Re: [RFC][PATCH] x86/mm: Disconnect RWX module checking from execmem

[Frédéric MARIE-JOSEPH]

On 10/1/26 13:19, Dave Hansen wrote:
> Link: https://lore.kernel.org/all/20261001-x86-fault-spurious-rw-v1-1-7fe1189b5efd@xxxxxxxxxxx/

Thanks for turning this into a patch. Not sure about the link.
It points to Hitesh Murali's spurious_kernel_fault_check() patch;
In case of typo this one is my report:
https://lore.kernel.org/lkml/CAHD2OOfP=h=qS6nP4dtn7RTQqMEqOvXD+iURXJ7Rgc5KFjgi5A@xxxxxxxxxxxxxx/

Regards,
Frederic


Le jeu. 1 oct. 2026 à 22:19, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> a écrit :
>
>
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> Frédéric reported:
>
>         x86/mm: Checked W+X mappings: FAILED, 7 W+X pages found.
>
> errors on a build with modules disabled. There are some build
> dependencies in play:
>
>  * ARCH_HAS_EXECMEM_ROX depends on STRICT_MODULE_RWX
>  * STRICT_MODULE_RWX depends on MODULES
>  * execmem_restore_rox() is a stub without ARCH_HAS_EXECMEM_ROX=y
>
> execmem_restore_rox() is what the x86 "ITS" code uses to zap its
> W+X mappings during early boot. The error message comes from
> CONFIG_DEBUG_WX which is independent from any of the other options.
>
> But the nutty part is that there is any connection at all between
> ARCH_HAS_EXECMEM_ROX and STRICT_MODULE_RWX.
>
> Restore a functional execmem_restore_rox() to all 64-bit builds by
> eliminating the STRICT_MODULE_RWX dependency.
>
> Then, turn our attention to execmem. 47410d839fcd "x86/Kconfig: only
> enable ROX cache...") was trying to make module memory access more
> permissive unless STRICT_MODULE_RWX is in play. For execmem, never
> consider module memory to be ROX except under STRICT_MODULE_RWX.
>
> This seems to fix Frédéric's issue, but I'm a bit worried that it
> has other implications in the execmem code. For instance, the
> module_enable_text_rox() loop is now rather weird mem->is_rox is
> now directly dependent on STRICT_MODULE_RWX.
>
> Mike, do you see anything bad happening on the execmem side if we
> do this?
>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Tested-by: Frederic MARIE-JOSEPH <fredericmariejoseph@xxxxxxxxx>
> Reported-by: Frederic MARIE-JOSEPH <fredericmariejoseph@xxxxxxxxx>
> Link: https://lore.kernel.org/all/20261001-x86-fault-spurious-rw-v1-1-7fe1189b5efd@xxxxxxxxxxx/
> Fixes: a82b26451de1 ("x86/its: explicitly manage permissions for ITS pages")
> Cc: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> Cc: Petr Pavlu <petr.pavlu@xxxxxxxx>
> Cc: Daniel Gomez <da.gomez@xxxxxxxxxx>
> Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> Cc: Aaron Tomlin <atomlin@xxxxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-modules@xxxxxxxxxxxxxxx
> ---
>
>  b/arch/x86/Kconfig     |    2 +-
>  b/kernel/module/main.c |    3 ++-
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff -puN arch/x86/Kconfig~x86-STRICT_MODULE_RWX arch/x86/Kconfig
> --- a/arch/x86/Kconfig~x86-STRICT_MODULE_RWX    2026-10-01 07:11:50.443595828 -0700
> +++ b/arch/x86/Kconfig  2026-10-01 07:11:50.454595751 -0700
> @@ -85,7 +85,7 @@ config X86
>         select ARCH_HAS_DMA_OPS                 if GART_IOMMU || XEN
>         select ARCH_HAS_EARLY_DEBUG             if KGDB
>         select ARCH_HAS_ELF_RANDOMIZE
> -       select ARCH_HAS_EXECMEM_ROX             if X86_64 && STRICT_MODULE_RWX
> +       select ARCH_HAS_EXECMEM_ROX             if X86_64
>         select ARCH_HAS_FAST_MULTIPLIER
>         select ARCH_HAS_FORTIFY_SOURCE
>         select ARCH_HAS_GCOV_PROFILE_ALL
> diff -puN kernel/module/main.c~x86-STRICT_MODULE_RWX kernel/module/main.c
> --- a/kernel/module/main.c~x86-STRICT_MODULE_RWX        2026-10-01 07:11:50.449595786 -0700
> +++ b/kernel/module/main.c      2026-10-01 09:47:20.842360625 -0700
> @@ -1355,7 +1355,8 @@ static int module_memory_alloc(struct mo
>         if (!ptr)
>                 return -ENOMEM;
>
> -       mod->mem[type].is_rox = execmem_is_rox(execmem_type);
> +       if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
> +               mod->mem[type].is_rox = execmem_is_rox(execmem_type);
>
>         /*
>          * The pointer to these blocks of memory are stored on the module
> _