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From: Paolo Bonzini <pbonzini@redhat.com>
To: kvm@vger.kernel.org
Subject: [PATCH kvm-unit-tests] x86: access: avoid undefined behavior
Date: Fri,  9 Aug 2019 12:57:14 +0200	[thread overview]
Message-ID: <20190809105714.9450-1-pbonzini@redhat.com> (raw)

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 <pbonzini@redhat.com>
---
 x86/access.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

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);
-- 
2.21.0


                 reply	other threads:[~2019-08-09 10:57 UTC|newest]

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