *dst, uint8_t const *src, size_t len)
+{
+#if defined(CBOR_BIG_ENDIAN)
+	return copy_be(dst, src, len);
+#else
+	return copy_le(dst, src, len);
+#endif
+}
+EXPORT_SYMBOL_GPL(cbor_copy);
+
+size_t cbor_copy_be(uint8_t *dst, uint8_t const *src, size_t len)
+{
+	return copy_be(dst, src, len);
+}
+EXPORT_SYMBOL_GPL(cbor_copy_be);
+
+uint8_t cbor_get_following_bytes(uint8_t additional_info)
+{
+	if (additional_info < 24)
+		return 0;
+	else if (additional_info == 31)
+		return (uint8_t)CBOR_INDEFINITE_VALUE;
+	else if (additional_info >= 28)
+		return (uint8_t)CBOR_RESERVED_VALUE;
+
+	return (uint8_t)(1u << (additional_info - 24));
+}
+EXPORT_SYMBOL_GPL(cbor_get_following_bytes);
+
+cbor_item_data_t cbor_get_item_type(cbor_item_t const *item)
+{
+	return item->type;
+}
+EXPORT_SYMBOL_GPL(cbor_get_item_type);
+
+size_t cbor_get_item_size(cbor_item_t const *item)
+{
+	return item->size;
+}
+EXPORT_SYMBOL_GPL(cbor_get_item_size);
+
+void cbor_reader_init(cbor_reader_t *reader, cbor_item_t *items, size_t maxitems)
+{
+	assert(reader != NULL);
+
+	reader->items = items;
+	reader->maxitems = maxitems;
+	reader->itemidx = 0;
+}
+EXPORT_SYMBOL_GPL(cbor_reader_init);
+
+void cbor_writer_init(cbor_writer_t *writer, void *buf, size_t bufsize)
+{
+	assert(writer != NULL);
+	assert(buf != NULL);
+
+	writer->buf = (uint8_t *)buf;
+	writer->bufsize = bufsize;
+	writer->bufidx = 0;
+}
+EXPORT_SYMBOL_GPL(cbor_writer_init);
+
+size_t cbor_writer_len(cbor_writer_t const *writer)
+{
+	return writer->bufidx;
+}
+EXPORT_SYMBOL_GPL(cbor_writer_len);
+
+uint8_t const *cbor_writer_get_encoded(cbor_writer_t const *writer)
+{
+	return (uint8_t const *)writer->buf;
+}
+EXPORT_SYMBOL_GPL(cbor_writer_get_encoded);
+
+MODULE_DESCRIPTION("CBOR helper functions");
+MODULE_AUTHOR("Kyunghwan Kwon");
+MODULE_LICENSE("GPL");
diff --git a/lib/cbor/decoder.c b/lib/cbor/decoder.c
new file mode 100644
index 000000000000..1ec0b17ecf6c
--- /dev/null
+++ b/lib/cbor/decoder.c
@@ -0,0 +1,170 @@ 
+// SPDX-License-Identifier: MIT
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#include <linux/cbor/decoder.h>
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/module.h>
+
+#if !defined(MIN)
+#define MIN(a, b)				(((a) > (b)) ? (b) : (a))
+#endif
+
+typedef cbor_error_t (*item_decoder_t)(cbor_item_t const *item,
+		uint8_t const *msg, uint8_t *buf, size_t bufsize);
+
+static cbor_error_t decode_pass(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize);
+static cbor_error_t decode_integer(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize);
+static cbor_error_t decode_string(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize);
+static cbor_error_t decode_float(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize);
+static cbor_error_t decode_simple(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize);
+
+static const item_decoder_t decoders[] = {
+	decode_pass,		/* 0: CBOR_ITEM_UNKNOWN */
+	decode_integer,		/* 1: CBOR_ITEM_INTEGER */
+	decode_string,		/* 2: CBOR_ITEM_STRING */
+	decode_pass,		/* 3: CBOR_ITEM_ARRAY */
+	decode_pass,		/* 4: CBOR_ITEM_MAP */
+	decode_float,		/* 5: CBOR_ITEM_FLOAT */
+	decode_simple,		/* 6: CBOR_ITEM_SIMPLE_VALUE */
+};
+
+static uint8_t get_simple_value(uint8_t val)
+{
+	switch (val) {
+	case 20: /* false */
+		return 0;
+	case 21: /* true */
+		return 1;
+	case 22: /* null */
+		return '\0';
+	case 23: /* undefined */
+	default:
+		return val;
+	}
+}
+
+static bool is_break(cbor_item_t const *item)
+{
+	return item->type == CBOR_ITEM_FLOAT && item->size == 0xff;
+}
+
+static cbor_error_t decode_unsigned_integer(cbor_item_t const *item,
+		uint8_t const *msg, uint8_t *buf, size_t bufsize)
+{
+	uint8_t additional_info = get_cbor_additional_info(msg[item->offset]);
+	uint8_t following_bytes = cbor_get_following_bytes(additional_info);
+
+	if (following_bytes == 0)
+		buf[0] = additional_info;
+
+	cbor_copy(buf, &msg[item->offset + 1], following_bytes);
+
+	(void)bufsize;
+	return CBOR_SUCCESS;
+}
+
+static cbor_error_t decode_negative_integer(cbor_item_t const *item,
+		uint8_t const *msg, uint8_t *buf, size_t bufsize)
+{
+	cbor_error_t err = decode_unsigned_integer(item, msg, buf, bufsize);
+
+	if (err != CBOR_SUCCESS)
+		return err;
+
+	uint64_t val = 0;
+	size_t len = item->size ? item->size : 1;
+
+	cbor_copy_be((uint8_t *)&val, buf, len);
+
+	val = ~val;
+
+	/*
+	 * The value becomes a positive one if the data type size of the
+	 * variable is larger than the value size. So we set MSB first here to
+	 * keep it negative.
