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Document and test that memcpy_if may have src == dest

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Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
This commit is contained in:
Dave Rodgman 2023-05-18 13:47:13 +01:00
parent 2c76484005
commit 3108645d67
2 changed files with 29 additions and 3 deletions
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8
library/constant_time_internal.h
View file

@ -417,9 +417,11 @@ void mbedtls_ct_memmove_left(void *start,
*
* \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 @@ void mbedtls_ct_memcpy_if(mbedtls_ct_condition_t condition,
* 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.

24
tests/suites/test_suite_constant_time.function
View file

@ -224,6 +224,7 @@ void mbedtls_ct_memcpy_if(int eq, int size, int offset)
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 @@ void mbedtls_ct_memcpy_if(int eq, int size, int offset)
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 @@ void mbedtls_ct_memcpy_if(int eq, int size, int offset)
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 @@ void mbedtls_ct_memcpy_if(int eq, int size, int offset)
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);