commit 9d6a535ba113ebf839f551c1bdaff7d3df50df68
author Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Mon Nov 25 13:06:05 2019 +0100
committer Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com> Tue Nov 26 12:54:06 2019 +0100
tree 17625fedd962dcbf8a0a81d705e0cc0e597fafed
parent 4d6186beb0bca06096be6424daa2c618fb787c30

Return and propagate UECC_FAULT_DETECTED

This commit first changes the return convention of EccPoint_mult_safer() so
that it properly reports when faults are detected. Then all functions that
call it need to be changed to (1) follow the same return convention and (2)
properly propagate UECC_FAULT_DETECTED when it occurs.

Here's the reverse call graph from EccPoint_mult_safer() to the rest of the
library (where return values are translated to the MBEDTLS_ERR_ space) and test
functions (where expected return values are asserted explicitly).

EccPoint_mult_safer()
    EccPoint_compute_public_key()
        uECC_compute_public_key()
            pkparse.c
            tests/suites/test_suite_pkparse.function
        uECC_make_key_with_d()
        uECC_make_key()
            ssl_cli.c
            ssl_srv.c
            tests/suites/test_suite_pk.function
            tests/suites/test_suite_tinycrypt.function
    uECC_shared_secret()
        ssl_tls.c
        tests/suites/test_suite_tinycrypt.function
    uECC_sign_with_k()
        uECC_sign()
            pk.c
            tests/suites/test_suite_tinycrypt.function

Note: in uECC_sign_with_k() a test for uECC_vli_isZero(p) is suppressed
because it is redundant with a more thorough test (point validity) done at the
end of EccPoint_mult_safer(). This redundancy was introduced in a previous
commit but not noticed earlier.

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 2fc569c..c12af96 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1973,14 +1973,13 @@
         mbedtls_ssl_suite_get_key_exchange( ciphersuite_info )
         == MBEDTLS_KEY_EXCHANGE_ECDH_ECDSA )
     {
-        ((void) ret);
-
-        if( !uECC_shared_secret( ssl->handshake->ecdh_peerkey,
-                                 ssl->handshake->ecdh_privkey,
-                                 ssl->handshake->premaster ) )
-        {
+        ret = uECC_shared_secret( ssl->handshake->ecdh_peerkey,
+                                  ssl->handshake->ecdh_privkey,
+                                  ssl->handshake->premaster );
+        if( ret == UECC_FAULT_DETECTED )
+            return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
+        if( ret != UECC_SUCCESS )
             return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
-        }
 
         ssl->handshake->pmslen = NUM_ECC_BYTES;
     }
@@ -2168,14 +2167,13 @@
         size_t zlen;
 
 #if defined(MBEDTLS_USE_TINYCRYPT)
-        ((void) ret);
-
-        if( !uECC_shared_secret( ssl->handshake->ecdh_peerkey,
-                                 ssl->handshake->ecdh_privkey,
-                                 p + 2 ) )
-        {
+        ret = uECC_shared_secret( ssl->handshake->ecdh_peerkey,
+                                  ssl->handshake->ecdh_privkey,
+                                  p + 2 );
+        if( ret == UECC_FAULT_DETECTED )
+            return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
+        if( ret != UECC_SUCCESS )
             return( MBEDTLS_ERR_SSL_HW_ACCEL_FAILED );
-        }
 
         zlen = NUM_ECC_BYTES;
 #else /* MBEDTLS_USE_TINYCRYPT */