+	 */
+	for (uint8_t i = 0; i < MIN(bufsize, 8u); i++)
+		buf[i] = 0xff;
+
+	cbor_copy_be(buf, (uint8_t *)&val, len);
+
+	return CBOR_SUCCESS;
+}
+
+static cbor_error_t decode_integer(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize)
+{
+	switch (get_cbor_major_type(msg[item->offset])) {
+	case 0: /* unsigned integer */
+		return decode_unsigned_integer(item, msg, buf, bufsize);
+	case 1: /* negative integer */
+		return decode_negative_integer(item, msg, buf, bufsize);
+	default:
+		return CBOR_ILLEGAL;
+	}
+}
+
+static cbor_error_t decode_string(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize)
+{
+	for (size_t i = 0; i < item->size; i++)
+		buf[i] = msg[item->offset + i];
+
+	(void)bufsize;
+	return CBOR_SUCCESS;
+}
+
+static cbor_error_t decode_float(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize)
+{
+	return decode_unsigned_integer(item, msg, buf, bufsize);
+}
+
+static cbor_error_t decode_simple(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize)
+{
+	cbor_error_t err = decode_unsigned_integer(item, msg, buf, bufsize);
+
+	buf[0] = get_simple_value(buf[0]);
+
+	return err;
+}
+
+static cbor_error_t decode_pass(cbor_item_t const *item, uint8_t const *msg,
+		uint8_t *buf, size_t bufsize)
+{
+	(void)item;
+	(void)msg;
+	(void)buf;
+	(void)bufsize;
+	return CBOR_SUCCESS;
+}
+
+void const *cbor_decode_pointer(cbor_reader_t const *reader,
+		cbor_item_t const *item)
+{
+	return &reader->msg[item->offset];
+}
+EXPORT_SYMBOL_GPL(cbor_decode_pointer);
+
+cbor_error_t cbor_decode(cbor_reader_t const *reader, cbor_item_t const *item,
+		void *buf, size_t bufsize)
+{
+	if (is_break(item))
+		return CBOR_BREAK;
+	if (item->size > bufsize || bufsize == 0 || buf == NULL)
+		return CBOR_OVERRUN;
+
+	memset(buf, 0, bufsize);
+
+	return decoders[item->type](item, reader->msg, (uint8_t *)buf, bufsize);
+}
+EXPORT_SYMBOL_GPL(cbor_decode);
diff --git a/lib/cbor/encoder.c b/lib/cbor/encoder.c
new file mode 100644
index 000000000000..9b3f8ac8f670
--- /dev/null
+++ b/lib/cbor/encoder.c
@@ -0,0 +1,218 @@ 
+// SPDX-License-Identifier: MIT
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#include <linux/cbor/encoder.h>
+#include <linux/string.h>
+#include <linux/module.h>
+
+#ifdef CONFIG_CBOR_FLOAT
+#include <linux/cbor/ieee754.h>
+#endif
+
+#define MAJOR_TYPE_BIT			5
+
+#if !defined(MIN)
+#define MIN(a, b)			(((a) > (b)) ? (b) : (a))
+#endif
+
+static uint8_t get_additional_info(uint64_t value)
+{
+	uint8_t additional_info = 0;
+
+	if (value & ~(0x100000000ull - 1)) /* 8-byte following */
+		additional_info = 27;
+	else if (value & ~(0x10000ull - 1)) /* 4-byte following */
+		additional_info = 26;
+	else if (value & ~(0x100ull - 1)) /* 2-byte following */
+		additional_info = 25;
+	else if (value >= 24) /* 1-byte following */
+		additional_info = 24;
+	else /* 0 ~ 23 */
+		additional_info = (uint8_t)value;
+
+	return additional_info;
+}
+
+static cbor_error_t encode_core(cbor_writer_t *writer, uint8_t major_type,
+		uint8_t const *data, uint64_t datasize, bool indefinite)
+{
+	uint8_t *buf = &writer->buf[writer->bufidx];
+	uint8_t additional_info = get_additional_info(datasize);
+	uint8_t following_bytes = cbor_get_following_bytes(additional_info);
+
+	if (indefinite) {
+		additional_info = 31;
+		following_bytes = 0;
+	}
+
+	size_t bytes_to_write = (size_t)datasize + following_bytes + 1;
+	/*
+	 * NOTE: if not string, `datasize` is the actual value to be written.
