[PATCH 1/6] crypto: Provide wrapper functions for zeroizing aes_cmac_key and aes_cmac_ctx

[Thomas Huth <thuth@redhat.com>]

From: Thomas Huth <thuth@redhat.com>

Code that uses AES-CMAC might need to zeroize their local aes_cmac_key
and/or aes_cmac_ctx structures after use to avoid leaking sensitive
material on the stack.

Provide an aes_cmac_zeroize_key() and an aes_cmac_zeroize_ctx() helper
function that can be used with __cleanup() to automatically clear
the key and context when they go out of scope.

Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/crypto/aes-cbc-macs.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/crypto/aes-cbc-macs.h b/include/crypto/aes-cbc-macs.h
index e61df108b926d..b2f3b8be7886b 100644
--- a/include/crypto/aes-cbc-macs.h
+++ b/include/crypto/aes-cbc-macs.h
@@ -109,6 +109,32 @@ void aes_cmac_update(struct aes_cmac_ctx *ctx, const u8 *data, size_t data_len);
  */
 void aes_cmac_final(struct aes_cmac_ctx *ctx, u8 out[at_least AES_BLOCK_SIZE]);
 
+/**
+ * aes_cmac_zeroize_key - Clear a aes_cmac_key structure
+ * @ctx: The location of the key structure that should be zeroized
+ *
+ * Explicitly fills the aes_cmac_key with zeroes. This should be done once
+ * the key is not required anymore to avoid that its contents are leaked
+ * on the stack or heap.
+ */
+static inline void aes_cmac_zeroize_key(struct aes_cmac_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
+/**
+ * aes_cmac_zeroize_ctx - Clear a aes_cmac_ctx structure
+ * @ctx: The location of the context that should be zeroized
+ *
+ * Explicitly fills the aes_cmac_ctx with zeroes. This should be done once
+ * the context is not required anymore to avoid that its contents are
+ * leaked on the stack or heap. Only required if not using aes_cmac_final().
+ */
+static inline void aes_cmac_zeroize_ctx(struct aes_cmac_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * aes_cmac() - Compute AES-CMAC or AES-XCBC-MAC in one shot
  * @key: The key to use
-- 
2.55.0