[PATCH] [v2] crypto: drivers - avoid memcpy size warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

Some configurations with gcc-12 or gcc-13 produce a warning for the source
and destination of a memcpy() in atmel_sha_hmac_compute_ipad_hash() potentially
overlapping:

In file included from include/linux/string.h:254,
                 from drivers/crypto/atmel-sha.c:15:
drivers/crypto/atmel-sha.c: In function 'atmel_sha_hmac_compute_ipad_hash':
include/linux/fortify-string.h:57:33: error: '__builtin_memcpy' accessing 129 or more bytes at offsets 408 and 280 overlaps 1 or more bytes at offset 408 [-Werror=restrict]
   57 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^
include/linux/fortify-string.h:648:9: note: in expansion of macro '__underlying_memcpy'
  648 |         __underlying_##op(p, q, __fortify_size);                        \
      |         ^~~~~~~~~~~~~
include/linux/fortify-string.h:693:26: note: in expansion of macro '__fortify_memcpy_chk'
  693 | #define memcpy(p, q, s)  __fortify_memcpy_chk(p, q, s,                  \
      |                          ^~~~~~~~~~~~~~~~~~~~
drivers/crypto/atmel-sha.c:1773:9: note: in expansion of macro 'memcpy'
 1773 |         memcpy(hmac->opad, hmac->ipad, bs);
      |         ^~~~~~

The same thing happens in two more drivers that have the same logic:

drivers/crypto/chelsio/chcr_algo.c: In function 'chcr_ahash_setkey':
include/linux/fortify-string.h:57:33: error: '__builtin_memcpy' accessing 129 or more bytes at offsets 260 and 132 overlaps 1 or more bytes at offset 260 [-Werror=restrict]
drivers/crypto/bcm/cipher.c: In function 'ahash_hmac_setkey':
include/linux/fortify-string.h:57:33: error: '__builtin_memcpy' accessing between 129 and 4294967295 bytes at offsets 840 and 712 overlaps between 1 and 4294967167 bytes at offset 840 [-Werror=restrict]

I don't think it can actually happen because the size is strictly bounded
to the available block sizes, at most 128 bytes, though inlining decisions
could lead gcc to not see that.

Use the unsafe_memcpy() helper instead of memcpy(), with the only difference
being that this skips the hardening checks that produce the warning.

Suggested-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/crypto/atmel-sha.c         | 3 ++-
 drivers/crypto/bcm/cipher.c        | 3 ++-
 drivers/crypto/chelsio/chcr_algo.c | 3 ++-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/crypto/atmel-sha.c b/drivers/crypto/atmel-sha.c
index 54fec72dfba27..99a9ff8e743f2 100644
--- a/drivers/crypto/atmel-sha.c
+++ b/drivers/crypto/atmel-sha.c
@@ -1770,7 +1770,8 @@ static int atmel_sha_hmac_compute_ipad_hash(struct atmel_sha_dev *dd)
 	size_t bs = ctx->block_size;
 	size_t i, num_words = bs / sizeof(u32);
 
-	memcpy(hmac->opad, hmac->ipad, bs);
+	unsafe_memcpy(hmac->opad, hmac->ipad, bs,
+		      "fortified memcpy causes -Wrestrict warning");
 	for (i = 0; i < num_words; ++i) {
 		hmac->ipad[i] ^= 0x36363636;
 		hmac->opad[i] ^= 0x5c5c5c5c;
diff --git a/drivers/crypto/bcm/cipher.c b/drivers/crypto/bcm/cipher.c
index 70b911baab26d..4c46357e2570e 100644
--- a/drivers/crypto/bcm/cipher.c
+++ b/drivers/crypto/bcm/cipher.c
@@ -2397,7 +2397,8 @@ static int ahash_hmac_setkey(struct crypto_ahash *ahash, const u8 *key,
 		memset(ctx->ipad + ctx->authkeylen, 0,
 		       blocksize - ctx->authkeylen);
 		ctx->authkeylen = 0;
-		memcpy(ctx->opad, ctx->ipad, blocksize);
+		unsafe_memcpy(ctx->opad, ctx->ipad, blocksize,
+			      "fortified memcpy causes -Wrestrict warning");
 
 		for (index = 0; index < blocksize; index++) {
 			ctx->ipad[index] ^= HMAC_IPAD_VALUE;
diff --git a/drivers/crypto/chelsio/chcr_algo.c b/drivers/crypto/chelsio/chcr_algo.c
index 0eade4fa6695b..16298ae4a00bf 100644
--- a/drivers/crypto/chelsio/chcr_algo.c
+++ b/drivers/crypto/chelsio/chcr_algo.c
@@ -2216,7 +2216,8 @@ static int chcr_ahash_setkey(struct crypto_ahash *tfm, const u8 *key,
 		memcpy(hmacctx->ipad, key, keylen);
 	}
 	memset(hmacctx->ipad + keylen, 0, bs - keylen);
-	memcpy(hmacctx->opad, hmacctx->ipad, bs);
+	unsafe_memcpy(hmacctx->opad, hmacctx->ipad, bs,
+		      "fortified memcpy causes -Wrestrict warning");
 
 	for (i = 0; i < bs / sizeof(int); i++) {
 		*((unsigned int *)(&hmacctx->ipad) + i) ^= IPAD_DATA;
-- 
2.39.2