[ubsan PATCH] -fsanitize=null fails to sanitize &s->i (PR sanitizer/80797)

[Marek Polacek]

We are failing to detect accessing a null pointer in &s->i because
v_3 = &s_2->i;
is not gimple_assign_load_p:  
1997           if (flag_sanitize & (SANITIZE_NULL | SANITIZE_ALIGNMENT))
1998             {
1999               if (gimple_store_p (stmt))
2000                 instrument_null (gsi, true);
2001               if (gimple_assign_load_p (stmt))
2002                 instrument_null (gsi, false);
2003             }

So I think we can use gimple_assign_single_p instead of gimple_assign_load_p
and then strip the ADDR_EXPR in instrument_null before getting its base
address.  (I've seen stripping ADDR_EXPR before get_base_address elsewhere in
the codebase, too.)

Bootstrapped-ubsan/regtested on x86_64-linux, ok for trunk?

2017-05-17  Marek Polacek  <pola...@redhat.com>

        PR sanitizer/80797
        * ubsan.c (instrument_null): Unwrap ADDR_EXPRs.
        (pass_ubsan::execute): Call gimple_assign_single_p instead of
        gimple_assign_load_p.

        * c-c++-common/ubsan/null-12.c: New test.

diff --git gcc/testsuite/c-c++-common/ubsan/null-12.c 
gcc/testsuite/c-c++-common/ubsan/null-12.c
index e69de29..3478dc1 100644
--- gcc/testsuite/c-c++-common/ubsan/null-12.c
+++ gcc/testsuite/c-c++-common/ubsan/null-12.c
@@ -0,0 +1,42 @@
+/* PR sanitizer/80797 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=undefined" } */
+
+struct S
+{
+  int i;
+};
+
+struct R
+{
+  struct T {
+    int i;
+  } *t;
+} r;
+
+int
+main ()
+{
+  struct S *s = 0;
+  struct S *s2[1] = { };
+
+  int *v1 = &s->i;
+  int *v2 = &(*s).i;
+  int *v3 = &s2[0]->i;
+  int *v4 = &s->i + 1;
+  int *v5 = &r.t->i;
+
+  asm ("" : : "r" (&v1) : "memory");
+  asm ("" : : "r" (&v2) : "memory");
+  asm ("" : : "r" (&v3) : "memory");
+  asm ("" : : "r" (&v4) : "memory");
+  asm ("" : : "r" (&v5) : "memory");
+
+  return 0;
+}
+
+/* { dg-output "member access within null pointer of type 'struct 
S'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*member access within null pointer of type 'struct 
S'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*member access within null pointer of type 'struct 
S'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*member access within null pointer of type 'struct 
S'\[^\n\r]*(\n|\r\n|\r)" } */
+/* { dg-output "\[^\n\r]*member access within null pointer of type 'struct T'" 
} */
diff --git gcc/ubsan.c gcc/ubsan.c
index 4159cc5..a4808d2 100644
--- gcc/ubsan.c
+++ gcc/ubsan.c
@@ -1208,6 +1208,9 @@ instrument_null (gimple_stmt_iterator gsi, bool is_lhs)
 {
   gimple *stmt = gsi_stmt (gsi);
   tree t = is_lhs ? gimple_get_lhs (stmt) : gimple_assign_rhs1 (stmt);
+  /* Handle also e.g. &s->i.  */
+  if (TREE_CODE (t) == ADDR_EXPR)
+    t = TREE_OPERAND (t, 0);
   tree base = get_base_address (t);
   const enum tree_code code = TREE_CODE (base);
   if (code == MEM_REF
@@ -1998,7 +2001,7 @@ pass_ubsan::execute (function *fun)
            {
              if (gimple_store_p (stmt))
                instrument_null (gsi, true);
-             if (gimple_assign_load_p (stmt))
+             if (gimple_assign_single_p (stmt))
                instrument_null (gsi, false);
            }
 

        Marek