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Merge pull request #736 from mpg/cf-varpos-copy-dev-restricted

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Constant-flow copy of HMAC from variable position
This commit is contained in:
Janos Follath 2020-08-25 14:35:55 +01:00 committed by GitHub
commit d4ac4e037b
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11 changed files with 211 additions and 39 deletions
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24
include/mbedtls/config.h
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@ -1911,9 +1911,10 @@
*
* Enable testing of the constant-flow nature of some sensitive functions with
* clang's MemorySanitizer. This causes some existing tests to also test
* non-functional properties of the code under test.
* this non-functional property of the code under test.
*
* This setting requires compiling with clang -fsanitize=memory.
* This setting requires compiling with clang -fsanitize=memory. The test
* suites can then be run normally.
*
* \warning This macro is only used for extended testing; it is not considered
* part of the library's API, so it may change or disappear at any time.
@ -1922,6 +1923,25 @@
*/
//#define MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN
/**
* \def MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND
*
* Enable testing of the constant-flow nature of some sensitive functions with
* valgrind's memcheck tool. This causes some existing tests to also test
* this non-functional property of the code under test.
*
* This setting requires valgrind headers for building, and is only useful for
* testing if the tests suites are run with valgrind's memcheck. This can be
* done for an individual test suite with 'valgrind ./test_suite_xxx', or when
* using CMake, this can be done for all test suites with 'make memcheck'.
*
* \warning This macro is only used for extended testing; it is not considered
* part of the library's API, so it may change or disappear at any time.
*
* Uncomment to enable testing of the constant-flow nature of selected code.
*/
//#define MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND
/**
* \def MBEDTLS_TEST_HOOKS
*

24
library/ssl_invasive.h
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@ -71,6 +71,30 @@ int mbedtls_ssl_cf_hmac(
const unsigned char *data, size_t data_len_secret,
size_t min_data_len, size_t max_data_len,
unsigned char *output );
/** \brief Copy data from a secret position with constant flow.
*
* This function copies \p len bytes from \p src_base + \p offset_secret to \p
* dst, with a code flow and memory access pattern that does not depend on \p
* offset_secret, but only on \p offset_min, \p offset_max and \p len.
*
* \param dst The destination buffer. This must point to a writable
* buffer of at least \p len bytes.
* \param src_base The base of the source buffer. This must point to a
* readable buffer of at least \p offset_max + \p len
* bytes.
* \param offset_secret The offset in the source buffer from which to copy.
* This must be no less than \p offset_min and no greater
* than \p offset_max.
* \param offset_min The minimal value of \p offset_secret.
* \param offset_max The maximal value of \p offset_secret.
* \param len The number of bytes to copy.
*/
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 );
#endif /* MBEDTLS_TEST_HOOKS && MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
#endif /* MBEDTLS_SSL_INVASIVE_H */

60
library/ssl_msg.c
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@ -312,27 +312,6 @@ int (*mbedtls_ssl_hw_record_read)( mbedtls_ssl_context *ssl ) = NULL;
int (*mbedtls_ssl_hw_record_finish)( mbedtls_ssl_context *ssl ) = NULL;
#endif /* MBEDTLS_SSL_HW_RECORD_ACCEL */
/* The function below is only used in the Lucky 13 counter-measure in
* mbedtls_ssl_decrypt_buf(). These are the defines that guard the call site. */
#if defined(MBEDTLS_SSL_SOME_MODES_USE_MAC) && \
( defined(MBEDTLS_SSL_PROTO_TLS1) || \
defined(MBEDTLS_SSL_PROTO_TLS1_1) || \
defined(MBEDTLS_SSL_PROTO_TLS1_2) )
/* This function makes sure every byte in the memory region is accessed
* (in ascending addresses order) */
static void ssl_read_memory( const unsigned char *p, size_t len )
{
unsigned char acc = 0;
volatile unsigned char force;
for( ; len != 0; p++, len-- )
acc ^= *p;
force = acc;
(void) force;
}
#endif /* SSL_SOME_MODES_USE_MAC && ( TLS1 || TLS1_1 || TLS1_2 ) */
/*
* Encryption/decryption functions
*/
@ -1191,6 +1170,27 @@ 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 independent 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 )
{
size_t offset;
for( offset = offset_min; offset <= offset_max; offset++ )
{
mbedtls_ssl_cf_memcpy_if_eq( dst, src_base + offset, len,
offset, offset_secret );
}
}
#endif /* MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC */
int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
@ -1635,6 +1635,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
if( auth_done == 0 )
{
unsigned char mac_expect[MBEDTLS_SSL_MAC_ADD];
unsigned char mac_peer[MBEDTLS_SSL_MAC_ADD];
/* If the initial value of padlen was such that
* data_len < maclen + padlen + 1, then padlen
@ -1661,6 +1662,7 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
data, rec->data_len,
rec->ctr, rec->type,
mac_expect );
memcpy( mac_peer, data + rec->data_len, transform->maclen );
}
else
#endif /* MBEDTLS_SSL_PROTO_SSL3 */
@ -1670,7 +1672,7 @@ 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.
@ -1691,12 +1693,10 @@ 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 );
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 || \
@ -1708,10 +1708,10 @@ int mbedtls_ssl_decrypt_buf( mbedtls_ssl_context const *ssl,
#if defined(MBEDTLS_SSL_DEBUG_ALL)
MBEDTLS_SSL_DEBUG_BUF( 4, "expected mac", mac_expect, transform->maclen );
MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", data + rec->data_len, transform->maclen );
MBEDTLS_SSL_DEBUG_BUF( 4, "message mac", mac_peer, transform->maclen );
#endif
if( mbedtls_ssl_safer_memcmp( data + rec->data_len, mac_expect,
if( mbedtls_ssl_safer_memcmp( mac_peer, mac_expect,
transform->maclen ) != 0 )
{
#if defined(MBEDTLS_SSL_DEBUG_ALL)

3
library/version_features.c
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@ -558,6 +558,9 @@ static const char * const features[] = {
#if defined(MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN)
"MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN",
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN */
#if defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND)
"MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND",
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */
#if defined(MBEDTLS_TEST_HOOKS)
"MBEDTLS_TEST_HOOKS",
#endif /* MBEDTLS_TEST_HOOKS */

8
programs/test/query_config.c
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@ -1544,6 +1544,14 @@ int query_config( const char *config )
}
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN */
#if defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND)
if( strcmp( "MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND", config ) == 0 )
{
MACRO_EXPANSION_TO_STR( MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND );
return( 0 );
}
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */
#if defined(MBEDTLS_TEST_HOOKS)
if( strcmp( "MBEDTLS_TEST_HOOKS", config ) == 0 )
{

1
scripts/config.py
View File

@ -193,6 +193,7 @@ EXCLUDE_FROM_FULL = frozenset([
'MBEDTLS_SHA512_NO_SHA384', # removes a feature
'MBEDTLS_SSL_HW_RECORD_ACCEL', # build dependency (hook functions)
'MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN', # build dependency (clang+memsan)
'MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND', # build dependency (valgrind headers)
'MBEDTLS_TEST_NULL_ENTROPY', # removes a feature
'MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION', # influences the use of X.509 in TLS
'MBEDTLS_ZLIB_SUPPORT', # build dependency (libz)

36
tests/include/test/constant_flow.h
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@ -30,6 +30,28 @@
#include MBEDTLS_CONFIG_FILE
#endif
/*
* This file defines the two macros
*
* #define TEST_CF_SECRET(ptr, size)
* #define TEST_CF_PUBLIC(ptr, size)
*
* that can be used in tests to mark a memory area as secret (no branch or
* memory access should depend on it) or public (default, only needs to be
* marked explicitly when it was derived from secret data).
*
* Arguments:
* - ptr: a pointer to the memory area to be marked
* - size: the size in bytes of the memory area
*
* Implementation:
* The basic idea is that of ctgrind <https://github.com/agl/ctgrind>: we can
* re-use tools that were designed for checking use of uninitialized memory.
* This file contains two implementations: one based on MemorySanitizer, the
* other on valgrind's memcheck. If none of them is enabled, dummy macros that
* do nothing are defined for convenience.
*/
#if defined(MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN)
#include <sanitizer/msan_interface.h>
@ -39,11 +61,21 @@
#define TEST_CF_PUBLIC __msan_unpoison
// void __msan_unpoison(const volatile void *a, size_t size);
#else /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN */
#elif defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND)
#include <valgrind/memcheck.h>
#define TEST_CF_SECRET VALGRIND_MAKE_MEM_UNDEFINED
// VALGRIND_MAKE_MEM_UNDEFINED(_qzz_addr, _qzz_len)
#define TEST_CF_PUBLIC VALGRIND_MAKE_MEM_DEFINED
// VALGRIND_MAKE_MEM_DEFINED(_qzz_addr, _qzz_len)
#else /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN ||
MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */
#define TEST_CF_SECRET(ptr, size)
#define TEST_CF_PUBLIC(ptr, size)
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN */
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN ||
MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */
#endif /* TEST_CONSTANT_FLOW_H */

22
tests/scripts/all.sh
View File

@ -1109,6 +1109,28 @@ component_test_memsan_constant_flow () {
make test
}
component_test_valgrind_constant_flow () {
# This tests both (1) everything that valgrind's memcheck usually checks
# (heap buffer overflows, use of uninitialized memory, use-after-free,
# etc.) and (2) branches or memory access depending on secret values,
# which will be reported as uninitialized memory. To distinguish between
# secret and actually uninitialized:
# - unset MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND - does the failure persist?
# - or alternatively, build with debug info and manually run the offending
# test suite with valgrind --track-origins=yes, then check if the origin
# was TEST_CF_SECRET() or something else.
msg "build: cmake release GCC, full config with constant flow testing"
scripts/config.py full
scripts/config.py set MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND
cmake -D CMAKE_BUILD_TYPE:String=Release .
make
# this only shows a summary of the results (how many of each type)
# details are left in Testing/<date>/DynamicAnalysis.xml
msg "test: main suites (valgrind + constant flow)"
make memcheck
}
component_test_default_no_deprecated () {
# Test that removing the deprecated features from the default
# configuration leaves something consistent.

