Fix asm Memsan workaround
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/constant_time_impl.h b/library/constant_time_impl.h
index c9e6a83..191769b 100644
--- a/library/constant_time_impl.h
+++ b/library/constant_time_impl.h
@@ -73,17 +73,18 @@
#if defined(MBEDTLS_CT_ASM)
/* Prevent false positives from Memsan - otherwise it will report the asm as
* accessing secret data. */
- TEST_CF_PUBLIC(&x, sizeof(x));
+ TEST_CF_SAVE_SECRET(x);
asm volatile ("" : [x] "+r" (x) :);
- /* Mark the return value as secret. This is needed so that code of the form:
+ /* 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_SECRET(&x, sizeof(x));
+ TEST_CF_RESTORE_SECRET(x);
return x;
#else
return x ^ mbedtls_ct_zero;
diff --git a/tests/include/test/constant_flow.h b/tests/include/test/constant_flow.h
index f3d676e..5728357 100644
--- a/tests/include/test/constant_flow.h
+++ b/tests/include/test/constant_flow.h
@@ -32,14 +32,27 @@
* #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.
@@ -63,6 +76,9 @@
#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) do { if (!_test_cf_is_public_ ## _x) TEST_CF_SECRET(&(_x), sizeof(_x)); } while(0)
+
#elif defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND)
#include <valgrind/memcheck.h>
@@ -71,12 +87,18 @@
#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 */