[PATCH v2 1/6] crypto: Use memzero_explicit() for clearing state

Arvind Sankar
2020-10-20T20:40:26Z

Without the barrier_data() inside memzero_explicit(), the compiler may
optimize away the state-clearing if it can tell that the state is not
used afterwards. At least in lib/crypto/sha256.c:__sha256_final(), the
function can get inlined into sha256(), in which case the memset is
optimized away.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
include/crypto/sha1_base.h | 3 ++-
include/crypto/sha256_base.h | 3 ++-
include/crypto/sha512_base.h | 3 ++-
include/crypto/sm3_base.h | 3 ++-
lib/crypto/sha256.c | 2 +-
5 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/include/crypto/sha1_base.h b/include/crypto/sha1_base.h
index 20fd1f7468af..a5d6033efef7 100644
--- a/include/crypto/sha1_base.h
+++ b/include/crypto/sha1_base.h
@@ -12,6 +12,7 @@
#include <crypto/sha.h>
#include <linux/crypto.h>
#include <linux/module.h>
+#include <linux/string.h>

#include <asm/unaligned.h>

@@ -101,7 +102,7 @@ static inline int sha1_base_finish(struct shash_desc *desc, u8 *out)
for (i = 0; i < SHA1_DIGEST_SIZE / sizeof(__be32); i++)
put_unaligned_be32(sctx->state[i], digest++);

- *sctx = (struct sha1_state){};
+ memzero_explicit(sctx, sizeof(*sctx));
return 0;
}

diff --git a/include/crypto/sha256_base.h b/include/crypto/sha256_base.h
index 6ded110783ae..93f9fd21cc06 100644
--- a/include/crypto/sha256_base.h
+++ b/include/crypto/sha256_base.h
@@ -12,6 +12,7 @@
#include <crypto/sha.h>
#include <linux/crypto.h>
#include <linux/module.h>
+#include <linux/string.h>

#include <asm/unaligned.h>

@@ -105,7 +106,7 @@ static inline int sha256_base_finish(struct shash_desc *desc, u8 *out)
for (i = 0; digest_size > 0; i++, digest_size -= sizeof(__be32))
put_unaligned_be32(sctx->state[i], digest++);

- *sctx = (struct sha256_state){};
+ memzero_explicit(sctx, sizeof(*sctx));
return 0;
}

diff --git a/include/crypto/sha512_base.h b/include/crypto/sha512_base.h
index fb19c77494dc..93ab73baa38e 100644
--- a/include/crypto/sha512_base.h
+++ b/include/crypto/sha512_base.h
@@ -12,6 +12,7 @@
#include <crypto/sha.h>
#include <linux/crypto.h>
#include <linux/module.h>
+#include <linux/string.h>

#include <asm/unaligned.h>

@@ -126,7 +127,7 @@ static inline int sha512_base_finish(struct shash_desc *desc, u8 *out)
for (i = 0; digest_size > 0; i++, digest_size -= sizeof(__be64))
put_unaligned_be64(sctx->state[i], digest++);

- *sctx = (struct sha512_state){};
+ memzero_explicit(sctx, sizeof(*sctx));
return 0;
}

diff --git a/include/crypto/sm3_base.h b/include/crypto/sm3_base.h
index 1cbf9aa1fe52..2f3a32ab97bb 100644
--- a/include/crypto/sm3_base.h
+++ b/include/crypto/sm3_base.h
@@ -13,6 +13,7 @@
#include <crypto/sm3.h>
#include <linux/crypto.h>
#include <linux/module.h>
+#include <linux/string.h>
#include <asm/unaligned.h>

typedef void (sm3_block_fn)(struct sm3_state *sst, u8 const *src, int blocks);
@@ -104,7 +105,7 @@ static inline int sm3_base_finish(struct shash_desc *desc, u8 *out)
for (i = 0; i < SM3_DIGEST_SIZE / sizeof(__be32); i++)
put_unaligned_be32(sctx->state[i], digest++);

- *sctx = (struct sm3_state){};
+ memzero_explicit(sctx, sizeof(*sctx));
return 0;
}

diff --git a/lib/crypto/sha256.c b/lib/crypto/sha256.c
index 2321f6cb322f..d43bc39ab05e 100644
--- a/lib/crypto/sha256.c
+++ b/lib/crypto/sha256.c
@@ -265,7 +265,7 @@ static void __sha256_final(struct sha256_state *sctx, u8 *out, int digest_words)
put_unaligned_be32(sctx->state[i], &dst[i]);

/* Zeroize sensitive information. */
- memset(sctx, 0, sizeof(*sctx));
+ memzero_explicit(sctx, sizeof(*sctx));
}

void sha256_final(struct sha256_state *sctx, u8 *out)
--
2.26.2