crypto: verify_pefile - Use constant-time digest comparison

The PE file digest comparison in verify_pefile_signature() uses memcmp(), whose execution time depends on the position of the first mismatched byte. This creates a timing side-channel that could allow an attacker to forge PE file signatures byte by byte.

Replace memcmp() with crypto_memneq() to perform a constant-time comparison, consistent with the rest of the crypto subsystem (gcm, ccm, chacha20poly1305, rsassa-pkcs1, krb5, etc.). Add an explicit <crypto/utils.h> include since this file did not previously pull in the crypto_memneq() declaration.

---
 crypto/asymmetric_keys/verify_pefile.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index cec99db14129..dce40a2a3fac 100644
@@ -14,6 +14,7 @@
 #include <linux/asn1.h>
 #include <linux/verification.h>
 #include <crypto/hash.h>
+#include <crypto/utils.h>
 #include "verify_pefile.h"
 
 /*

@@ -374,7 +375,7 @@ static int pefile_digest_pe(const void *pebuf, unsigned int pelen,
 	/* Check that the PE file digest matches that in the MSCODE part of the
 	 * PKCS#7 certificate.
 	 */
-	if (memcmp(digest, ctx->digest, ctx->digest_len) != 0) {
+	if (crypto_memneq(digest, ctx->digest, ctx->digest_len)) {
 		pr_warn("Digest mismatch\n");
 		ret = -EKEYREJECTED;
 	} else {

2.25.1