tbbr: Use constant-time bcmp() to compare hashes
To avoid timing side-channel attacks, it is needed to use a constant
time memory comparison function when comparing hashes. The affected
code only cheks for equality so it isn't needed to use any variant of
memcmp(), bcmp() is enough.
Also, timingsafe_bcmp() is as fast as memcmp() when the two compared
regions are equal, so this change incurrs no performance hit in said
case. In case they are unequal, the boot sequence wouldn't continue as
normal, so performance is not an issue.
Change-Id: I1c7c70ddfa4438e6031c8814411fef79fd3bb4df
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>
diff --git a/drivers/auth/mbedtls/mbedtls_crypto.c b/drivers/auth/mbedtls/mbedtls_crypto.c
index 1a96e8f..11d3ede 100644
--- a/drivers/auth/mbedtls/mbedtls_crypto.c
+++ b/drivers/auth/mbedtls/mbedtls_crypto.c
@@ -217,7 +217,7 @@
}
/* Compare values */
- rc = memcmp(data_hash, hash, mbedtls_md_get_size(md_info));
+ rc = timingsafe_bcmp(data_hash, hash, mbedtls_md_get_size(md_info));
if (rc != 0) {
return CRYPTO_ERR_HASH;
}
diff --git a/drivers/auth/mbedtls/mbedtls_x509_parser.c b/drivers/auth/mbedtls/mbedtls_x509_parser.c
index 73da9d1..f9485de 100644
--- a/drivers/auth/mbedtls/mbedtls_x509_parser.c
+++ b/drivers/auth/mbedtls/mbedtls_x509_parser.c
@@ -392,7 +392,7 @@
if (sig_alg1.len != sig_alg2.len) {
return IMG_PARSER_ERR_FORMAT;
}
- if (0 != memcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
+ if (0 != timingsafe_bcmp(sig_alg1.p, sig_alg2.p, sig_alg1.len)) {
return IMG_PARSER_ERR_FORMAT;
}
memcpy(&sig_alg, &sig_alg1, sizeof(sig_alg));