linux-kernel - [PATCH 1/3] KEYS: trusted_tpm1: Compare HMAC values in constant time

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Message-ID: <20250731212354.105044-2-ebiggers@kernel.org>
Date: Thu, 31 Jul 2025 14:23:52 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: James Bottomley <James.Bottomley@...senPartnership.com>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Mimi Zohar <zohar@...ux.ibm.com>,
	keyrings@...r.kernel.org
Cc: David Howells <dhowells@...hat.com>,
	linux-integrity@...r.kernel.org,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Eric Biggers <ebiggers@...nel.org>,
	stable@...r.kernel.org
Subject: [PATCH 1/3] KEYS: trusted_tpm1: Compare HMAC values in constant time

To prevent timing attacks, HMAC value comparison needs to be constant
time.  Replace the memcmp() with the correct function, crypto_memneq().

Fixes: d00a1c72f7f4 ("keys: add new trusted key-type")
Cc: stable@...r.kernel.org
Signed-off-by: Eric Biggers <ebiggers@...nel.org>
---
 security/keys/trusted-keys/trusted_tpm1.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index 89c9798d18007..e73f2c6c817a0 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -5,10 +5,11 @@
  *
  * See Documentation/security/keys/trusted-encrypted.rst
  */
 
 #include <crypto/hash_info.h>
+#include <crypto/utils.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/parser.h>
 #include <linux/string.h>
 #include <linux/err.h>
@@ -239,11 +240,11 @@ int TSS_checkhmac1(unsigned char *buffer,
 			  TPM_NONCE_SIZE, enonce, TPM_NONCE_SIZE, ononce,
 			  1, continueflag, 0, 0);
 	if (ret < 0)
 		goto out;
 
-	if (memcmp(testhmac, authdata, SHA1_DIGEST_SIZE))
+	if (crypto_memneq(testhmac, authdata, SHA1_DIGEST_SIZE))
 		ret = -EINVAL;
 out:
 	kfree_sensitive(sdesc);
 	return ret;
 }
@@ -332,20 +333,20 @@ static int TSS_checkhmac2(unsigned char *buffer,
 	ret = TSS_rawhmac(testhmac1, key1, keylen1, SHA1_DIGEST_SIZE,
 			  paramdigest, TPM_NONCE_SIZE, enonce1,
 			  TPM_NONCE_SIZE, ononce, 1, continueflag1, 0, 0);
 	if (ret < 0)
 		goto out;
-	if (memcmp(testhmac1, authdata1, SHA1_DIGEST_SIZE)) {
+	if (crypto_memneq(testhmac1, authdata1, SHA1_DIGEST_SIZE)) {
 		ret = -EINVAL;
 		goto out;
 	}
 	ret = TSS_rawhmac(testhmac2, key2, keylen2, SHA1_DIGEST_SIZE,
 			  paramdigest, TPM_NONCE_SIZE, enonce2,
 			  TPM_NONCE_SIZE, ononce, 1, continueflag2, 0, 0);
 	if (ret < 0)
 		goto out;
-	if (memcmp(testhmac2, authdata2, SHA1_DIGEST_SIZE))
+	if (crypto_memneq(testhmac2, authdata2, SHA1_DIGEST_SIZE))
 		ret = -EINVAL;
 out:
 	kfree_sensitive(sdesc);
 	return ret;
 }

base-commit: d6084bb815c453de27af8071a23163a711586a6c
-- 
2.50.1