[v8,0/1] riscv: Allow to downgrade paging mode from the command line

  This new version gets rid of the limitation that prevented KASAN kernels         
to use the newly introduced parameters.                                          
                                                                                 
While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:         
avoid relocating the kernel twice for KASLR"): it allows to use the fdt          
functions very early in the boot process with KASAN enabled by simply            
compiling a new version of those functions without instrumentation.              
                                                                                 
I had to change the handling of the command line parsing to make the             
code self-contained in kernel/pi/cmd_early.c to avoid calling too many           
__pi prefixed functions from outside this file.                                  
                                                                                 
I'll use this approach like arm64 to handle the extraction of the random         
seedi from the device tree for KASLR. 

base-commit: eb9be8310c58 ("RISC-V: add a spin_shadow_stack declaration")

v8:
- Fix LLVM ld warning by moving the section .init.sdata from
  kernel/pi/string.c into the newly created section .init.pidata

v7:
- Rebased on top of for-next which introduces lots of errors (thanks to
  the patchwork CI)
- Add __NO_FORTIFY to avoid undefined __pi_fortify_panic
- Add an alias to our newly introduced strlen
- Remove __init as sections are already prefixed in the Makefile
- Introduce new section for kernel/pi/string.c to quiet the following
  warnings (once we have all the string functions, we'll be able to get
  rid of this):

warning: orphan section `.init__bug_table' from `arch/riscv/kernel/pi/string.pi.o' being placed in section `.init__bug_table'
warning: orphan section `.init.srodata.cst8' from `arch/riscv/kernel/pi/string.pi.o' being placed in section `.init.srodata.cst8'

v6:
- Fix llvm warning by forward declaring set_satp_mode_from_cmdline

v5:                                                                              
- Handle null command line, Thanks Björn!                                        
- Add RB/TB from Björn                                                           
                                                                                 
v4:                                                                              
- Introduce pi/ for KASAN to work                                                
                                                                                 
v3:                                                                              
- Massage commit log to make no4lvl clearer, as asked by Conor                   
- Add a note to kernel-parameters.txt regarding the impossibility to use         
  those parameters when KASAN is enabled, as suggested by Conor                  
- Add RB from Björn                                                              
                                                                                 
v2:                                                                              
- Honor CMDLINE_EXTEND and CMDLINE_FORCE as noticed by Björn


Alexandre Ghiti (1):
  riscv: Allow to downgrade paging mode from the command line

 .../admin-guide/kernel-parameters.txt         |  5 +-
 arch/riscv/kernel/Makefile                    |  2 +
 arch/riscv/kernel/pi/Makefile                 | 37 +++++++++++
 arch/riscv/kernel/pi/cmdline_early.c          | 62 +++++++++++++++++++
 arch/riscv/kernel/vmlinux.lds.S               |  8 +++
 arch/riscv/lib/memcpy.S                       |  2 +
 arch/riscv/lib/memmove.S                      |  2 +
 arch/riscv/lib/strlen.S                       |  1 +
 arch/riscv/mm/init.c                          | 36 +++++++++--
 9 files changed, 148 insertions(+), 7 deletions(-)
 create mode 100644 arch/riscv/kernel/pi/Makefile
 create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
  

On Tue, 28 Feb 2023 07:46:28 PST (-0800), alexghiti@rivosinc.com wrote:
> This new version gets rid of the limitation that prevented KASAN kernels
> to use the newly introduced parameters.
>
> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> functions very early in the boot process with KASAN enabled by simply
> compiling a new version of those functions without instrumentation.
>
> I had to change the handling of the command line parsing to make the
> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> __pi prefixed functions from outside this file.
>
> I'll use this approach like arm64 to handle the extraction of the random
> seedi from the device tree for KASLR.
>
> base-commit: eb9be8310c58 ("RISC-V: add a spin_shadow_stack declaration")

I have that in my tree, I'm still getting a bunch of boot failures 
though.  I can try to get a list if you're not seeing any, but I'm kind 
of stuck on some other stuff for a bit...