+	 * And the `following_bytes` is the length of it.
+	 */
+	if (!(major_type == 2 || major_type == 3))
+		bytes_to_write -= (size_t)datasize;
+
+	if (bytes_to_write > (writer->bufsize - writer->bufidx))
+		return CBOR_OVERRUN;
+
+	buf[0] = (uint8_t)(major_type << MAJOR_TYPE_BIT) | additional_info;
+	cbor_copy(&buf[1], (uint8_t const *)&datasize, following_bytes);
+	if (data != NULL)
+		cbor_copy_be(&buf[1 + following_bytes], data, (size_t)datasize);
+
+	writer->bufidx += bytes_to_write;
+
+	return CBOR_SUCCESS;
+}
+
+static cbor_error_t encode_simple(cbor_writer_t *writer, uint8_t value)
+{
+	return encode_core(writer, 7, NULL, value, false);
+}
+
+cbor_error_t cbor_encode_unsigned_integer(cbor_writer_t *writer, uint64_t value)
+{
+	return encode_core(writer, 0, NULL, value, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_unsigned_integer);
+
+cbor_error_t cbor_encode_negative_integer(cbor_writer_t *writer, int64_t value)
+{
+	return encode_core(writer, 1, NULL, ((uint64_t)-value) - 1, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_negative_integer);
+
+cbor_error_t cbor_encode_byte_string(cbor_writer_t *writer,
+		uint8_t const *data, size_t datasize)
+{
+	return encode_core(writer, 2, data, datasize, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_byte_string);
+
+cbor_error_t cbor_encode_byte_string_indefinite(cbor_writer_t *writer)
+{
+	return encode_core(writer, 2, NULL, 0, true);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_byte_string_indefinite);
+
+
+cbor_error_t cbor_encode_text_string(cbor_writer_t *writer,
+		char const *text, size_t textsize)
+{
+	return encode_core(writer, 3,
+			(uint8_t const *)text, textsize, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_text_string);
+
+cbor_error_t cbor_encode_null_terminated_text_string(cbor_writer_t *writer,
+		char const *text)
+{
+	size_t len = 0;
+
+	if (text != NULL)
+		len = MIN(strlen(text), writer->bufsize - writer->bufidx);
+
+	return encode_core(writer, 3, (uint8_t const *)text, len, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_null_terminated_text_string);
+
+cbor_error_t cbor_encode_array(cbor_writer_t *writer, size_t length)
+{
+	return encode_core(writer, 4, NULL, length, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_array);
+
+cbor_error_t cbor_encode_array_indefinite(cbor_writer_t *writer)
+{
+	return encode_core(writer, 4, NULL, 0, true);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_array_indefinite);
+
+cbor_error_t cbor_encode_map(cbor_writer_t *writer, size_t length)
+{
+	return encode_core(writer, 5, NULL, length, false);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_map);
+
+cbor_error_t cbor_encode_map_indefinite(cbor_writer_t *writer)
+{
+	return encode_core(writer, 5, NULL, 0, true);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_map_indefinite);
+
+cbor_error_t cbor_encode_break(cbor_writer_t *writer)
+{
+	return encode_core(writer, 7, NULL, 0xff, true);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_break);
+
+cbor_error_t cbor_encode_simple(cbor_writer_t *writer, uint8_t value)
+{
+	return encode_simple(writer, value);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_simple);
+
+cbor_error_t cbor_encode_bool(cbor_writer_t *writer, bool value)
+{
+	return encode_simple(writer, (uint8_t)(value + 20));
+}
+EXPORT_SYMBOL_GPL(cbor_encode_bool);
+
+cbor_error_t cbor_encode_null(cbor_writer_t *writer)
+{
+	return encode_simple(writer, 22);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_null);
+
+cbor_error_t cbor_encode_undefined(cbor_writer_t *writer)
+{
