[kvm-unit-tests] x86: access: avoid undefined behavior

Commit Message

Paolo Bonzini Aug. 9, 2019, 10:57 a.m. UTC

In this test, at->ptep is tested in one argument to ac_test_check
and dereferenced in another.  The compiler notices that and observes
that at->ptep cannot be NULL.  The test is indeed broken and has
been broken for 9+ years: the ac_test_check should not be performed at
all if there is no PTE.

Signed-off-by: Paolo Bonzini <[e-mail]>
---
 x86/access.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Patch

diff --git a/x86/access.c b/x86/access.c
index f0d1879..4ec0b0a 100644
--- a/x86/access.c
+++ b/x86/access.c
@@ -704,8 +704,9 @@  static int ac_test_do_access(ac_test_t *at)
                   "unexpected access");
     ac_test_check(at, &success, fault && e != at->expected_error,
                   "error code %x expected %x", e, at->expected_error);
-    ac_test_check(at, &success, at->ptep && *at->ptep != at->expected_pte,
-                  "pte %x expected %x", *at->ptep, at->expected_pte);
+    if (at->ptep)
+        ac_test_check(at, &success, *at->ptep != at->expected_pte,
+                      "pte %x expected %x", *at->ptep, at->expected_pte);
     ac_test_check(at, &success,
                   !pt_match(*at->pdep, at->expected_pde, at->ignore_pde),
                   "pde %x expected %x", *at->pdep, at->expected_pde);