mbedtls_to_psa_error: prefer dispatching on the low-level error
When an Mbed TLS error code combines a low-level error and a
high-level error, the low-level error is usually closer to the root
cause (for example HW_ACCEL_FAILED or ENTROPY_SOURCE_FAILED is more
informative than RSA_PRIVATE_FAILED). So prioritize the low-level code
when converting to a PSA error code, rather than the high-level code
as was (rather arbitrarily) done before.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 73f5a6e..b7c4591 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -135,9 +135,11 @@
psa_status_t mbedtls_to_psa_error( int ret )
{
- /* If there's both a high-level code and low-level code, dispatch on
- * the high-level code. */
- switch( ret < -0x7f ? - ( -ret & 0x7f80 ) : ret )
+ /* Mbed TLS error codes can combine a high-level error code and a
+ * low-level error code. The low-level error usually reflects the
+ * root cause better, so dispatch on that preferably. */
+ int low_level_ret = - ( -ret & 0x007f );
+ switch( low_level_ret != 0 ? low_level_ret : ret )
{
case 0:
return( PSA_SUCCESS );