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Revert to not enabling asm under Memsan

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-07-31 16:54:00 +01:00
parent 378280e57f
commit 3d574da6fc
2 changed files with 9 additions and 40 deletions
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24
library/constant_time_impl.h
View File

@ -37,11 +37,18 @@
#include "mbedtls/bignum.h"
#endif
#include "../tests/include/test/constant_flow.h"
/* Disable asm under Memsan because it confuses Memsan and generates false errors */
#if defined(MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN)
#define MBEDTLS_CT_NO_ASM
#elif defined(__has_feature)
#if __has_feature(memory_sanitizer)
#define MBEDTLS_CT_NO_ASM
#endif
#endif
/* armcc5 --gnu defines __GNUC__ but doesn't support GNU's extended asm */
#if defined(MBEDTLS_HAVE_ASM) && defined(__GNUC__) && (!defined(__ARMCC_VERSION) || \
__ARMCC_VERSION >= 6000000)
__ARMCC_VERSION >= 6000000) && !defined(MBEDTLS_CT_NO_ASM)
#define MBEDTLS_CT_ASM
#if (defined(__arm__) || defined(__thumb__) || defined(__thumb2__))
#define MBEDTLS_CT_ARM_ASM
@ -84,20 +91,7 @@ extern volatile mbedtls_ct_uint_t mbedtls_ct_zero;
static inline mbedtls_ct_uint_t mbedtls_ct_compiler_opaque(mbedtls_ct_uint_t x)
{
#if defined(MBEDTLS_CT_ASM)
/* Prevent false positives from Memsan - otherwise it will report the asm as
* accessing secret data. */
TEST_CF_SAVE_SECRET(x);
asm volatile ("" : [x] "+r" (x) :);
/* Mark the return value as secret (if it was previously marked secret).
* This is needed so that code of the form:
*
* if (mbedtls_ct_compiler_opaque(secret)) { ... }
*
* will fail const-flow tests.
*/
TEST_CF_RESTORE_SECRET(x);
return x;
#else
return x ^ mbedtls_ct_zero;

25
tests/include/test/constant_flow.h
View File

@ -32,27 +32,14 @@
* #define TEST_CF_SECRET(ptr, size)
* #define TEST_CF_PUBLIC(ptr, size)
*
* and
*
* #define TEST_CF_SAVE_SECRET(variable)
* #define TEST_CF_RESTORE_SECRET(variable)
*
* 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).
*
* The SAVE/RESTORE forms mark a variable as public, and subsequently restore its
* previous secret/not-secret state. This is used where library code is generating
* false positives and needs to temporarily disable Memsan checks for a particular
* variable, and then restore it's original state afterwards so it doesn't interfere
* with other checks.
*
* Arguments:
* - ptr: a pointer to the memory area to be marked
* - size: the size in bytes of the memory area
*
* - variable: a variable name
*
* 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.
@ -76,12 +63,6 @@
#define TEST_CF_PUBLIC __msan_unpoison
// void __msan_unpoison(const volatile void *a, size_t size);
#define TEST_CF_SAVE_SECRET(_x) \
int _test_cf_is_public_ ## _x = __msan_test_shadow(&(_x), sizeof(_x)) == -1; \
TEST_CF_PUBLIC(&(_x), sizeof(_x));
#define TEST_CF_RESTORE_SECRET(_x) \
if (!_test_cf_is_public_ ## _x) TEST_CF_SECRET(&(_x), sizeof(_x));
#elif defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND)
#include <valgrind/memcheck.h>
@ -90,18 +71,12 @@
#define TEST_CF_PUBLIC VALGRIND_MAKE_MEM_DEFINED
// VALGRIND_MAKE_MEM_DEFINED(_qzz_addr, _qzz_len)
#define TEST_CF_SAVE_SECRET(_x)
#define TEST_CF_RESTORE_SECRET(_x)
#else /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN ||
MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */
#define TEST_CF_SECRET(ptr, size)
#define TEST_CF_PUBLIC(ptr, size)
#define TEST_CF_SAVE_SECRET(_x)
#define TEST_CF_RESTORE_SECRET(_x)
#endif /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN ||
MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */