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

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Message-ID: <ZVZxXiXYIzEwUE3N@pollux>
Date: Thu, 16 Nov 2023 20:45:34 +0100
From: Danilo Krummrich <dakr@...hat.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	nouveau@...ts.freedesktop.org, linux-hardening@...r.kernel.org,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH][next] nouveau/gsp: replace zero-length array with
 flex-array member and use __counted_by

Hi Gustavo,

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>
> ---
>  .../nvrm/535.113.01/nvidia/generated/g_os_nvoc.h   | 14 +++++++-------
>  drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c     |  2 +-
>  2 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/include/nvrm/535.113.01/nvidia/generated/g_os_nvoc.h b/drivers/gpu/drm/nouveau/include/nvrm/535.113.01/nvidia/generated/g_os_nvoc.h
> index 754c6af42f30..259b25c2ac6b 100644
> --- a/drivers/gpu/drm/nouveau/include/nvrm/535.113.01/nvidia/generated/g_os_nvoc.h
> +++ b/drivers/gpu/drm/nouveau/include/nvrm/535.113.01/nvidia/generated/g_os_nvoc.h
> @@ -28,17 +28,17 @@
>  
>  typedef struct PACKED_REGISTRY_ENTRY
>  {
> -    NvU32                   nameOffset;
> -    NvU8                    type;
> -    NvU32                   data;
> -    NvU32                   length;
> +	NvU32                   nameOffset;
> +	NvU8                    type;
> +	NvU32                   data;
> +	NvU32                   length;
>  } PACKED_REGISTRY_ENTRY;
>  
>  typedef struct PACKED_REGISTRY_TABLE
>  {
> -    NvU32                   size;
> -    NvU32                   numEntries;
> -    PACKED_REGISTRY_ENTRY   entries[0];
> +	NvU32                   size;
> +	NvU32                   numEntries;
> +	PACKED_REGISTRY_ENTRY   entries[] __counted_by(numEntries);
>  } PACKED_REGISTRY_TABLE;

Thanks for the fix!

However, I have some concerns about changing those header files, since they're
just copied over from Nvidia's driver [1].

Once we add the header files for a new firmware revision, we'd potentially run
into the same issue, applying the same fix again.

As I already mentioned for Timur's patch [2], I'd prefer to get a fix upstream
(meaning [1] in this case). Of course, that's probably more up to Timur to tell
if this will work out.

If we can't get a fix upstream, I'd probably prefer to silence warning
elsewhere.

[1] https://github.com/NVIDIA/open-gpu-kernel-modules
[2] https://lore.kernel.org/all/20231107234726.854248-1-ttabi@nvidia.com/T/

>  
>  #endif
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
> index dc44f5c7833f..228335487af5 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
> @@ -1048,7 +1048,7 @@ r535_gsp_rpc_set_registry(struct nvkm_gsp *gsp)
>  	char *strings;
>  	int str_offset;
>  	int i;
> -	size_t rpc_size = sizeof(*rpc) + sizeof(rpc->entries[0]) * NV_GSP_REG_NUM_ENTRIES;
> +	size_t rpc_size = struct_size(rpc, entries, NV_GSP_REG_NUM_ENTRIES);
>  
>  	/* add strings + null terminator */
>  	for (i = 0; i < NV_GSP_REG_NUM_ENTRIES; i++)
> -- 
> 2.34.1
>