[PATCH 2/3] lib/crypto: sha2: Provide functions for zeroizing SHA2 hmac_sha* structures

[Thomas Huth <thuth@redhat.com>]

In certain cases crypto code functions need to zeroize their local SHA2
hmac_sha*_key or hmac_sha*_ctx structures after use to avoid leaking
sensitive material on the stack.
Provide hmac_sha*_zeroize_key() and hmac_sha*_zeroize_ctx() helper
functions that can be used with __cleanup() to automatically zeroize
the structure when it goes out of scope.

Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 include/crypto/sha2.h | 73 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/include/crypto/sha2.h b/include/crypto/sha2.h
index 7bb8fe169daf2..22fbc37ae8407 100644
--- a/include/crypto/sha2.h
+++ b/include/crypto/sha2.h
@@ -7,6 +7,7 @@
 #define _CRYPTO_SHA2_H
 
 #include <linux/types.h>
+#include <linux/string.h>
 
 #define SHA224_DIGEST_SIZE	28
 #define SHA224_BLOCK_SIZE	64
@@ -210,6 +211,15 @@ struct hmac_sha224_key {
 	struct __hmac_sha256_key key;
 };
 
+/**
+ * hmac_sha224_zeroize_key() - Zeroize an hmac_sha224_key structure
+ * @key: The hmac_sha224_key to zeroize
+ */
+static inline void hmac_sha224_zeroize_key(struct hmac_sha224_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct hmac_sha224_ctx - Context for computing HMAC-SHA224 of a message
  * @ctx: private
@@ -218,6 +228,15 @@ struct hmac_sha224_ctx {
 	struct __hmac_sha256_ctx ctx;
 };
 
+/**
+ * hmac_sha224_zeroize_ctx() - Zeroize an hmac_sha224_ctx structure
+ * @ctx: The hmac_sha224_ctx context to zeroize
+ */
+static inline void hmac_sha224_zeroize_ctx(struct hmac_sha224_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * hmac_sha224_preparekey() - Prepare a key for HMAC-SHA224
  * @key: (output) the key structure to initialize
@@ -414,6 +433,15 @@ struct hmac_sha256_key {
 	struct __hmac_sha256_key key;
 };
 
+/**
+ * hmac_sha256_zeroize_key() - Zeroize an hmac_sha256_key structure
+ * @key: The hmac_sha256_key to zeroize
+ */
+static inline void hmac_sha256_zeroize_key(struct hmac_sha256_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct hmac_sha256_ctx - Context for computing HMAC-SHA256 of a message
  * @ctx: private
@@ -422,6 +450,15 @@ struct hmac_sha256_ctx {
 	struct __hmac_sha256_ctx ctx;
 };
 
+/**
+ * hmac_sha256_zeroize_ctx() - Zeroize an hmac_sha256_ctx structure
+ * @ctx: The hmac_sha256_ctx context to zeroize
+ */
+static inline void hmac_sha256_zeroize_ctx(struct hmac_sha256_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * hmac_sha256_preparekey() - Prepare a key for HMAC-SHA256
  * @key: (output) the key structure to initialize
@@ -623,6 +660,15 @@ struct hmac_sha384_key {
 	struct __hmac_sha512_key key;
 };
 
+/**
+ * hmac_sha384_zeroize_key() - Zeroize an hmac_sha384_key structure
+ * @key: The hmac_sha384_key to zeroize
+ */
+static inline void hmac_sha384_zeroize_key(struct hmac_sha384_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct hmac_sha384_ctx - Context for computing HMAC-SHA384 of a message
  * @ctx: private
@@ -631,6 +677,15 @@ struct hmac_sha384_ctx {
 	struct __hmac_sha512_ctx ctx;
 };
 
+/**
+ * hmac_sha384_zeroize_ctx() - Zeroize an hmac_sha384_ctx structure
+ * @ctx: The hmac_sha384_ctx context to zeroize
+ */
+static inline void hmac_sha384_zeroize_ctx(struct hmac_sha384_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * hmac_sha384_preparekey() - Prepare a key for HMAC-SHA384
  * @key: (output) the key structure to initialize
@@ -798,6 +853,15 @@ struct hmac_sha512_key {
 	struct __hmac_sha512_key key;
 };
 
+/**
+ * hmac_sha512_zeroize_key() - Zeroize an hmac_sha512_key structure
+ * @key: The hmac_sha512_key to zeroize
+ */
+static inline void hmac_sha512_zeroize_key(struct hmac_sha512_key *key)
+{
+	memzero_explicit(key, sizeof(*key));
+}
+
 /**
  * struct hmac_sha512_ctx - Context for computing HMAC-SHA512 of a message
  * @ctx: private
@@ -806,6 +870,15 @@ struct hmac_sha512_ctx {
 	struct __hmac_sha512_ctx ctx;
 };
 
+/**
+ * hmac_sha512_zeroize_ctx() - Zeroize an hmac_sha512_ctx structure
+ * @ctx: The hmac_sha512_ctx context to zeroize
+ */
+static inline void hmac_sha512_zeroize_ctx(struct hmac_sha512_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 /**
  * hmac_sha512_preparekey() - Prepare a key for HMAC-SHA512
  * @key: (output) the key structure to initialize
-- 
2.55.0