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lib/crypto: aes-cmac: Add zeroization functions

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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>
Link: https://patch.msgid.link/20260807125845.1477067-2-thuth@redhat.com
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
This commit is contained in:
Thomas Huth
2026-08-07 14:58:38 +02:00
committed by Eric Biggers
parent 6d22ec2629
commit adbc4db2c0
1 changed files with 34 additions and 0 deletions
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34
include/crypto/aes-cbc-macs.h
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@@ -8,6 +8,7 @@
#define _CRYPTO_AES_CBC_MACS_H
#include <crypto/aes.h>
#include <linux/string.h>
/**
* struct aes_cmac_key - Prepared key for AES-CMAC or AES-XCBC-MAC
@@ -24,6 +25,19 @@ struct aes_cmac_key {
} k_final[2];
};
/**
* aes_cmac_zeroize_key() - Zeroize an aes_cmac_key structure
* @key: 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 (if not using kfree_sensitive()).
*/
static inline void aes_cmac_zeroize_key(struct aes_cmac_key *key)
{
memzero_explicit(key, sizeof(*key));
}
/**
* struct aes_cmac_ctx - Context for computing an AES-CMAC or AES-XCBC-MAC value
* @key: Pointer to the key struct. A pointer is used rather than a copy of the
@@ -40,6 +54,19 @@ struct aes_cmac_ctx {
u8 h[AES_BLOCK_SIZE];
};
/**
* aes_cmac_zeroize_ctx() - Zeroize an 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_preparekey() - Prepare a key for AES-CMAC
* @key: (output) The key struct to initialize
@@ -47,6 +74,10 @@ struct aes_cmac_ctx {
* @key_len: Length of the raw key in bytes. The supported values are
* AES_KEYSIZE_128, AES_KEYSIZE_192, and AES_KEYSIZE_256.
*
* On success, the caller should ensure that the prepared key is zeroized
* at the end of its lifetime, e.g. by calling aes_cmac_zeroize_key() or
* kfree_sensitive().
*
* Context: Any context.
* Return: 0 on success or -EINVAL if the given key length is invalid. No other
* errors are possible, so callers that always pass a valid key length
@@ -79,6 +110,9 @@ void aes_xcbcmac_preparekey(struct aes_cmac_key *key,
*
* This supports both AES-CMAC and AES-XCBC-MAC. Which one is done depends on
* whether aes_cmac_preparekey() or aes_xcbcmac_preparekey() was called.
*
* The caller should ensure that the context is zeroized at the end of its
* lifetime, e.g. by calling aes_cmac_final() or aes_cmac_zeroize_ctx().
*/
static inline void aes_cmac_init(struct aes_cmac_ctx *ctx,
const struct aes_cmac_key *key)