> v8:
> - Fix LLVM ld warning by moving the section .init.sdata from
>   kernel/pi/string.c into the newly created section .init.pidata
>
> v7:
> - Rebased on top of for-next which introduces lots of errors (thanks to
>   the patchwork CI)
> - Add __NO_FORTIFY to avoid undefined __pi_fortify_panic
> - Add an alias to our newly introduced strlen
> - Remove __init as sections are already prefixed in the Makefile
> - Introduce new section for kernel/pi/string.c to quiet the following
>   warnings (once we have all the string functions, we'll be able to get
>   rid of this):
>
> warning: orphan section `.init__bug_table' from `arch/riscv/kernel/pi/string.pi.o' being placed in section `.init__bug_table'
> warning: orphan section `.init.srodata.cst8' from `arch/riscv/kernel/pi/string.pi.o' being placed in section `.init.srodata.cst8'
>
> v6:
> - Fix llvm warning by forward declaring set_satp_mode_from_cmdline
>
> v5:
> - Handle null command line, Thanks Björn!
> - Add RB/TB from Björn
>
> v4:
> - Introduce pi/ for KASAN to work
>
> v3:
> - Massage commit log to make no4lvl clearer, as asked by Conor
> - Add a note to kernel-parameters.txt regarding the impossibility to use
>   those parameters when KASAN is enabled, as suggested by Conor
> - Add RB from Björn
>
> v2:
> - Honor CMDLINE_EXTEND and CMDLINE_FORCE as noticed by Björn
>
>
> Alexandre Ghiti (1):
>   riscv: Allow to downgrade paging mode from the command line
>
>  .../admin-guide/kernel-parameters.txt         |  5 +-
>  arch/riscv/kernel/Makefile                    |  2 +
>  arch/riscv/kernel/pi/Makefile                 | 37 +++++++++++
>  arch/riscv/kernel/pi/cmdline_early.c          | 62 +++++++++++++++++++
>  arch/riscv/kernel/vmlinux.lds.S               |  8 +++
>  arch/riscv/lib/memcpy.S                       |  2 +
>  arch/riscv/lib/memmove.S                      |  2 +
>  arch/riscv/lib/strlen.S                       |  1 +
>  arch/riscv/mm/init.c                          | 36 +++++++++--
>  9 files changed, 148 insertions(+), 7 deletions(-)
>  create mode 100644 arch/riscv/kernel/pi/Makefile
>  create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
  

On 3/29/23 19:59, Palmer Dabbelt wrote:
> On Tue, 28 Feb 2023 07:46:28 PST (-0800), alexghiti@rivosinc.com wrote:
>> This new version gets rid of the limitation that prevented KASAN kernels
>> to use the newly introduced parameters.
>>
>> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
>> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
>> functions very early in the boot process with KASAN enabled by simply
>> compiling a new version of those functions without instrumentation.
>>
>> I had to change the handling of the command line parsing to make the
>> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
>> __pi prefixed functions from outside this file.
>>
>> I'll use this approach like arm64 to handle the extraction of the random
>> seedi from the device tree for KASLR.
>>
>> base-commit: eb9be8310c58 ("RISC-V: add a spin_shadow_stack 
>> declaration")
>
> I have that in my tree, I'm still getting a bunch of boot failures 
> though.  I can try to get a list if you're not seeing any, but I'm 
> kind of stuck on some other stuff for a bit...


I sent yesterday a v9 which fixes the medlow boot issues you mentioned, 
I did not have any boot failures after that on my side.


>
>> v8:
>> - Fix LLVM ld warning by moving the section .init.sdata from
>>   kernel/pi/string.c into the newly created section .init.pidata
>>
>> v7:
>> - Rebased on top of for-next which introduces lots of errors (thanks to
>>   the patchwork CI)
>> - Add __NO_FORTIFY to avoid undefined __pi_fortify_panic
>> - Add an alias to our newly introduced strlen
>> - Remove __init as sections are already prefixed in the Makefile
>> - Introduce new section for kernel/pi/string.c to quiet the following
>>   warnings (once we have all the string functions, we'll be able to get
>>   rid of this):
>>
>> warning: orphan section `.init__bug_table' from 
>> `arch/riscv/kernel/pi/string.pi.o' being placed in section 
>> `.init__bug_table'
>> warning: orphan section `.init.srodata.cst8' from 
>> `arch/riscv/kernel/pi/string.pi.o' being placed in section 
>> `.init.srodata.cst8'
>>
>> v6:
>> - Fix llvm warning by forward declaring set_satp_mode_from_cmdline
>>
>> v5:
>> - Handle null command line, Thanks Björn!
>> - Add RB/TB from Björn
>>
>> v4:
>> - Introduce pi/ for KASAN to work
>>
>> v3:
>> - Massage commit log to make no4lvl clearer, as asked by Conor
>> - Add a note to kernel-parameters.txt regarding the impossibility to use
>>   those parameters when KASAN is enabled, as suggested by Conor
>> - Add RB from Björn
>>
>> v2:
>> - Honor CMDLINE_EXTEND and CMDLINE_FORCE as noticed by Björn
>>
>>
>> Alexandre Ghiti (1):
>>   riscv: Allow to downgrade paging mode from the command line
>>
>>  .../admin-guide/kernel-parameters.txt         |  5 +-
>>  arch/riscv/kernel/Makefile                    |  2 +
>>  arch/riscv/kernel/pi/Makefile                 | 37 +++++++++++
>>  arch/riscv/kernel/pi/cmdline_early.c          | 62 +++++++++++++++++++
>>  arch/riscv/kernel/vmlinux.lds.S               |  8 +++
>>  arch/riscv/lib/memcpy.S                       |  2 +
>>  arch/riscv/lib/memmove.S                      |  2 +
>>  arch/riscv/lib/strlen.S                       |  1 +
>>  arch/riscv/mm/init.c                          | 36 +++++++++--
>>  9 files changed, 148 insertions(+), 7 deletions(-)
>>  create mode 100644 arch/riscv/kernel/pi/Makefile
>>  create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
>
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