+	return encode_simple(writer, 23);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_undefined);
+
+#ifdef CONFIG_CBOR_FLOAT
+static cbor_error_t encode_float(cbor_writer_t *writer, float value)
+{
+	if (ieee754_is_shrinkable_to_half(value)) {
+		uint16_t half = ieee754_convert_single_to_half(value);
+
+		writer->buf[writer->bufidx++] = 0xF9;
+		writer->bufidx += cbor_copy(&writer->buf[writer->bufidx],
+				(uint8_t const *)&half, sizeof(half));
+
+		return CBOR_SUCCESS;
+	}
+
+	writer->buf[writer->bufidx++] = 0xFA;
+	writer->bufidx += cbor_copy(&writer->buf[writer->bufidx],
+			(uint8_t const *)&value, sizeof(value));
+
+	return CBOR_SUCCESS;
+}
+
+cbor_error_t cbor_encode_float(cbor_writer_t *writer, float value)
+{
+	return encode_float(writer, value);
+}
+
+cbor_error_t cbor_encode_double(cbor_writer_t *writer, double value)
+{
+	if (ieee754_is_shrinkable_to_single(value))
+		return encode_float(writer, (float)value);
+
+	writer->buf[writer->bufidx++] = 0xFB;
+	writer->bufidx += cbor_copy(&writer->buf[writer->bufidx],
+			(uint8_t const *)&value, sizeof(value));
+
+	return CBOR_SUCCESS;
+}
+#endif
+
+cbor_error_t cbor_encode_text_string_indefinite(cbor_writer_t *writer)
+{
+	return encode_core(writer, 3, NULL, 0, true);
+}
+EXPORT_SYMBOL_GPL(cbor_encode_text_string_indefinite);
diff --git a/lib/cbor/helper.c b/lib/cbor/helper.c
new file mode 100644
index 000000000000..f7b3e7deea67
--- /dev/null
+++ b/lib/cbor/helper.c
@@ -0,0 +1,175 @@ 
+// SPDX-License-Identifier: MIT
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#include <linux/cbor/helper.h>
+#include <linux/cbor/parser.h>
+#include <linux/cbor/decoder.h>
+
+#include <linux/string.h>
+#include <linux/module.h>
+
+struct parser_ctx {
+	const struct cbor_parser *parsers;
+	size_t nr_parsers;
+	void *arg;
+};
+
+static const struct cbor_parser *get_parser(const struct parser_ctx *ctx,
+		intptr_t intkey, const void *strkey, size_t strkey_len)
+{
+	for (size_t i = 0; i < ctx->nr_parsers; i++) {
+		const struct cbor_parser *p = &ctx->parsers[i];
+
+		if (!p->key)
+			continue;
+
+		if (strkey && strkey_len && p->keylen >= strkey_len) {
+			if (memcmp(p->key, strkey, strkey_len) == 0)
+				return p;
+		} else if (intkey == (intptr_t)p->key) {
+			return p;
+		}
+	}
+
+	return NULL;
+}
+
+static void parse_item(const cbor_reader_t *reader, const cbor_item_t *item,
+		    const cbor_item_t *parent, void *arg)
+{
+	struct parser_ctx *ctx = (struct parser_ctx *)arg;
+	const void *strkey = NULL;
+	size_t strkey_len = 0;
+	intptr_t intkey = -1;
+
+	if (parent && parent->type == CBOR_ITEM_MAP) {
+		if ((item - parent) % 2) { /* key */
+			return;
+		}
+
+		if ((item-1)->type == CBOR_ITEM_INTEGER) {
+			cbor_decode(reader, item-1, &intkey, sizeof(intkey));
+		} else {
+			strkey = cbor_decode_pointer(reader, item-1);
+			strkey_len = (item-1)->size;
+		}
+	}
+
+	if (strkey || intkey != -1) {
+		const struct cbor_parser *parser = get_parser(ctx,
+				intkey, strkey, strkey_len);
+
+		if (parser && parser->run)
+			parser->run(reader, parser, item, ctx->arg);
+	}
+}
+
+static size_t iterate_each(const cbor_reader_t *reader,
+		    const cbor_item_t *items, size_t nr_items,
+		    const cbor_item_t *parent,
+		    void (*callback_each)(const cbor_reader_t *reader,
+			    const cbor_item_t *item, const cbor_item_t *parent,
+			    void *arg),
+		    void *arg)
+{
+	size_t offset = 0;
+	size_t i = 0;
+
+	for (i = 0; i < nr_items; i++) {
+		const cbor_item_t *item = &items[i+offset];
+
+		if (item->type == CBOR_ITEM_MAP
+				|| item->type == CBOR_ITEM_ARRAY) {
+			size_t len = item->type == CBOR_ITEM_MAP ?
+					item->size*2 : item->size;
+			offset += iterate_each(reader, item+1, len, item,
+					callback_each, arg);
+			continue;
+		}
+
+		if (cbor_decode(reader, item, 0, 0) == CBOR_BREAK)
+			break;
+
+		(*callback_each)(reader, item, parent, arg);
+	}
+
+	return i + offset;
+}
+
+bool cbor_unmarshal(cbor_reader_t *reader,
+		const struct cbor_parser *parsers, size_t nr_parsers,
+		const void *msg, size_t msglen, void *arg)
+{
+	size_t n;
+	cbor_error_t err = cbor_parse(reader, msg, msglen, &n);
+
+	if (err != CBOR_SUCCESS && err != CBOR_BREAK)
+		return false;
+
+	struct parser_ctx ctx = {
+		.parsers = parsers,
+		.nr_parsers = nr_parsers,
+		.arg = arg,
+	};
+
+	iterate_each(reader, reader->items, n, 0, parse_item, &ctx);
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(cbor_unmarshal);
+
+size_t cbor_iterate(const cbor_reader_t *reader,
+		    const cbor_item_t *parent,
+		    void (*callback_each)(const cbor_reader_t *reader,
+			    const cbor_item_t *item, const cbor_item_t *parent,
+			    void *arg),
+		    void *arg)
+{
+	return iterate_each(reader, reader->items, reader->itemidx,
+			parent, callback_each, arg);
+}
+EXPORT_SYMBOL_GPL(cbor_iterate);
+
+const char *cbor_stringify_error(cbor_error_t err)
+{
+	switch (err) {
+	case CBOR_SUCCESS:
+		return "success";
+	case CBOR_INVALID:
+		return "invalid";
+	case CBOR_OVERRUN:
+		return "out of memory";
+	case CBOR_BREAK:
+		return "break";
+	case CBOR_EXCESSIVE:
+		return "too deep recursion";
+	case CBOR_ILLEGAL:
+	default:
+		return "not well-formed";
+	}
+}
+EXPORT_SYMBOL_GPL(cbor_stringify_error);
+
+const char *cbor_stringify_item(cbor_item_t *item)
+{
+	switch (item->type) {
+	case CBOR_ITEM_INTEGER:
+		return "integer";
+	case CBOR_ITEM_STRING:
+		return "string";
+	case CBOR_ITEM_ARRAY:
+		return "array";
+	case CBOR_ITEM_MAP:
+		return "map";
+	case CBOR_ITEM_FLOAT:
+		return "float";
+	case CBOR_ITEM_SIMPLE_VALUE:
+		return "simple value";
+	case CBOR_ITEM_UNKNOWN:
+	default:
+		return "unknown";
+	}
+}
+EXPORT_SYMBOL_GPL(cbor_stringify_item);
diff --git a/lib/cbor/ieee754.c b/lib/cbor/ieee754.c
new file mode 100644
index 000000000000..acf180a99f01
--- /dev/null
+++ b/lib/cbor/ieee754.c
@@ -0,0 +1,205 @@ 
+// SPDX-License-Identifier: MIT
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+/*
+ * | precision | sign | exponent | mantissa | bias |   exp range  |
+ * | --------- | ---- | -------- | -------- | ---- | ------------ |
+ * | half      | 1    |  5       | 10       |   15 |   -14 ~   15 |
+ * | single    | 1    |  8       | 23       |  127 |  -126 ~  127 |
+ * | double    | 1    | 11       | 52       | 1023 | -1022 ~ 1023 |
+ *
+ * ## Special cases
+ * | s |   e  | m  |     desc.     |
+ * | - | -----| -- | ------------- |
+ * | 0 |    0 |  0 | +0.0          |
+ * | 1 |    0 |  0 | -0.0          |
+ * | 0 |    0 | !0 | 0.m * 2^-126  |
+ * | 1 |    0 | !0 | -0.m * 2^-126 |
+ * | 0 | 0xff |  0 | infinity      |
+ * | 1 | 0xff |  0 | -infinity     |
+ * | X | 0xff | -1 | Quiet NaN     |
+ * | X | 0xff | !0 | Signaling NaN |
+ *
+ * ## Terms
+ * - f: source bias
+ * - t: target bias
+ * - e: exponent
+ * - m: mantissa
+ */
+
+#include <linux/cbor/ieee754.h>
+
+#define BIAS_HALF				15
+#define BIAS_SINGLE				127
+#define BIAS_DOUBLE				1023
+
+#define E_MASK_HALF				((1u << 5) - 1)
+#define E_MASK_SINGLE				((1ul << 8) - 1)
+#define E_MASK_DOUBLE				((1ul << 11) - 1)
+
+#define M_BIT_HALF				10
+#define M_BIT_SINGLE				23
+#define M_BIT_DOUBLE				52
+
+#define M_MASK_HALF				((1u << M_BIT_HALF) - 1)
+#define M_MASK_SINGLE				((1ul << M_BIT_SINGLE) - 1)
