diff mbox series

[v4,1/2] kexec: Support purgatories with .text.hot sections

Message ID 20230321-kexec_clang16-v4-1-1340518f98e9@chromium.org
State New
Headers
Series kexec: Fix kexec_file_load for llvm16 |

Commit Message

Ricardo Ribalda March 27, 2023, 3:06 p.m. UTC 
  Clang16 links the purgatory text in two sections:

  [ 1] .text             PROGBITS         0000000000000000  00000040
       00000000000011a1  0000000000000000  AX       0     0     16
  [ 2] .rela.text        RELA             0000000000000000  00003498
       0000000000000648  0000000000000018   I      24     1     8
  ...
  [17] .text.hot.        PROGBITS         0000000000000000  00003220
       000000000000020b  0000000000000000  AX       0     0     1
  [18] .rela.text.hot.   RELA             0000000000000000  00004428
       0000000000000078  0000000000000018   I      24    17     8

And both of them have their range [sh_addr ... sh_addr+sh_size] on the
area pointed by `e_entry`.

This causes that image->start is calculated twice, once for .text and
another time for .text.hot. The second calculation leaves image->start
in a random location.

Because of this, the system crashes inmediatly after:

kexec_core: Starting new kernel

Cc: stable@vger.kernel.org
Reviewed-by: Ross Zwisler <zwisler@google.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 kernel/kexec_file.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

Comments

Simon Horman March 30, 2023, 7:48 a.m. UTC | #1 
On Mon, Mar 27, 2023 at 05:06:53PM +0200, Ricardo Ribalda wrote:
> Clang16 links the purgatory text in two sections:
> 
>   [ 1] .text             PROGBITS         0000000000000000  00000040
>        00000000000011a1  0000000000000000  AX       0     0     16
>   [ 2] .rela.text        RELA             0000000000000000  00003498
>        0000000000000648  0000000000000018   I      24     1     8
>   ...
>   [17] .text.hot.        PROGBITS         0000000000000000  00003220
>        000000000000020b  0000000000000000  AX       0     0     1
>   [18] .rela.text.hot.   RELA             0000000000000000  00004428
>        0000000000000078  0000000000000018   I      24    17     8
> 
> And both of them have their range [sh_addr ... sh_addr+sh_size] on the
> area pointed by `e_entry`.
> 
> This causes that image->start is calculated twice, once for .text and
> another time for .text.hot. The second calculation leaves image->start
> in a random location.
> 
> Because of this, the system crashes inmediatly after:

s/inmediatly/immediately/

> 
> kexec_core: Starting new kernel
> 
> Cc: stable@vger.kernel.org

Maybe a fixes tag is warranted here.

> Reviewed-by: Ross Zwisler <zwisler@google.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  kernel/kexec_file.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index f1a0e4e3fb5c..25a37d8f113a 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -901,10 +901,21 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
>  		}
>  
>  		offset = ALIGN(offset, align);
> +
> +		/*
> +		 * Check if the segment contains the entry point, if so,
> +		 * calculate the value of image->start based on it.
> +		 * If the compiler has produced more than one .text sections

nit: s/sections/section/

> +		 * (Eg: .text.hot), they are generally after the main .text

If this is the general case, then are there cases where this doesn't hold?

> +		 * section, and they shall not be used to calculate
> +		 * image->start. So do not re-calculate image->start if it
> +		 * is not set to the initial value.
> +		 */
>  		if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
>  		    pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
>  		    pi->ehdr->e_entry < (sechdrs[i].sh_addr
> -					 + sechdrs[i].sh_size)) {
> +					 + sechdrs[i].sh_size) &&
> +		    kbuf->image->start == pi->ehdr->e_entry) {
>  			kbuf->image->start -= sechdrs[i].sh_addr;
>  			kbuf->image->start += kbuf->mem + offset;
>  		}
> 
> -- 
> 2.40.0.348.gf938b09366-goog-b4-0.11.0-dev-696ae
> 
> _______________________________________________
> kexec mailing list
> kexec@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
>
Ricardo Ribalda March 30, 2023, 9:47 a.m. UTC | #2 
Hi Simon

Thanks for your review!

