[Bug sanitizer/108060] [10/11/12/13 Regression] UBsan missed an out-of-bound bug at -O0 since r7-1900-g8a1b7b7fd75a3847

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108060

--- Comment #8 from CVS Commits  ---
The trunk branch has been updated by Marek Polacek :

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

commit r13-6593-g4d0baeae315ebe7d0ec7682ea3e7c0516027c2b8
Author: Marek Polacek 
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 , 8);, SAVE_EXPR ;] = 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 , 8);, SAVE_EXPR ;] | 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

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.

[Bug sanitizer/108060] [10/11/12/13 Regression] UBsan missed an out-of-bound bug at -O0 since r7-1900-g8a1b7b7fd75a3847

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108060

Andrew Pinski  changed:

   What|Removed |Added

Summary|UBsan missed an |[10/11/12/13 Regression]
   |out-of-bound bug at -O0 |UBsan missed an
   |since   |out-of-bound bug at -O0
   |r7-1900-g8a1b7b7fd75a3847   |since
   ||r7-1900-g8a1b7b7fd75a3847
   Target Milestone|--- |10.5