linux-kernel - Re: [PATCH][next] drm/amdgpu/discovery: Replace fake flex-arrays with flexible-array members

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Date:   Tue, 30 May 2023 16:08:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] drm/amdgpu/discovery: Replace fake flex-arrays
 with flexible-array members

On Sun, May 28, 2023 at 02:26:37PM -0600, Gustavo A. R. Silva wrote:
> Zero-length and one-element arrays are deprecated, and we are moving
> towards adopting C99 flexible-array members, instead.
> 
> Use the DECLARE_FLEX_ARRAY() helper macro to transform zero-length
> arrays in a union into flexible-array members. And replace a one-element
> array with a C99 flexible-array member.
> 
> Address the following warnings found with GCC-13 and
> -fstrict-flex-arrays=3 enabled:
> drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1009:89: warning: array subscript kk is outside array bounds of ‘uint32_t[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
> drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1007:94: warning: array subscript kk is outside array bounds of ‘uint64_t[0]’ {aka ‘long long unsigned int[]’} [-Warray-bounds=]
> drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1310:94: warning: array subscript k is outside array bounds of ‘uint64_t[0]’ {aka ‘long long unsigned int[]’} [-Warray-bounds=]
> drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c:1309:57: warning: array subscript k is outside array bounds of ‘uint32_t[0]’ {aka ‘unsigned int[]’} [-Warray-bounds=]
> 
> 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].
> 
> This results in no differences in binary output.
> 
> Link: https://github.com/KSPP/linux/issues/21
> Link: https://github.com/KSPP/linux/issues/193
> Link: https://github.com/KSPP/linux/issues/300
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook