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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
2020-08-18 12:02:54 +02:00
parent 3c31afaca6
commit 7fe2c5f086
4 changed files with 92 additions and 8 deletions
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31
library/ssl_msg.c
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@ -1193,6 +1193,24 @@ 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.
*/
MBEDTLS_STATIC_TESTABLE 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 */
int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
@ -1674,7 +1692,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
{
/*
* The next two sizes are the minimum and maximum values of
* in_msglen over all padlen values.
* data_len over all padlen values.
*
* They're independent of padlen, since we previously did
* data_len -= padlen.
@ -1695,13 +1713,10 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *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( data + min_len,
max_len - min_len + transform->maclen );
memcpy( mac_peer, data + rec->data_len, transform->maclen );
mbedtls_ssl_cf_memcpy_offset( mac_peer, data,
rec->data_len,
min_len, max_len,
transform->maclen );
}
else
#endif /* MBEDTLS_SSL_PROTO_TLS1 || MBEDTLS_SSL_PROTO_TLS1_1 || \