12
tests/suites/test_suite_ssl.data
View File

@ -10545,3 +10545,15 @@ ssl_cf_hmac:MBEDTLS_MD_SHA256
Constant-flow HMAC: SHA384
depends_on:MBEDTLS_SHA512_C:!MBEDTLS_SHA512_NO_SHA384
ssl_cf_hmac:MBEDTLS_MD_SHA384
# these are the numbers we'd get with an empty plaintext and truncated HMAC
Constant-flow memcpy from offset: small
ssl_cf_memcpy_offset:0:5:10
# we could get this with 255-bytes plaintext and untruncated SHA-256
Constant-flow memcpy from offset: medium
ssl_cf_memcpy_offset:0:255:32
# we could get this with 255-bytes plaintext and untruncated SHA-384
Constant-flow memcpy from offset: large
ssl_cf_memcpy_offset:100:339:48

33
tests/suites/test_suite_ssl.function
View File

@ -4361,3 +4361,36 @@ exit:
mbedtls_free( out );
}
/* END_CASE */
/* BEGIN_CASE depends_on:MBEDTLS_SSL_SOME_SUITES_USE_TLS_CBC:MBEDTLS_TEST_HOOKS */
void ssl_cf_memcpy_offset( int offset_min, int offset_max, int len )
{
unsigned char *dst = NULL;
unsigned char *src = NULL;
size_t src_len = offset_max + len;
size_t secret;
ASSERT_ALLOC( dst, len );
ASSERT_ALLOC( src, src_len );
/* Fill src in a way that we can detect if we copied the right bytes */
mbedtls_test_rnd_std_rand( NULL, src, src_len );
for( secret = offset_min; secret <= (size_t) offset_max; secret++ )
{
test_set_step( (int) secret );
TEST_CF_SECRET( &secret, sizeof( secret ) );
mbedtls_ssl_cf_memcpy_offset( dst, src, secret,
offset_min, offset_max, len );
TEST_CF_PUBLIC( &secret, sizeof( secret ) );
TEST_CF_PUBLIC( dst, len );
ASSERT_COMPARE( dst, len, src + secret, len );
}
exit:
mbedtls_free( dst );
mbedtls_free( src );
}
/* END_CASE */

27
tests/suites/test_suite_x509write.function
View File

@ -5,11 +5,25 @@
#include "mbedtls/pem.h"
#include "mbedtls/oid.h"
#include "mbedtls/rsa.h"
#if defined(MBEDTLS_USE_PSA_CRYPTO)
/* These are the same depends as the test function x509_crs_check_opaque(),
* the only function using PSA here. Using a weaker condition would result in
* warnings about the static functions defined in psa_crypto_helpers.h being
* unused. */
#if defined(MBEDTLS_USE_PSA_CRYPTO) && \
defined(MBEDTLS_PEM_WRITE_C) && \
defined(MBEDTLS_X509_CSR_WRITE_C)
#include "psa/crypto.h"
#include "mbedtls/psa_util.h"
#endif
#include "test/psa_crypto_helpers.h"
#define PSA_INIT( ) PSA_ASSERT( psa_crypto_init( ) )
#else
/* Define empty macros so that we can use them in the preamble and teardown
* of every test function that uses PSA conditionally based on
* MBEDTLS_USE_PSA_CRYPTO. */
#define PSA_INIT( ) ( (void) 0 )
#define PSA_DONE( ) ( (void) 0 )
#endif /* MBEDTLS_USE_PSA_CRYPTO && MBEDTLS_PEM_WRITE_C && MBEDTLS_X509_CSR_WRITE_C */
#if defined(MBEDTLS_RSA_C)
int mbedtls_rsa_decrypt_func( void *ctx, int mode, size_t *olen,
@ -147,7 +161,7 @@ void x509_csr_check_opaque( char *key_file, int md_type, int key_usage,
int cert_type )
{
mbedtls_pk_context key;
psa_key_handle_t slot;
psa_key_handle_t slot = 0;
psa_algorithm_t md_alg_psa;
mbedtls_x509write_csr req;
unsigned char buf[4096];
@ -156,7 +170,7 @@ void x509_csr_check_opaque( char *key_file, int md_type, int key_usage,
const char *subject_name = "C=NL,O=PolarSSL,CN=PolarSSL Server 1";
mbedtls_test_rnd_pseudo_info rnd_info;
psa_crypto_init();
PSA_INIT( );
memset( &rnd_info, 0x2a, sizeof( mbedtls_test_rnd_pseudo_info ) );
md_alg_psa = mbedtls_psa_translate_md( (mbedtls_md_type_t) md_type );
@ -184,9 +198,12 @@ void x509_csr_check_opaque( char *key_file, int md_type, int key_usage,
buf[pem_len] = '\0';
TEST_ASSERT( x509_crt_verifycsr( buf, pem_len + 1 ) == 0 );
exit:
mbedtls_x509write_csr_free( &req );
mbedtls_pk_free( &key );
psa_destroy_key( slot );
PSA_DONE( );
}
/* END_CASE */