[gcc r13-6593] ubsan: missed -fsanitize=bounds for compound ops [PR108060]

[gcc r13-6593] ubsan: missed -fsanitize=bounds for compound ops [PR108060]

[Marek Polacek]

https://gcc.gnu.org/g:4d0baeae315ebe7d0ec7682ea3e7c0516027c2b8

commit r13-6593-g4d0baeae315ebe7d0ec7682ea3e7c0516027c2b8
Author: Marek Polacek <polacek@redhat.com>
Date:   Wed Mar 8 09:15:07 2023 -0500

    ubsan: missed -fsanitize=bounds for compound ops [PR108060]
    
    In this PR we are dealing with a missing .UBSAN_BOUNDS, so the
    out-of-bounds access in the test makes the program crash before
    a UBSan diagnostic was emitted.  In C and C++, c_genericize gets
    
      a[b] = a[b] | c;
    
    but in C, both a[b] are one identical shared tree (not in C++ because
    cp_fold/ARRAY_REF created two same but not identical trees).  Since
    ubsan_walk_array_refs_r keeps a pset, in C we produce
    
      a[.UBSAN_BOUNDS (0B, SAVE_EXPR <b>, 8);, SAVE_EXPR <b>;] = a[b] | c;
    
    because the LHS is walked before the RHS.
    
    Since r7-1900, we gimplify the RHS before the LHS.  So the statement above
    gets gimplified into
    
        _1 = a[b];
        c.0_2 = c;
        b.1 = b;
        .UBSAN_BOUNDS (0B, b.1, 8);
    
    With this patch we produce:
    
      a[b] = a[.UBSAN_BOUNDS (0B, SAVE_EXPR <b>, 8);, SAVE_EXPR <b>;] | c;
    
    which gets gimplified into:
    
        b.0 = b;
        .UBSAN_BOUNDS (0B, b.0, 8);
        _1 = a[b.0];
    
    therefore we emit a runtime error before making the bad array access.
    
    I think it's OK that only the RHS gets a .UBSAN_BOUNDS, as in few lines
    above: the instrumented array access dominates the array access on the
    LHS, and I've verified that
    
      b = 0;
      a[b] = (a[b], b = -32768, a[0] | c);
    
    works as expected: the inner a[b] is OK but we do emit an error for the
    a[b] on the LHS.
    
    For GCC 14, we could apply
    <https://gcc.gnu.org/pipermail/gcc-patches/2023-March/613687.html>
    since the copy_node doesn't seem to be needed.
    
            PR sanitizer/108060
            PR sanitizer/109050
    
    gcc/c-family/ChangeLog:
    
            * c-gimplify.cc (ubsan_walk_array_refs_r): For a MODIFY_EXPR, instrument
            the RHS before the LHS.
    
    gcc/testsuite/ChangeLog:
    
            * c-c++-common/ubsan/bounds-17.c: New test.
            * c-c++-common/ubsan/bounds-18.c: New test.
            * c-c++-common/ubsan/bounds-19.c: New test.
            * c-c++-common/ubsan/bounds-20.c: New test.
            * c-c++-common/ubsan/bounds-21.c: New test.

Diff:
---
 gcc/c-family/c-gimplify.cc                   | 12 ++++++++++++
 gcc/testsuite/c-c++-common/ubsan/bounds-17.c | 17 +++++++++++++++++
 gcc/testsuite/c-c++-common/ubsan/bounds-18.c | 17 +++++++++++++++++
 gcc/testsuite/c-c++-common/ubsan/bounds-19.c | 20 ++++++++++++++++++++
 gcc/testsuite/c-c++-common/ubsan/bounds-20.c | 16 ++++++++++++++++
 gcc/testsuite/c-c++-common/ubsan/bounds-21.c | 18 ++++++++++++++++++
 6 files changed, 100 insertions(+)

