linux-hardening - Re: [PATCH] drm/radeon: Remove __counted

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Message-ID: <CADnq5_P5Mz=Acm0HURUUHu03eBmemcu7jYe8nYJ5WtBjb93Qgg@mail.gmail.com>
Date: Thu, 30 May 2024 10:57:58 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Alex Deucher <alexander.deucher@....com>, 
	Christian König <christian.koenig@....com>, 
	Kees Cook <keescook@...omium.org>, "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, amd-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-hardening@...r.kernel.org, 
	llvm@...ts.linux.dev, patches@...ts.linux.dev, stable@...r.kernel.org
Subject: Re: [PATCH] drm/radeon: Remove __counted_by from StateArray.states[]

Applied.  Thanks!

On Wed, May 29, 2024 at 5:54 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> From: Bill Wendling <morbo@...gle.com>
>
> Work for __counted_by on generic pointers in structures (not just
> flexible array members) has started landing in Clang 19 (current tip of
> tree). During the development of this feature, a restriction was added
> to __counted_by to prevent the flexible array member's element type from
> including a flexible array member itself such as:
>
>   struct foo {
>     int count;
>     char buf[];
>   };
>
>   struct bar {
>     int count;
>     struct foo data[] __counted_by(count);
>   };
>
> because the size of data cannot be calculated with the standard array
> size formula:
>
>   sizeof(struct foo) * count
>
> This restriction was downgraded to a warning but due to CONFIG_WERROR,
> it can still break the build. The application of __counted_by on the
> states member of 'struct _StateArray' triggers this restriction,
> resulting in:
>
>   drivers/gpu/drm/radeon/pptable.h:442:5: error: 'counted_by' should not be applied to an array with element of unknown size because 'ATOM_PPLIB_STATE_V2' (aka 'struct _ATOM_PPLIB_STATE_V2') is a struct type with a flexible array member. This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size]
>     442 |     ATOM_PPLIB_STATE_V2 states[] __counted_by(ucNumEntries);
>         |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   1 error generated.
>
> Remove this use of __counted_by to fix the warning/error. However,
> rather than remove it altogether, leave it commented, as it may be
> possible to support this in future compiler releases.
>
> Cc: stable@...r.kernel.org
> Closes: https://github.com/ClangBuiltLinux/linux/issues/2028
> Fixes: efade6fe50e7 ("drm/radeon: silence UBSAN warning (v3)")
> Signed-off-by: Bill Wendling <morbo@...gle.com>
> Co-developed-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  drivers/gpu/drm/radeon/pptable.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/radeon/pptable.h b/drivers/gpu/drm/radeon/pptable.h
> index b7f22597ee95..969a8fb0ee9e 100644
> --- a/drivers/gpu/drm/radeon/pptable.h
> +++ b/drivers/gpu/drm/radeon/pptable.h
> @@ -439,7 +439,7 @@ typedef struct _StateArray{
>      //how many states we have
>      UCHAR ucNumEntries;
>
> -    ATOM_PPLIB_STATE_V2 states[] __counted_by(ucNumEntries);
> +    ATOM_PPLIB_STATE_V2 states[] /* __counted_by(ucNumEntries) */;
>  }StateArray;
>
>
>
> ---
> base-commit: e64e8f7c178e5228e0b2dbb504b9dc75953a319f
> change-id: 20240529-drop-counted-by-radeon-states-state-array-01936ded4c18
>
> Best regards,
> --
> Nathan Chancellor <nathan@...nel.org>
>