[PATCH v4 01/10] crypto: Provide a wrapper function for zeroizing crypto_aes_ctx

From: Thomas Huth <[email protected]>

Several crypto drivers need to zeroize their local crypto_aes_ctx
structures after use to avoid leaking key material on the stack.
Currently some call sites do this with their own memzero_explicit()
call, which is error-prone since it is easy to miss a return path
(what already happened in some drivers). Some other call sites miss
to clear crypto_aes_ctx completely.

Provide an aes_zeroize_ctx() helper that can be used with __cleanup()
to automatically zeroize the context when it goes out of scope.

Acked-by: Eric Biggers <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>
---
 include/crypto/aes.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/crypto/aes.h b/include/crypto/aes.h
index 3279cfa546085..eb970b8d623f9 100644
--- a/include/crypto/aes.h
+++ b/include/crypto/aes.h
@@ -159,6 +159,19 @@ static inline int aes_check_keylen(size_t keylen)
 int aes_expandkey(struct crypto_aes_ctx *ctx, const u8 *in_key,
 		  unsigned int key_len);
 
+/**
+ * aes_zeroize_ctx - Clear a crypto_aes_ctx structure
+ * @ctx:	The location of the context that should be zeroized
+ *
+ * Explicitly fills the crypto_aes_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 (if not using kfree_sensitive()).
+ */
+static inline void aes_zeroize_ctx(struct crypto_aes_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /*
  * The following functions are temporarily exported for use by the AES mode
  * implementations in arch/$(SRCARCH)/crypto/.  These exports will go away when
-- 
2.55.0