linux-kernel - Re: [PATCH][next] nouveau/gsp: replace zero-length array with flex-array member and use __counted

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Message-ID: <202311161028.E780FBB146@keescook>
Date:   Thu, 16 Nov 2023 10:28:37 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
        Danilo Krummrich <dakr@...hat.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] nouveau/gsp: replace zero-length array with
 flex-array member and use __counted_by

On Thu, Nov 16, 2023 at 12:11:43PM -0600, Gustavo A. R. Silva wrote:
> Fake flexible arrays (zero-length and one-element arrays) are deprecated,
> and should be replaced by flexible-array members. So, replace
> zero-length array with a flexible-array member in `struct
> PACKED_REGISTRY_TABLE`.
> 
> Also annotate array `entries` with `__counted_by()` to prepare for the
> coming implementation by GCC and Clang of the `__counted_by` attribute.
> Flexible array members annotated with `__counted_by` can have their
> accesses bounds-checked at run-time via `CONFIG_UBSAN_BOUNDS` (for array
> indexing) and `CONFIG_FORTIFY_SOURCE` (for strcpy/memcpy-family functions).
> 
> This fixes multiple -Warray-bounds warnings:
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c:1069:29: warning: array subscript 0 is outside array bounds of 'PACKED_REGISTRY_ENTRY[0]' [-Warray-bounds=]
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c:1070:29: warning: array subscript 0 is outside array bounds of 'PACKED_REGISTRY_ENTRY[0]' [-Warray-bounds=]
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c:1071:29: warning: array subscript 0 is outside array bounds of 'PACKED_REGISTRY_ENTRY[0]' [-Warray-bounds=]
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c:1072:29: warning: array subscript 0 is outside array bounds of 'PACKED_REGISTRY_ENTRY[0]' [-Warray-bounds=]
> 
> While there, also make use of the struct_size() helper, and address
> checkpatch.pl warning:
> WARNING: please, no spaces at the start of a line
> 
> This results in no differences in binary output.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks nice to me.

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

-- 
Kees Cook