On Thu, 30 Mar 2023 at 09:49, Simon Horman <horms@kernel.org> wrote:
>
> On Mon, Mar 27, 2023 at 05:06:53PM +0200, Ricardo Ribalda wrote:
> > Clang16 links the purgatory text in two sections:
> >
> >   [ 1] .text             PROGBITS         0000000000000000  00000040
> >        00000000000011a1  0000000000000000  AX       0     0     16
> >   [ 2] .rela.text        RELA             0000000000000000  00003498
> >        0000000000000648  0000000000000018   I      24     1     8
> >   ...
> >   [17] .text.hot.        PROGBITS         0000000000000000  00003220
> >        000000000000020b  0000000000000000  AX       0     0     1
> >   [18] .rela.text.hot.   RELA             0000000000000000  00004428
> >        0000000000000078  0000000000000018   I      24    17     8
> >
> > And both of them have their range [sh_addr ... sh_addr+sh_size] on the
> > area pointed by `e_entry`.
> >
> > This causes that image->start is calculated twice, once for .text and
> > another time for .text.hot. The second calculation leaves image->start
> > in a random location.
> >
> > Because of this, the system crashes inmediatly after:
>
> s/inmediatly/immediately/
>
> >
> > kexec_core: Starting new kernel
> >
> > Cc: stable@vger.kernel.org
>
> Maybe a fixes tag is warranted here.
>
> > Reviewed-by: Ross Zwisler <zwisler@google.com>
> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > ---
> >  kernel/kexec_file.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > index f1a0e4e3fb5c..25a37d8f113a 100644
> > --- a/kernel/kexec_file.c
> > +++ b/kernel/kexec_file.c
> > @@ -901,10 +901,21 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
> >               }
> >
> >               offset = ALIGN(offset, align);
> > +
> > +             /*
> > +              * Check if the segment contains the entry point, if so,
> > +              * calculate the value of image->start based on it.
> > +              * If the compiler has produced more than one .text sections
>
> nit: s/sections/section/
>
> > +              * (Eg: .text.hot), they are generally after the main .text
>
> If this is the general case, then are there cases where this doesn't hold?

When looking at this issue, I have only seen .text.hot after .text.
But I cannot warantee that future versions of llvm or gcc decide to
swap the order.

I am going to add a WARN whenever there are two overlapping .text
sections so the user has the chance to update their linker script.

>
> > +              * section, and they shall not be used to calculate
> > +              * image->start. So do not re-calculate image->start if it
> > +              * is not set to the initial value.
> > +              */
> >               if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
> >                   pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
> >                   pi->ehdr->e_entry < (sechdrs[i].sh_addr
> > -                                      + sechdrs[i].sh_size)) {
> > +                                      + sechdrs[i].sh_size) &&
> > +                 kbuf->image->start == pi->ehdr->e_entry) {
> >                       kbuf->image->start -= sechdrs[i].sh_addr;
> >                       kbuf->image->start += kbuf->mem + offset;
> >               }
> >
> > --
> > 2.40.0.348.gf938b09366-goog-b4-0.11.0-dev-696ae
> >
> > _______________________________________________
> > kexec mailing list
> > kexec@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> >



--
Ricardo Ribalda
diff mbox series

Patch

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index f1a0e4e3fb5c..25a37d8f113a 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -901,10 +901,21 @@  static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi,
 		}
 
 		offset = ALIGN(offset, align);
+
+		/*
+		 * Check if the segment contains the entry point, if so,
+		 * calculate the value of image->start based on it.
+		 * If the compiler has produced more than one .text sections
+		 * (Eg: .text.hot), they are generally after the main .text
+		 * section, and they shall not be used to calculate
+		 * image->start. So do not re-calculate image->start if it
+		 * is not set to the initial value.
+		 */
 		if (sechdrs[i].sh_flags & SHF_EXECINSTR &&
 		    pi->ehdr->e_entry >= sechdrs[i].sh_addr &&
 		    pi->ehdr->e_entry < (sechdrs[i].sh_addr
-					 + sechdrs[i].sh_size)) {
+					 + sechdrs[i].sh_size) &&
+		    kbuf->image->start == pi->ehdr->e_entry) {
 			kbuf->image->start -= sechdrs[i].sh_addr;
 			kbuf->image->start += kbuf->mem + offset;
 		}