+#define M_MASK_DOUBLE				((1ull << M_BIT_DOUBLE) - 1)
+
+static int find_last_set_bit(unsigned int value)
+{
+	int cnt = 0;
+
+	while (value != 0) {
+		value >>= 1;
+		cnt++;
+	}
+
+	return cnt;
+}
+
+static bool is_over_range(unsigned int e, unsigned int f, unsigned int t)
+{
+	return e > (f + t);
+}
+
+static bool is_under_range(unsigned int e, unsigned int f, unsigned int t)
+{
+	return e < (f - t + 1);
+}
+
+static bool is_in_range(unsigned int e, unsigned int f, unsigned int t)
+{
+	return !is_over_range(e, f, t) && !is_under_range(e, f, t);
+}
+
+static bool is_in_subrange(unsigned int e, unsigned int target_m_bits,
+		unsigned int f, unsigned int t)
+{
+	return is_under_range(e, f, t) && ((f - e - t) < target_m_bits);
+}
+
+static bool is_precision_lost(uint64_t m, unsigned int f, unsigned int t)
+{
+	return (m & ((1ull << (f - t)) - 1)) != 0;
+}
+
+uint16_t ieee754_convert_single_to_half(float value)
+{
+	ieee754_single_t single = { .value = value };
+	ieee754_half_t half = { .value = 0 };
+	uint8_t exp = M_BIT_SINGLE - M_BIT_HALF;
+
+	half.components.sign = single.components.sign;
+	if (single.components.e == E_MASK_SINGLE) { /* NaN or infinity */
+		half.components.e = E_MASK_HALF;
+	} else if (is_over_range(single.components.e, BIAS_SINGLE, BIAS_HALF)) {
+		/* make it NaN */
+		half.components.e = E_MASK_HALF;
+		single.components.m = 0;
+	} else if (is_under_range(single.components.e, BIAS_SINGLE, BIAS_HALF)) {
+		/* expand the exponent to the mantissa to make it subnormal */
+		exp = (uint8_t)(exp + ((BIAS_SINGLE - single.components.e) - BIAS_HALF));
+		single.components.m = M_MASK_SINGLE;
+	} else { /* zero, normal */
+		if (single.components.e != 0) {
+			half.components.e = (uint8_t)(single.components.e
+				- BIAS_SINGLE + BIAS_HALF) & E_MASK_HALF;
+		}
+	}
+
+	/* precision may be lost discarding outrange lower bits */
+	half.components.m = ((uint32_t)single.components.m >> exp) & M_MASK_HALF;
+
+	return half.value;
+}
+
+double ieee754_convert_half_to_double(uint16_t value)
+{
+	ieee754_half_t half = { .value = value };
+	ieee754_double_t d;
+
+	d.components.sign = half.components.sign;
+	d.components.e = half.components.e;
+	d.components.m = half.components.m;
+
+	if (half.components.e == E_MASK_HALF) { /* NaN or infinity */
+		d.components.e = E_MASK_DOUBLE;
+		if (half.components.m == M_MASK_HALF) /* Quiet NaN */
+			d.components.m = M_MASK_DOUBLE;
+		else if (half.components.m != 0) /* Signaling NaN */
+			d.components.m = (1ull << (M_BIT_DOUBLE - 1));
+	} else if (half.components.e == 0) { /* zero or subnormal */
+		if (half.components.m != 0) { /* subnormal */
+			/* find the leading 1 to nomalize */
+			uint64_t leading_shift = (uint64_t)(M_BIT_HALF -
+					find_last_set_bit(half.components.m) + 1);
+			d.components.m <<= leading_shift;
+			d.components.e =
+				(BIAS_DOUBLE - BIAS_HALF - leading_shift + 1)
+				& E_MASK_DOUBLE;
+		}
+	} else { /* normal */
+		d.components.e = (uint32_t)(BIAS_DOUBLE + (half.components.e
+					- BIAS_HALF)) & 0x7FFu/*11-bit*/;
+	}
+
+	d.components.m <<= M_BIT_DOUBLE - M_BIT_HALF;
+
+	return d.value;
+}
+
+bool ieee754_is_shrinkable_to_half(float value)
+{
+	ieee754_single_t single = { .value = value };
+
+	if (single.components.e == 0) {
+		if (single.components.m == 0) { /* zero */
+			return true;
+		}
+		/* subnormal */
+		if (!is_precision_lost(single.components.m,
+					M_BIT_SINGLE, M_BIT_HALF)) {
+			return true;
+		}
+	} else if (single.components.e == E_MASK_SINGLE) { /* NaN or infinity */
+		return true;
+	} else if (is_in_range(single.components.e, BIAS_SINGLE, BIAS_HALF) &&
+			!is_precision_lost(single.components.m, M_BIT_SINGLE,