diff --git a/gcc/c-family/c-gimplify.cc b/gcc/c-family/c-gimplify.cc
index 74b276b2b26..ef5c7d919fc 100644
--- a/gcc/c-family/c-gimplify.cc
+++ b/gcc/c-family/c-gimplify.cc
@@ -106,6 +106,18 @@ ubsan_walk_array_refs_r (tree *tp, int *walk_subtrees, void *data)
     }
   else if (TREE_CODE (*tp) == ARRAY_REF)
     ubsan_maybe_instrument_array_ref (tp, false);
+  else if (TREE_CODE (*tp) == MODIFY_EXPR)
+    {
+      /* Since r7-1900, we gimplify RHS before LHS.  Consider
+	   a[b] |= c;
+	 wherein we can have a single shared tree a[b] in both LHS and RHS.
+	 If we only instrument the LHS and the access is invalid, the program
+	 could crash before emitting a UBSan error.  So instrument the RHS
+	 first.  */
+      *walk_subtrees = 0;
+      walk_tree (&TREE_OPERAND (*tp, 1), ubsan_walk_array_refs_r, pset, pset);
+      walk_tree (&TREE_OPERAND (*tp, 0), ubsan_walk_array_refs_r, pset, pset);
+    }
   return NULL_TREE;
 }
 
diff --git a/gcc/testsuite/c-c++-common/ubsan/bounds-17.c b/gcc/testsuite/c-c++-common/ubsan/bounds-17.c
new file mode 100644
index 00000000000..b727e3235b8
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/ubsan/bounds-17.c
@@ -0,0 +1,17 @@
+/* PR sanitizer/108060 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=bounds" } */
+/* { dg-skip-if "" { *-*-* } "-flto" } */
+/* { dg-shouldfail "ubsan" } */
+
+int a[8];
+int c;
+
+int
+main ()
+{
+  int b = -32768;
+  a[b] |= c;
+}
+
+/* { dg-output "index -32768 out of bounds for type 'int \\\[8\\\]'" } */
diff --git a/gcc/testsuite/c-c++-common/ubsan/bounds-18.c b/gcc/testsuite/c-c++-common/ubsan/bounds-18.c
new file mode 100644
index 00000000000..556abc0e1c0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/ubsan/bounds-18.c
@@ -0,0 +1,17 @@
+/* PR sanitizer/108060 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=bounds" } */
+/* { dg-skip-if "" { *-*-* } "-flto" } */
+/* { dg-shouldfail "ubsan" } */
+
+int a[8];
+int c;
+
+int
+main ()
+{
+  int b = -32768;
+  a[b] = a[b] | c;
+}
+
+/* { dg-output "index -32768 out of bounds for type 'int \\\[8\\\]'" } */
diff --git a/gcc/testsuite/c-c++-common/ubsan/bounds-19.c b/gcc/testsuite/c-c++-common/ubsan/bounds-19.c
new file mode 100644
index 00000000000..54217ae399f
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/ubsan/bounds-19.c
@@ -0,0 +1,20 @@
+/* PR sanitizer/108060 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=bounds" } */
+/* { dg-skip-if "" { *-*-* } "-flto" } */
+/* { dg-shouldfail "ubsan" } */
+
+int a[8];
+int a2[18];
+int c;
+
+int
+main ()
+{
+  int b = 0;
+  a[0] = (a2[b], b = -32768, a[0] | c);
+  b = 0;
+  a[b] = (a[b], b = -32768, a[0] | c);
+}
+
+/* { dg-output "index -32768 out of bounds for type 'int \\\[8\\\]'" } */
diff --git a/gcc/testsuite/c-c++-common/ubsan/bounds-20.c b/gcc/testsuite/c-c++-common/ubsan/bounds-20.c
new file mode 100644
index 00000000000..a78c67129e0
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/ubsan/bounds-20.c
@@ -0,0 +1,16 @@
+/* PR sanitizer/109050 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=bounds -fno-sanitize-recover=all" } */
+/* { dg-shouldfail "ubsan" } */
+
+long a;
+int b;
+int
+main ()
+{
+  int c[4] = {0, 1, 2, 3};
+  a = 0;
+  c[a - 9806816] |= b;
+}
+
+/* { dg-output "index -9806816 out of bounds for type 'int \\\[4\\\]'" } */
diff --git a/gcc/testsuite/c-c++-common/ubsan/bounds-21.c b/gcc/testsuite/c-c++-common/ubsan/bounds-21.c
new file mode 100644
index 00000000000..b9d9308849f
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/ubsan/bounds-21.c
@@ -0,0 +1,18 @@
+/* PR sanitizer/109050 */
+/* { dg-do run } */
+/* { dg-options "-fsanitize=bounds -fno-sanitize-recover=all" } */
+
+int i;
+int foo (void) { return ++i; }
+
+int
+main ()
+{
+  char a[10] = { };
+  a[foo ()] = a[foo()] | 'a';
+  if (i != 2)
+    __builtin_abort ();
+  a[foo()] |= 'a';
+  if (i != 3)
+    __builtin_abort ();
+}