[PATCH] crypto/caam: Avoid GCC constprop bug warning

Kees Cook
2022-10-28T21:05:47Z

GCC 12 appears to perform constant propagation incompletely(?) and can
no longer notice that "len" is always 0 when "data" is NULL. Expand the
check to avoid warnings about memcpy() having a NULL argument:

...
from drivers/crypto/caam/key_gen.c:8:
drivers/crypto/caam/desc_constr.h: In function 'append_data.constprop':
include/linux/fortify-string.h:48:33: warning: argument 2 null where non-null expected [-Wnonnull]
48 | #define __underlying_memcpy __builtin_memcpy
| ^
include/linux/fortify-string.h:438:9: note: in expansion of macro '__underlying_memcpy'
438 | __underlying_##op(p, q, __fortify_size); \
| ^~~~~~~~~~~~~

The NULL was being propagated from:

append_fifo_load_as_imm(desc, NULL, 0, LDST_CLASS_2_CCB |
FIFOLD_TYPE_MSG | FIFOLD_TYPE_LAST2);
...
static inline void append_##cmd##_as_imm(u32 * const desc, const void *data, \
unsigned int len, u32 options) \
{ \
PRINT_POS; \
append_cmd_data(desc, data, len, CMD_##op | options); \
}
...
APPEND_CMD_PTR_TO_IMM(fifo_load, FIFO_LOAD);
...
static inline void append_cmd_data(u32 * const desc, const void *data, int len,
u32 command)
{
append_cmd(desc, command | IMMEDIATE | len);
append_data(desc, data, len);
}

Cc: "Horia Geantă" <horia.geanta@nxp.com>
Cc: Pankaj Gupta <pankaj.gupta@nxp.com>
Cc: Gaurav Jain <gaurav.jain@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-crypto@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/202210290446.qBayTfzl-lkp@intel.com
Signed-off-by: Kees Cook <keescook@chromium.org>
---
drivers/crypto/caam/desc_constr.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/crypto/caam/desc_constr.h b/drivers/crypto/caam/desc_constr.h
index 62ce6421bb3f..ddbba8b00ab7 100644
--- a/drivers/crypto/caam/desc_constr.h
+++ b/drivers/crypto/caam/desc_constr.h
@@ -163,7 +163,7 @@ static inline void append_data(u32 * const desc, const void *data, int len)
{
u32 *offset = desc_end(desc);

- if (len) /* avoid sparse warning: memcpy with byte count of 0 */
+ if (data && len) /* avoid sparse warning: memcpy with byte count of 0 */
memcpy(offset, data, len);

(*desc) = cpu_to_caam32(caam32_to_cpu(*desc) +
--
2.34.1