+				M_BIT_HALF)) {
+		return true;
+	} else if (is_in_subrange(single.components.e, M_BIT_HALF,
+				BIAS_SINGLE, BIAS_HALF)) {
+		return true;
+	}
+
+	return false;
+}
+
+bool ieee754_is_shrinkable_to_single(double value)
+{
+	ieee754_double_t d = { .value = value };
+
+	if (d.components.e == 0) {
+		if (d.components.m == 0) { /* zero */
+			return true;
+		}
+		/* subnormal */
+		if (!is_precision_lost(d.components.m,
+					M_BIT_DOUBLE, M_BIT_SINGLE)) {
+			return true;
+		}
+	} else if (d.components.e == E_MASK_DOUBLE) { /* NaN or infinity */
+		return true;
+	} else if (is_in_range(d.components.e, BIAS_DOUBLE, BIAS_SINGLE) &&
+			!is_precision_lost(d.components.m, M_BIT_DOUBLE,
+				M_BIT_SINGLE)) {
+		return true;
+	} else if (is_in_subrange(d.components.e, M_BIT_SINGLE,
+				BIAS_DOUBLE, BIAS_SINGLE)) {
+		return true;
+	}
+
+	return false;
+}
diff --git a/lib/cbor/parser.c b/lib/cbor/parser.c
new file mode 100644
index 000000000000..c997834f7c48
--- /dev/null
+++ b/lib/cbor/parser.c
@@ -0,0 +1,243 @@ 
+// SPDX-License-Identifier: MIT
+/*
+ * SPDX-FileCopyrightText: 2021 Kyunghwan Kwon <k@mononn.com>
+ */
+
+#include <linux/cbor/parser.h>
+#include <linux/module.h>
+
+#if !defined(assert)
+#define assert(expr)
+#endif
+
+struct parser_context {
+	cbor_reader_t *reader;
+
+	uint8_t major_type;
+	uint8_t additional_info;
+	uint8_t following_bytes;
+
+	uint8_t recursion_depth;
+
+	_Static_assert(CBOR_RECURSION_MAX_LEVEL < 256, "");
+};
+
+typedef cbor_error_t (*type_parser_t)(struct parser_context *ctx);
+
+static cbor_error_t do_integer(struct parser_context *ctx);
+static cbor_error_t do_string(struct parser_context *ctx);
+static cbor_error_t do_recursive(struct parser_context *ctx);
+static cbor_error_t do_tag(struct parser_context *ctx);
+static cbor_error_t do_float_and_other(struct parser_context *ctx);
+
+/* 8 parsers for 3-bit major type */
+static const type_parser_t parsers[] = {
+	do_integer,		/* 0: unsigned integer */
+	do_integer,		/* 1: negative integer */
+	do_string,		/* 2: byte string */
+	do_string,		/* 3: text string encoded as utf-8 */
+	do_recursive,		/* 4: array */
+	do_recursive,		/* 5: map */
+	do_tag,			/* 6: tag */
+	do_float_and_other,	/* 7: float, simple value, and break */
+};
+
+static bool has_valid_following_bytes(const struct parser_context *ctx,
+		cbor_error_t *err)
+{
+	*err = CBOR_SUCCESS;
+
+	if (ctx->following_bytes == (uint8_t)CBOR_RESERVED_VALUE) {
+		*err = CBOR_ILLEGAL;
+		return false;
+	} else if (ctx->following_bytes == (uint8_t)CBOR_INDEFINITE_VALUE) {
+		return true;
+	}
+
+	if ((ctx->following_bytes + 1u)
+			> ctx->reader->msgsize - ctx->reader->msgidx) {
+		*err = CBOR_ILLEGAL;
+		return false;
+	}
+
+	return true;
+}
+
+static size_t go_get_item_length(struct parser_context *ctx)
+{
+	uint64_t len = 0;
+	size_t offset = 0;
+
+	if (ctx->following_bytes == (uint8_t)CBOR_INDEFINITE_VALUE) {
+		len = (uint64_t)CBOR_INDEFINITE_VALUE;
+	} else if (ctx->following_bytes == 0) {
+		len = ctx->additional_info;
+	} else {
+		const uint8_t *msg = &ctx->reader->msg[ctx->reader->msgidx];
+
+		cbor_copy((uint8_t *)&len, &msg[1], ctx->following_bytes);
+		offset = ctx->following_bytes;
+	}
+
+	ctx->reader->msgidx += offset + 1;
+
+	return (size_t)len;
+}
+
+static cbor_error_t parse(struct parser_context *ctx, size_t maxitems)
+{
+	cbor_error_t err = CBOR_SUCCESS;
+
+	if (++ctx->recursion_depth > CBOR_RECURSION_MAX_LEVEL)
+		return CBOR_EXCESSIVE;
+
+	for (size_t i = 0; i < maxitems &&
+			ctx->reader->itemidx < ctx->reader->maxitems &&
+			ctx->reader->msgidx < ctx->reader->msgsize; i++) {
