[PATCH v3 03/13] lib/crypto: aes-gcm: Provide functions for zeroizing aes_gcm* structures

[Thomas Huth <thuth@redhat.com>]

In certain cases crypto code needs to zeroize their local aes_gcm_key
or aes_gcm_ctx structures after use to avoid leaking sensitive material.
Provide aes_gcm_zeroize_key() and aes_gcm_zeroize_ctx() helper functions
that e.g. can be used with __cleanup() to automatically zeroize the
structures when they go out of scope.

While we're at it, replace the related memzero_explicit() calls in
lib/crypto/aes.c with calls to the new helper functions.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/crypto/aes-gcm.h | 22 ++++++++++++++++++++--
 lib/crypto/aes.c         |  8 +++-----
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/include/crypto/aes-gcm.h b/include/crypto/aes-gcm.h
index 2aee62f019891..a81b00fd8e27f 100644
--- a/include/crypto/aes-gcm.h
+++ b/include/crypto/aes-gcm.h
@@ -21,6 +21,15 @@ struct aes_gcm_key {
 	size_t authtag_len; /* Length of authentication tags in bytes */
 };
 
+/**
+ * aes_gcm_zeroize_key() - Zeroize an aes_gcm_key structure
+ * @key: The aes_gcm_key to zeroize
+ */
+static inline void aes_gcm_zeroize_key(struct aes_gcm_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct aes_gcm_ctx - Context for incrementally en/decrypting a message
  */
@@ -58,6 +67,15 @@ struct aes_gcm_ctx {
 	u64 data_len;
 };
 
+/**
+ * aes_gcm_zeroize_ctx() - Zeroize an aes_gcm_ctx structure
+ * @ctx: The aes_gcm_ctx to zeroize
+ */
+static inline void aes_gcm_zeroize_ctx(struct aes_gcm_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * aes_gcm_preparekey() - Prepare a key for AES-GCM encryption and decryption
  * @key: (output) The key structure to initialize
@@ -66,8 +84,8 @@ struct aes_gcm_ctx {
  * @authtag_len: Length of the authentication tag in bytes:
  *		 4, 8, 12, 13, 14, 15, or 16.  16 is recommended.
  *
- * Users should use memzero_explicit() to zeroize the key struct at the end of
- * its lifetime.  (But if this function fails, zeroization is unnecessary.)
+ * Users should use aes_gcm_zeroize_key() to zeroize the key struct at the end
+ * of its lifetime.  (But if this function fails, zeroization is unnecessary.)
  *
  * Context: Any context.
  * Return:
diff --git a/lib/crypto/aes.c b/lib/crypto/aes.c
index 34ef5deca0a79..0cb5d7355926e 100644
--- a/lib/crypto/aes.c
+++ b/lib/crypto/aes.c
@@ -1670,7 +1670,7 @@ void aes_gcm_encrypt_final(struct aes_gcm_ctx *ctx, u8 *authtag)
 	ghash_final(&ctx->ghash, ctx->ctr); /* Use ctr as temp buffer */
 
 	crypto_xor_cpy(authtag, ctx->ctr, ctx->j0_enc, ctx->key->authtag_len);
-	memzero_explicit(ctx, sizeof(*ctx));
+	aes_gcm_zeroize_ctx(ctx);
 }
 EXPORT_SYMBOL_GPL(aes_gcm_encrypt_final);
 
@@ -1697,7 +1697,7 @@ int aes_gcm_decrypt_final(struct aes_gcm_ctx *ctx, const u8 *authtag)
 		      -EBADMSG :
 		      0;
 out:
-	memzero_explicit(ctx, sizeof(*ctx));
+	aes_gcm_zeroize_ctx(ctx);
 	return err;
 }
 EXPORT_SYMBOL_GPL(aes_gcm_decrypt_final);
@@ -1742,7 +1742,7 @@ static void __init aes_gcm_fips_test(void)
 {
 	const size_t data_len = sizeof(fips_test_data);
 	u8 buf[sizeof(fips_test_data) + AES_BLOCK_SIZE];
-	struct aes_gcm_key key;
+	struct aes_gcm_key key __cleanup(aes_gcm_zeroize_key);
 	int err;
 
 	if (aes_gcm_preparekey(&key, fips_test_key, sizeof(fips_test_key),
@@ -1760,8 +1760,6 @@ static void __init aes_gcm_fips_test(void)
 		panic("aes: GCM FIPS self-test failed (decryption failed)\n");
 	if (memcmp(fips_test_data, buf, data_len) != 0)
 		panic("aes: GCM FIPS self-test failed (wrong plaintext)\n");
-
-	memzero_explicit(&key, sizeof(key));
 }
 #else /* CONFIG_CRYPTO_LIB_AES_GCM */
 static inline void aes_gcm_fips_test(void)
-- 
2.55.0