linux-hardening - [PATCH] nouveau/gsp: Avoid addressing beyond end of rpc->entries

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Message-Id: <20240330141159.work.063-kees@kernel.org>
Date: Sat, 30 Mar 2024 07:12:03 -0700
From: Kees Cook <keescook@...omium.org>
To: Karol Herbst <kherbst@...hat.com>
Cc: Kees Cook <keescook@...omium.org>,
	Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...hat.com>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>,
	Dave Airlie <airlied@...hat.com>,
	Ben Skeggs <bskeggs@...hat.com>,
	Timur Tabi <ttabi@...dia.com>,
	dri-devel@...ts.freedesktop.org,
	nouveau@...ts.freedesktop.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Dan Carpenter <dan.carpenter@...aro.org>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] nouveau/gsp: Avoid addressing beyond end of rpc->entries

Using the end of rpc->entries[] for addressing runs into both compile-time
and run-time detection of accessing beyond the end of the array. Use the
base pointer instead, since was allocated with the additional bytes for
storing the strings. Avoids the following warning in future GCC releases
with support for __counted_by:

In function 'fortify_memcpy_chk',
    inlined from 'r535_gsp_rpc_set_registry' at ../drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c:1123:3:
../include/linux/fortify-string.h:553:25: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
  553 |                         __write_overflow_field(p_size_field, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

for this code:

	strings = (char *)&rpc->entries[NV_GSP_REG_NUM_ENTRIES];
	...
                memcpy(strings, r535_registry_entries[i].name, name_len);

Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: Karol Herbst <kherbst@...hat.com>
Cc: Lyude Paul <lyude@...hat.com>
Cc: Danilo Krummrich <dakr@...hat.com>
Cc: David Airlie <airlied@...il.com>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: Dave Airlie <airlied@...hat.com>
Cc: Ben Skeggs <bskeggs@...hat.com>
Cc: Timur Tabi <ttabi@...dia.com>
Cc: dri-devel@...ts.freedesktop.org
Cc: nouveau@...ts.freedesktop.org
---
 drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
index 9994cbd6f1c4..9858c1438aa7 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
@@ -1112,7 +1112,7 @@ r535_gsp_rpc_set_registry(struct nvkm_gsp *gsp)
 	rpc->numEntries = NV_GSP_REG_NUM_ENTRIES;
 
 	str_offset = offsetof(typeof(*rpc), entries[NV_GSP_REG_NUM_ENTRIES]);
-	strings = (char *)&rpc->entries[NV_GSP_REG_NUM_ENTRIES];
+	strings = (char *)rpc + str_offset;
 	for (i = 0; i < NV_GSP_REG_NUM_ENTRIES; i++) {
 		int name_len = strlen(r535_registry_entries[i].name) + 1;
 
-- 
2.34.1