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: Herbert Xu <herb...@gondor.apana.org.au>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Aditya Srivastava <yashsri...@gmail.com>
Cc: Randy Dunlap <rdun...@infradead.org>
Cc: linux-crypto@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
crypto/adiantum.c | 2 +-
drivers/crypto/amcc/crypto4xx_alg.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/crypto/adiantum.c b/crypto/adiantum.c
index 60f3883b736a..c2f62ca455af 100644
--- a/crypto/adiantum.c
+++ b/crypto/adiantum.c
@@ -190,7 +190,7 @@ static inline void le128_add(le128 *r, const le128 *v1,
const le128 *v2)
r->b = cpu_to_le64(x + y);
r->a = cpu_to_le64(le64_to_cpu(v1->a) + le64_to_cpu(v2->a) +
- (x + y < x));
+ (add_would_overflow(x, y)));
}
/* Subtraction in Z/(2^{128}Z) */
diff --git a/drivers/crypto/amcc/crypto4xx_alg.c
b/drivers/crypto/amcc/crypto4xx_alg.c
index e0af611a95d8..33f73234ddd9 100644
--- a/drivers/crypto/amcc/crypto4xx_alg.c
+++ b/drivers/crypto/amcc/crypto4xx_alg.c
@@ -251,7 +251,7 @@ crypto4xx_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)) {
SYNC_SKCIPHER_REQUEST_ON_STACK(subreq, ctx->sw_cipher.cipher);
int ret;
--
2.34.1
