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@chromium.org>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240330141159.work.063-kees@kernel.org

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c b/drivers/gpu/drm/nouveau/nvkm/subdev/gsp/r535.c
index 9994cbd6f1c40c0c798498687f4f5d7168e883c5..9858c1438aa7feda7d84ff5442f611b23f101b2d 100644 (file)
--- 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;