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authorCesar Eduardo Barros <cesarb@cesarb.eti.br>2013-11-25 22:00:41 -0200
committerHerbert Xu <herbert@gondor.apana.org.au>2013-12-05 21:28:41 +0800
commitfe8c8a126806fea4465c43d62a1f9d273a572bf5 (patch)
treeea40ae4afce934575065383d1de44d04cd6490fc /crypto/memneq.c
parentb62ffd8c72c2f04ac737ef3ff0f7ba37d2013633 (diff)
downloadlinux-stericsson-fe8c8a126806fea4465c43d62a1f9d273a572bf5.tar.gz
crypto: more robust crypto_memneq
Disabling compiler optimizations can be fragile, since a new optimization could be added to -O0 or -Os that breaks the assumptions the code is making. Instead of disabling compiler optimizations, use a dummy inline assembly (based on RELOC_HIDE) to block the problematic kinds of optimization, while still allowing other optimizations to be applied to the code. The dummy inline assembly is added after every OR, and has the accumulator variable as its input and output. The compiler is forced to assume that the dummy inline assembly could both depend on the accumulator variable and change the accumulator variable, so it is forced to compute the value correctly before the inline assembly, and cannot assume anything about its value after the inline assembly. This change should be enough to make crypto_memneq work correctly (with data-independent timing) even if it is inlined at its call sites. That can be done later in a followup patch. Compile-tested on x86_64. Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.eti.br> Acked-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto/memneq.c')
-rw-r--r--crypto/memneq.c79
1 files changed, 54 insertions, 25 deletions
diff --git a/crypto/memneq.c b/crypto/memneq.c
index cd0162221c14..570f6f3401ce 100644
--- a/crypto/memneq.c
+++ b/crypto/memneq.c
@@ -72,6 +72,7 @@ __crypto_memneq_generic(const void *a, const void *b, size_t size)
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
while (size >= sizeof(unsigned long)) {
neq |= *(unsigned long *)a ^ *(unsigned long *)b;
+ OPTIMIZER_HIDE_VAR(neq);
a += sizeof(unsigned long);
b += sizeof(unsigned long);
size -= sizeof(unsigned long);
@@ -79,6 +80,7 @@ __crypto_memneq_generic(const void *a, const void *b, size_t size)
#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
while (size > 0) {
neq |= *(unsigned char *)a ^ *(unsigned char *)b;
+ OPTIMIZER_HIDE_VAR(neq);
a += 1;
b += 1;
size -= 1;
@@ -89,33 +91,60 @@ __crypto_memneq_generic(const void *a, const void *b, size_t size)
/* Loop-free fast-path for frequently used 16-byte size */
static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
{
+ unsigned long neq = 0;
+
#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
- if (sizeof(unsigned long) == 8)
- return ((*(unsigned long *)(a) ^ *(unsigned long *)(b))
- | (*(unsigned long *)(a+8) ^ *(unsigned long *)(b+8)));
- else if (sizeof(unsigned int) == 4)
- return ((*(unsigned int *)(a) ^ *(unsigned int *)(b))
- | (*(unsigned int *)(a+4) ^ *(unsigned int *)(b+4))
- | (*(unsigned int *)(a+8) ^ *(unsigned int *)(b+8))
- | (*(unsigned int *)(a+12) ^ *(unsigned int *)(b+12)));
- else
+ if (sizeof(unsigned long) == 8) {
+ neq |= *(unsigned long *)(a) ^ *(unsigned long *)(b);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned long *)(a+8) ^ *(unsigned long *)(b+8);
+ OPTIMIZER_HIDE_VAR(neq);
+ } else if (sizeof(unsigned int) == 4) {
+ neq |= *(unsigned int *)(a) ^ *(unsigned int *)(b);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned int *)(a+4) ^ *(unsigned int *)(b+4);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned int *)(a+8) ^ *(unsigned int *)(b+8);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned int *)(a+12) ^ *(unsigned int *)(b+12);
+ OPTIMIZER_HIDE_VAR(neq);
+ } else {
#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
- return ((*(unsigned char *)(a) ^ *(unsigned char *)(b))
- | (*(unsigned char *)(a+1) ^ *(unsigned char *)(b+1))
- | (*(unsigned char *)(a+2) ^ *(unsigned char *)(b+2))
- | (*(unsigned char *)(a+3) ^ *(unsigned char *)(b+3))
- | (*(unsigned char *)(a+4) ^ *(unsigned char *)(b+4))
- | (*(unsigned char *)(a+5) ^ *(unsigned char *)(b+5))
- | (*(unsigned char *)(a+6) ^ *(unsigned char *)(b+6))
- | (*(unsigned char *)(a+7) ^ *(unsigned char *)(b+7))
- | (*(unsigned char *)(a+8) ^ *(unsigned char *)(b+8))
- | (*(unsigned char *)(a+9) ^ *(unsigned char *)(b+9))
- | (*(unsigned char *)(a+10) ^ *(unsigned char *)(b+10))
- | (*(unsigned char *)(a+11) ^ *(unsigned char *)(b+11))
- | (*(unsigned char *)(a+12) ^ *(unsigned char *)(b+12))
- | (*(unsigned char *)(a+13) ^ *(unsigned char *)(b+13))
- | (*(unsigned char *)(a+14) ^ *(unsigned char *)(b+14))
- | (*(unsigned char *)(a+15) ^ *(unsigned char *)(b+15)));
+ neq |= *(unsigned char *)(a) ^ *(unsigned char *)(b);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+1) ^ *(unsigned char *)(b+1);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+2) ^ *(unsigned char *)(b+2);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+3) ^ *(unsigned char *)(b+3);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+4) ^ *(unsigned char *)(b+4);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+5) ^ *(unsigned char *)(b+5);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+6) ^ *(unsigned char *)(b+6);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+7) ^ *(unsigned char *)(b+7);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+8) ^ *(unsigned char *)(b+8);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+9) ^ *(unsigned char *)(b+9);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+10) ^ *(unsigned char *)(b+10);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+11) ^ *(unsigned char *)(b+11);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+12) ^ *(unsigned char *)(b+12);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+13) ^ *(unsigned char *)(b+13);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+14) ^ *(unsigned char *)(b+14);
+ OPTIMIZER_HIDE_VAR(neq);
+ neq |= *(unsigned char *)(a+15) ^ *(unsigned char *)(b+15);
+ OPTIMIZER_HIDE_VAR(neq);
+ }
+
+ return neq;
}
/* Compare two areas of memory without leaking timing information,