[ownership] Fix key algo comparison hardening

We used XOR for the comparison hardening, but didn't realize that might flip
false to true. Luckily, the allowed values checked before calling the function
makes the flip impossible.

This commit changes to normal comparison to eliminating the corner case.

Change-Id: I7e4c7cdfd3d53a70852ecf97939fdce56a7b0cd8
Signed-off-by: Yi-Hsuan Deng <[email protected]>

Author: sasdf

sw/device/silicon_creator/lib/ownership/owner_block.c

@@ -44,15 +44,15 @@ enum {
 };
 
 hardened_bool_t owner_block_owner_key_equal(void) {
-  hardened_bool_t result =
-      hardened_memeq(owner_page[0].owner_key.raw, owner_page[1].owner_key.raw,
-                     ARRAYSIZE(owner_page[0].owner_key.raw));
-  result ^= owner_page[0].ownership_key_alg;
-  result ^= owner_page[1].ownership_key_alg;
-  if (launder32(result) != kHardenedBoolTrue) {
+  if (launder32(owner_page[0].ownership_key_alg) !=
+      launder32(owner_page[1].ownership_key_alg)) {
     return kHardenedBoolFalse;
   }
-  return result;
+  HARDENED_CHECK_EQ(owner_page[0].ownership_key_alg,
+                    owner_page[1].ownership_key_alg);
+  return hardened_memeq(owner_page[0].owner_key.raw,
+                        owner_page[1].owner_key.raw,
+                        ARRAYSIZE(owner_page[0].owner_key.raw));
 }
 
 hardened_bool_t owner_block_newversion_mode(void) {