[PATCH] asan: Fix up instrumentation of assignments which are both loads and stores [PR105714]

[Jakub Jelinek <jakub@redhat.com>]

Hi!

On the following testcase with -Os asan pass sees:
  <bb 6> [local count: 354334800]:
  # h_21 = PHI <h_15(6), 0(5)>
  *c.3_5 = *d.2_4;
  h_15 = h_21 + 1;
  if (h_15 != 3)
    goto <bb 6>; [75.00%]
  else
    goto <bb 7>; [25.00%]

  <bb 7> [local count: 118111600]:
  *c.3_5 = MEM[(struct a *)&b + 12B];
  _13 = c.3_5->x;
  return _13;
It instruments the
  *c.3_5 = *d.2_4;
assignment by adding
  .ASAN_CHECK (7, c.3_5, 4, 4);
  .ASAN_CHECK (6, d.2_4, 4, 4);
before it (which later lowers to checking the corresponding shadow
memory).  But when considering instrumentation of
  *c.3_5 = MEM[(struct a *)&b + 12B];
it doesn't instrument anything, because it sees that *c.3_5 store is
already instrumented in a dominating block and so there is no need
to instrument *c.3_5 store again (i.e. add another
  .ASAN_CHECK (7, c.3_5, 4, 4);
).  That is true, but misses the fact that we still want to
instrument the MEM[(struct a *)&b + 12B] load.

The following patch fixes that by changing has_stmt_been_instrumented_p
to consider both store and load in the assignment if it does both
(returning true iff both have been instrumented).
That matches how we handle e.g. builtin calls, where we also perform AND
of all the memory locs involved in the call.

I've verified that we still don't add the redundant
  .ASAN_CHECK (7, c.3_5, 4, 4);
call but just add
  _18 = &MEM[(struct a *)&b + 12B];
  .ASAN_CHECK (6, _18, 4, 4);
to instrument the load.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2022-05-25  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/105714
	* asan.cc (has_stmt_been_instrumented_p): For assignments which
	are both stores and loads, return true only if both destination
	and source have been instrumented.

	* gcc.dg/asan/pr105714.c: New test.

--- gcc/asan.cc.jj	2022-05-12 08:27:56.923834018 +0200
+++ gcc/asan.cc	2022-05-24 11:39:28.527258357 +0200
@@ -1285,7 +1285,20 @@ has_stmt_been_instrumented_p (gimple *st
 
       if (get_mem_ref_of_assignment (as_a <gassign *> (stmt), &r,
 				     &r_is_store))
-	return has_mem_ref_been_instrumented (&r);
+	{
+	  if (!has_mem_ref_been_instrumented (&r))
+	    return false;
+	  if (r_is_store && gimple_assign_load_p (stmt))
+	    {
+	      asan_mem_ref src;
+	      asan_mem_ref_init (&src, NULL, 1);
+	      src.start = gimple_assign_rhs1 (stmt);
+	      src.access_size = int_size_in_bytes (TREE_TYPE (src.start));
+	      if (!has_mem_ref_been_instrumented (&src))
+		return false;
+	    }
+	  return true;
+	}
     }
   else if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
     {
--- gcc/testsuite/gcc.dg/asan/pr105714.c.jj	2022-05-24 11:50:26.753570348 +0200
+++ gcc/testsuite/gcc.dg/asan/pr105714.c	2022-05-24 11:51:01.074225766 +0200
@@ -0,0 +1,33 @@
+/* PR sanitizer/105714 */
+/* { dg-do run } */
+/* { dg-skip-if "" { *-*-* } { "*" } { "-Os" } } */
+/* { dg-shouldfail "asan" } */
+
+struct A { int x; };
+struct A b[2];
+struct A *c = b, *d = b;
+int e;
+
+int
+foo ()
+{
+  for (e = 0; e < 1; e++)
+    {
+      int i[1];
+      i;
+    }
+  for (int h = 0; h < 3; h++)
+    *c = *d;
+  *c = *(b + 3);
+  return c->x;
+}
+
+int
+main ()
+{
+  foo ();
+  return 0;
+}
+
+/* { dg-output "ERROR: AddressSanitizer: global-buffer-overflow on address.*(\n|\r\n|\r)" } */
+/* { dg-output "READ of size.*" } */

	Jakub