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

Anders Roxell
2022-12-02T00:58:25Z

On 2022-10-28 14:05, Kees Cook wrote:
> 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>

Tested-by: Anders Roxell <anders.roxell@linaro.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 */

Maybe we should update the comment, since newer releases of sparse
doesn't warn about this.

Cheers,
Anders