linux-hardening - Re: [PATCH][next] drm/i915/uapi: Replace fake flex-array with flexible-array member

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Date:   Thu, 30 Mar 2023 14:13:41 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/i915/uapi: Replace fake flex-array with
 flexible-array member

Hi all,

Friendly ping: who can take this, please? 😄

Thanks
-- 
Gustavo

On 3/17/23 12:18, Gustavo A. R. Silva wrote:
> Zero-length arrays as fake flexible arrays are deprecated and we are
> moving towards adopting C99 flexible-array members instead.
> 
> Address the following warning found with GCC-13 and
> -fstrict-flex-arrays=3 enabled:
> drivers/gpu/drm/i915/gem/i915_gem_context.c: In function ‘set_proto_ctx_engines.isra’:
> drivers/gpu/drm/i915/gem/i915_gem_context.c:769:41: warning: array subscript n is outside array bounds of ‘struct i915_engine_class_instance[0]’ [-Warray-bounds=]
>    769 |                 if (copy_from_user(&ci, &user->engines[n], sizeof(ci))) {
>        |                                         ^~~~~~~~~~~~~~~~~
> ./include/uapi/drm/i915_drm.h:2494:43: note: while referencing ‘engines’
>   2494 |         struct i915_engine_class_instance engines[0];
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [1].
> 
> Link: https://github.com/KSPP/linux/issues/21
> Link: https://github.com/KSPP/linux/issues/271
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>   include/uapi/drm/i915_drm.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 8df261c5ab9b..5e458d6f2895 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -2491,7 +2491,7 @@ struct i915_context_param_engines {
>   #define I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE 0 /* see i915_context_engines_load_balance */
>   #define I915_CONTEXT_ENGINES_EXT_BOND 1 /* see i915_context_engines_bond */
>   #define I915_CONTEXT_ENGINES_EXT_PARALLEL_SUBMIT 2 /* see i915_context_engines_parallel_submit */
> -	struct i915_engine_class_instance engines[0];
> +	struct i915_engine_class_instance engines[];
>   } __attribute__((packed));
>   
>   #define I915_DEFINE_CONTEXT_PARAM_ENGINES(name__, N__) struct { \