In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:
VAR + value < VAR
Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.
Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.
Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Jesper Nilsson <jesper.nils...@axis.com>
Cc: Lars Persson <lars.pers...@axis.com>
Cc: Herbert Xu <herb...@gondor.apana.org.au>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: linux-arm-ker...@axis.com
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
drivers/crypto/axis/artpec6_crypto.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/crypto/axis/artpec6_crypto.c
b/drivers/crypto/axis/artpec6_crypto.c
index dbc1d483f2af..cbec539f0e20 100644
--- a/drivers/crypto/axis/artpec6_crypto.c
+++ b/drivers/crypto/axis/artpec6_crypto.c
@@ -1190,7 +1190,7 @@ artpec6_crypto_ctr_crypt(struct skcipher_request *req,
bool encrypt)
* the whole IV is a counter. So fallback if the counter is going to
* overlow.
*/
- if (counter + nblks < counter) {
+ if (add_would_overflow(counter, nblks)) {
int ret;
pr_debug("counter %x will overflow (nblks %u), falling back\n",
--
2.34.1