+		uint8_t val = ctx->reader->msg[ctx->reader->msgidx];
+
+		ctx->major_type = get_cbor_major_type(val);
+		ctx->additional_info = get_cbor_additional_info(val);
+		ctx->following_bytes =
+			cbor_get_following_bytes(ctx->additional_info);
+
+		if (!has_valid_following_bytes(ctx, &err))
+			break;
+
+		err = parsers[ctx->major_type](ctx);
+
+		if (err == CBOR_BREAK) {
+			if ((maxitems == (size_t)CBOR_INDEFINITE_VALUE) ||
+					(ctx->reader->msgidx ==
+						ctx->reader->msgsize)) {
+				break;
+			}
+		} else if (err != CBOR_SUCCESS) {
+			break;
+		}
+
+		err = CBOR_SUCCESS;
+	}
+
+	ctx->recursion_depth--;
+
+	assert(ctx->msgidx <= ctx->msgsize);
+
+	return err;
+}
+
+static cbor_error_t do_integer(struct parser_context *ctx)
+{
+	if (ctx->following_bytes == (uint8_t)CBOR_INDEFINITE_VALUE)
+		return CBOR_ILLEGAL;
+
+	cbor_item_t *item = &ctx->reader->items[ctx->reader->itemidx];
+
+	item->type = CBOR_ITEM_INTEGER;
+	item->size = (size_t)ctx->following_bytes;
+	item->offset = ctx->reader->msgidx;
+
+	ctx->reader->msgidx += (size_t)(ctx->following_bytes + 1);
+	ctx->reader->itemidx++;
+
+	return CBOR_SUCCESS;
+}
+
+static cbor_error_t do_string(struct parser_context *ctx)
+{
+	cbor_item_t *item = &ctx->reader->items[ctx->reader->itemidx];
+	size_t len = go_get_item_length(ctx);
+
+	item->type = CBOR_ITEM_STRING;
+	item->size = len;
+	item->offset = ctx->reader->msgidx;
+
+	if (len == (size_t)CBOR_INDEFINITE_VALUE) {
+		ctx->reader->itemidx++;
+		return parse(ctx, ctx->reader->maxitems - ctx->reader->itemidx);
+	}
+	if (len > ctx->reader->msgsize - ctx->reader->msgidx)
+		return CBOR_ILLEGAL;
+
+	ctx->reader->msgidx += len;
+	ctx->reader->itemidx++;
+
+	return CBOR_SUCCESS;
+}
+
+static cbor_error_t do_recursive(struct parser_context *ctx)
+{
+	size_t current_item_index = ctx->reader->itemidx;
+	cbor_item_t *item = &ctx->reader->items[current_item_index];
+	size_t len = go_get_item_length(ctx);
+
+	item->type = (cbor_item_data_t)(ctx->major_type - 1);
+	item->offset = ctx->reader->msgidx;
+	item->size = len;
+	if (len != (size_t)CBOR_INDEFINITE_VALUE &&
+			len > ctx->reader->msgsize - ctx->reader->msgidx) {
+		return CBOR_ILLEGAL;
+	}
+
+	ctx->reader->itemidx++;
+
+	return parse(ctx, len);
+}
+
+/* TODO: Implement tag */
+static cbor_error_t do_tag(struct parser_context *ctx)
+{
+	(void)ctx;
+	return CBOR_INVALID;
+}
+
+static cbor_error_t do_float_and_other(struct parser_context *ctx)
+{
+	cbor_item_t *item = &ctx->reader->items[ctx->reader->itemidx];
+	cbor_error_t err = CBOR_SUCCESS;
+
+	item->type = CBOR_ITEM_FLOAT;
+	item->size = (size_t)ctx->following_bytes;
+	item->offset = ctx->reader->msgidx;
+
+	if (ctx->following_bytes == (uint8_t)CBOR_INDEFINITE_VALUE) {
+		ctx->reader->msgidx++;
+		ctx->reader->itemidx++;
+		return CBOR_BREAK;
+	} else if (!has_valid_following_bytes(ctx, &err)) {
+		return err;
+	} else if (ctx->following_bytes <= 1) {
+		item->type = CBOR_ITEM_SIMPLE_VALUE;
+	}
+
+	ctx->reader->msgidx += item->size + 1;
+	ctx->reader->itemidx++;
+
+	return err;
+}
+
+cbor_error_t cbor_parse(cbor_reader_t *reader, void const *msg, size_t msgsize,
+		size_t *nitems_parsed)
+{
+	assert(reader->items != NULL);
+	reader->itemidx = 0;
+
+	reader->msg = (uint8_t const *)msg;
+	reader->msgsize = msgsize;
+	reader->msgidx = 0;
+
+	struct parser_context ctx = {
+		.reader = reader,
+	};
+
+	cbor_error_t err = parse(&ctx, reader->maxitems);
+
+	if (err == CBOR_SUCCESS && reader->msgidx < reader->msgsize)
+		err = CBOR_OVERRUN;
+
+	if (nitems_parsed != NULL)
+		*nitems_parsed = reader->itemidx;
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(cbor_parse);