[ot] hw/opentitan: ot_keymgr: Model KMAC_DONE and KMAC_OUT faults

Though we likely wouldn't expect to see either of these faults in QEMU
when everything is working, modeling these faults helps both more
closely align with the actual HW, and should help debugging the QEMU
model if errors do occur (e.g a KMAC issue could manifest as a
`KMAC_OUT` fault in the `keymgr`, aiding in debugging).

Signed-off-by: Alex Jones <[email protected]>

Author: AlexJones0

hw/opentitan/ot_keymgr.c

@@ -1246,8 +1246,6 @@ static void ot_keymgr_operation_advance(OtKeyMgrState *s, OtKeyMgrStage stage,
     trace_ot_keymgr_advance(s->ot_id, STAGE_NAME(stage), (int)stage,
                             CDI_NAME(cdi), (int)cdi);
 
-    /* @todo: do we need to check for any error states here? */
-
     ot_keymgr_reset_kdf_buffer(s);
 
     size_t expected_kdf_len = 0u;
@@ -1564,13 +1562,38 @@ ot_keymgr_handle_kmac_response(void *opaque, const OtKMACAppRsp *rsp)
         }
     }
 
+    if (!s->op_state.op_req) {
+        /* KMAC response when we weren't expecting one */
+        s->regs[R_FAULT_STATUS] |= R_FAULT_STATUS_KMAC_DONE_MASK;
+        ot_keymgr_update_alerts(s);
+        ot_keymgr_schedule_fsm(s);
+        return;
+    }
+
     if (!rsp->done) {
         /* not the last response from KMAC, send more data */
         ot_keymgr_send_kmac_req(s);
         return;
     }
 
-    g_assert(s->kdf_buf.offset == s->kdf_buf.length);
+    if (s->kdf_buf.offset != s->kdf_buf.length) {
+        /* KMAC interface reports done but we did not send the whole KDF buf */
+        s->regs[R_FAULT_STATUS] |= R_FAULT_STATUS_KMAC_DONE_MASK;
+        ot_keymgr_update_alerts(s);
+        ot_keymgr_schedule_fsm(s);
+        return;
+    }
+
+    /* @todo: check share1 as well when KMAC masking is supported */
+    bool share0_valid = ot_keymgr_valid_data_check(rsp->digest_share0,
+                                                   OT_KMAC_APP_DIGEST_BYTES);
+    if (!share0_valid) {
+        /* KMAC returned all 0s or all 1s*/;
+        s->regs[R_FAULT_STATUS] |= R_FAULT_STATUS_KMAC_OUT_MASK;
+        ot_keymgr_update_alerts(s);
+        ot_keymgr_schedule_fsm(s);
+        return;
+    }
 
     uint32_t ctrl = ot_shadow_reg_peek(&s->control);
     bool op_complete;