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Add mbedtls_ssl_cf_memcpy_offset() with tests

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The tests are supposed to be failing now (in all.sh component
test_memsan_constant_flow), but they don't as apparently MemSan doesn't
complain when the src argument of memcpy() is uninitialized, see
https://github.com/google/sanitizers/issues/1296

The next commit will add an option to test constant flow with valgrind, which
will hopefully correctly flag the current non-constant-flow implementation.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
This commit is contained in:
Manuel Pégourié-Gonnard 2020-08-25 11:18:11 +02:00
parent ce45d1a759
commit 590b2d9614
4 changed files with 90 additions and 8 deletions
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29
library/ssl_tls.c
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@ -1931,6 +1931,23 @@ cleanup:
mbedtls_md_free( &aux );
return( ret );
}
/*
* Constant-flow memcpy from variable position in buffer.
* - functionally equivalent to memcpy(dst, src + offset_secret, len)
* - but with execution flow independant from the value of offset_secret.
*/
void mbedtls_ssl_cf_memcpy_offset( unsigned char *dst,
const unsigned char *src_base,
size_t offset_secret,
size_t offset_min, size_t offset_max,
size_t len )
{
/* WIP - THIS IS NOT ACTUALLY CONSTANT-FLOW!
* This is just to be able to write tests and check they work. */
ssl_read_memory( src_base + offset_min, offset_max - offset_min + len );
memcpy( dst, src_base + offset_secret, len );
}
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
@ -2374,14 +2391,10 @@ static int ssl_decrypt_buf( mbedtls_ssl_context *ssl )
return( ret );
}
/* Make sure we access all the memory that could contain the MAC,
* before we check it in the next code block. This makes the
* synchronisation requirements for just-in-time Prime+Probe
* attacks much tighter and hopefully impractical. */
ssl_read_memory( ssl->in_msg + min_len,
max_len - min_len + ssl->transform_in->maclen );
memcpy( mac_peer, ssl->in_msg + ssl->in_msglen,
ssl->transform_in->maclen );
mbedtls_ssl_cf_memcpy_offset( mac_peer, ssl->in_msg,
ssl->in_msglen,
min_len, max_len,
ssl->transform_in->maclen );
}
else
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \