On Wed, 8 Mar 2023, Marek Polacek wrote:
> 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.
>
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/12?
I think this is a reasonable way to address the regression, so OK.
Thanks,
Richard.
> 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.
> ---
> 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 ++++++++++++++++
> 5 files changed, 82 insertions(+)
> create mode 100644 gcc/testsuite/c-c++-common/ubsan/bounds-17.c
> create mode 100644 gcc/testsuite/c-c++-common/ubsan/bounds-18.c
> create mode 100644 gcc/testsuite/c-c++-common/ubsan/bounds-19.c
> create mode 100644 gcc/testsuite/c-c++-common/ubsan/bounds-20.c
>
> 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\\\]'" } */
>
> base-commit: 2e3dd14dd287ca94b72c36ed28a1ae30887f77ce
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
