Document and test that memcpy_if may have src == dest
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/library/constant_time_internal.h b/library/constant_time_internal.h
index 09de92f..0cb3f2a 100644
--- a/library/constant_time_internal.h
+++ b/library/constant_time_internal.h
@@ -417,9 +417,11 @@
*
* \param condition The condition
* \param dest Secret. Destination pointer.
- * \param src1 Secret. Pointer to copy from (if \p condition == MBEDTLS_CT_TRUE). Shouldn't overlap with \p dest.
+ * \param src1 Secret. Pointer to copy from (if \p condition == MBEDTLS_CT_TRUE).
+ * This may be equal to \p dest, but may not overlap in other ways.
* \param src2 Secret (contents only - may branch to test if src2 == NULL).
- * Pointer to copy from (if \p condition == MBEDTLS_CT_FALSE and \p src2 is not NULL). Shouldn't overlap with \p dest. May be NULL.
+ * Pointer to copy from (if \p condition == MBEDTLS_CT_FALSE and \p src2 is not NULL). May be NULL.
+ * This may be equal to \p dest, but may not overlap it in other ways. It may overlap with \p src1.
* \param len Number of bytes to copy.
*/
void mbedtls_ct_memcpy_if(mbedtls_ct_condition_t condition,
@@ -450,7 +452,7 @@
* buffer of at least \p len bytes.
* \param src Secret. The base of the source buffer. This must point to a
* readable buffer of at least \p offset_max + \p len
- * bytes. Shouldn't overlap with \p dest.
+ * bytes. Shouldn't overlap with \p dest
* \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.
diff --git a/tests/suites/test_suite_constant_time.function b/tests/suites/test_suite_constant_time.function
index ac4dd7a..2fafa94 100644
--- a/tests/suites/test_suite_constant_time.function
+++ b/tests/suites/test_suite_constant_time.function
@@ -224,6 +224,7 @@
ASSERT_ALLOC(result, size + offset);
ASSERT_ALLOC(expected, size + offset);
+ /* Apply offset to result only */
for (int i = 0; i < size + offset; i++) {
src[i] = 1;
result[i] = 0xff;
@@ -243,6 +244,8 @@
ASSERT_COMPARE(expected, size, result + offset, size);
+
+ /* Apply offset to src only */
for (int i = 0; i < size + offset; i++) {
src[i] = 1;
result[i] = 0xff;
@@ -261,6 +264,8 @@
ASSERT_COMPARE(expected, size, result, size);
+
+ /* Apply offset to src and src2 */
for (int i = 0; i < size + offset; i++) {
src[i] = 1;
src2[i] = 2;
@@ -281,6 +286,25 @@
TEST_CF_PUBLIC(result, size + offset);
ASSERT_COMPARE(expected, size, result, size);
+
+
+ /* result == src == dest */
+ for (int i = 0; i < size + offset; i++) {
+ src[i] = 2;
+ expected[i] = 2;
+ }
+
+ TEST_CF_SECRET(&secret_eq, sizeof(secret_eq));
+ TEST_CF_SECRET(src, size + offset);
+ TEST_CF_SECRET(result, size + offset);
+
+ mbedtls_ct_memcpy_if(mbedtls_ct_bool(secret_eq), src + offset, src + offset, src + offset, size);
+
+ TEST_CF_PUBLIC(&secret_eq, sizeof(secret_eq));
+ TEST_CF_PUBLIC(src, size + offset);
+ TEST_CF_PUBLIC(result, size + offset);
+
+ ASSERT_COMPARE(expected, size, src + offset, size);
exit:
mbedtls_free(src);
mbedtls_free(src2);