Re: [PATCH v1 2/2] nptl: Add a testcase for inputs racey to {w}memcmp{eq} BZ #29863

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Mon, Dec 19, 2022 at 11:27 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> Add test that modifies data as {w}memcmp{eq} runs (creating a race
> condition).  Failures from this tests do not inherently mean the
> {w}memcmp{eq} implementation is buggy, but is at the very least
> something we should be aware of.
>
> Success is no SIGSEGV. Failure is a SIGSEGV.
>
> Verified test failed 10/10 times without:
>
> commit b712be52645282c706a5faa038242504feb06db5
> Author: Noah Goldstein <goldstein.w.n@gmail.com>
> Date:   Wed Dec 14 10:52:10 2022 -0800
>
>     x86: Prevent SIGSEGV in memcmp-sse2 when data is concurrently modified [BZ #29863]
>
> And passes with the fix.

NB: Forget tag "Co-authored-by: H.J. Lu <hjl.tools@gmail.com>",
will add before commit or next version if more revisions are needed.
> ---
>  nptl/Makefile            |   7 ++
>  nptl/tst-memcmp-race.c   | 149 +++++++++++++++++++++++++++++++++++++++
>  nptl/tst-memcmpeq-race.c |  19 +++++
>  nptl/tst-wmemcmp-race.c  |  20 ++++++
>  4 files changed, 195 insertions(+)
>  create mode 100644 nptl/tst-memcmp-race.c
>  create mode 100644 nptl/tst-memcmpeq-race.c
>  create mode 100644 nptl/tst-wmemcmp-race.c
>
> diff --git a/nptl/Makefile b/nptl/Makefile
> index fc955cd604..5f56bdc80a 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -285,6 +285,8 @@ tests = \
>         tst-exec4 \
>         tst-exec5 \
>         tst-initializers1 $(addprefix tst-initializers1-,c89 gnu89 c99 gnu99 c11 gnu11) \
> +       tst-memcmp-race \
> +       tst-memcmpeq-race \
>         tst-minstack-cancel \
>         tst-minstack-exit \
>         tst-minstack-throw \
> @@ -348,8 +350,13 @@ tests = \
>         tst-thread_local1 \
>         tst-tsd3 \
>         tst-tsd4 \
> +       tst-wmemcmp-race \
>  # tests
>
> +CFLAGS-tst-memcmp-race.c += -O0
> +CFLAGS-tst-memcmpeq-race.c += -O0
> +CFLAGS-tst-wmemcmp-race.c += -O0
> +
>  tests-nolibpthread = \
>    tst-pthread_exit-nothreads \
>    tst-pthread_exit-nothreads-static \
> diff --git a/nptl/tst-memcmp-race.c b/nptl/tst-memcmp-race.c
> new file mode 100644
> index 0000000000..56e62b2f7b
> --- /dev/null
> +++ b/nptl/tst-memcmp-race.c
> @@ -0,0 +1,149 @@
> +/* Test case for memcmp with race condition.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Verify that there is no segfault when one thread is updating the
> +   memory block of memcmp and the other thread is doing memcmp.
> +
> +   NOTE: This test failing does not automatically mean the
> +   {w}memcmp{eq} is incorrect.  This is testing UB and behavior that
> +   is supported.  That being said, users may expect that the mem*
> +   functions never access out of bounds data (even with data races)
> +   and we should be aware of the cases when we do. */
> +
> +#define TEST_MAIN
> +#define MIN_PAGE_SIZE 4096
> +
> +#ifdef TEST_MEMCMPEQ
> +# define MEMCMP __memcmpeq
> +# define TEST_NAME "__memcmpeq"
> +#elif defined WIDE
> +# define MEMCMP wmemcmp
> +# define TEST_NAME "wmemcmp"
> +#else
> +# define MEMCMP memcmp
> +# define TEST_NAME "memcmp"
> +#endif
> +
> +#ifdef WIDE
> +# define MEMSET wmemset
> +# define CHAR wchar_t
> +#else
> +# define MEMSET memset
> +# define CHAR char
> +#endif
> +
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <string/test-string.h>
> +#include <support/xthread.h>
> +
> +#define NUM_THREADS 2
> +#define LOOP1 10000
> +#define LOOP2 1000000
> +
> +typedef int (*proto_t) (const CHAR *, const CHAR *, size_t);
> +
> +IMPL (MEMCMP, 1)
> +
> +struct arg
> +{
> +  proto_t func;
> +  CHAR *a;
> +  CHAR *b;
> +  size_t len;
> +  size_t wpos;
> +  int todo;
> +};
> +
> +static void *
> +childThread (void *tArgs)
> +{
> +  struct arg *args = (struct arg *) tArgs;
> +  int i;
> +  if (0 == args->todo % 2)
> +    {
> +      for (i = 0; i < LOOP1; i++)
> +       {
> +         volatile int result = args->func (args->a, args->b, args->len);
> +      (void)(result);
> +       }
> +    }
> +  else
> +    {
> +      for (i = 0; i < LOOP2; i++)
> +       args->a[args->wpos] = i & 1;
> +      args->a[args->wpos] = 1;
> +    }
> +  return NULL;
> +}
> +
> +static void
> +do_one_test (proto_t func, size_t len)
> +{
> +  int r;
> +  if (len * sizeof (CHAR) > page_size)
> +    return;
> +  for (r = 0; r < 2; ++r)
> +    {
> +      size_t wpos;
> +      for (wpos = 1; wpos < 128 && wpos <= len; wpos = wpos + wpos + 1)
> +       {
> +         int i;
> +         size_t off;
> +         pthread_t threads[NUM_THREADS];
> +         struct arg a[NUM_THREADS];
> +
> +         off = r ? (page_size - len * sizeof (CHAR)) : 0;
> +         for (i = 0; i < NUM_THREADS; ++i)
> +           {
> +             a[i].func = func;
> +             a[i].a = (CHAR *) (buf1 + off);
> +             a[i].b = (CHAR *) (buf2 + off);
> +             a[i].len = len;
> +             a[i].wpos = len - wpos;
> +             a[i].todo = i;
> +             threads[i] = xpthread_create (NULL, childThread, (void *) &a[i]);
> +           }
> +
> +         for (i = 0; i < NUM_THREADS; ++i)
> +           xpthread_join (threads[i]);
> +       }
> +    }
> +}
> +
> +int
> +test_main (void)
> +{
> +  test_init ();
> +
> +  MEMSET ((CHAR *) buf1, 1, page_size / sizeof (CHAR));
> +  MEMSET ((CHAR *) buf2, 1, page_size / sizeof (CHAR));
> +  for (size_t i = 1; i <= 1024; i += i)
> +    {
> +      FOR_EACH_IMPL (impl, 0)
> +       {
> +         do_one_test ((proto_t) impl->fn, i);
> +         do_one_test ((proto_t) impl->fn, i + 1);
> +         do_one_test ((proto_t) impl->fn, i - 1);
> +       }
> +    }
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/nptl/tst-memcmpeq-race.c b/nptl/tst-memcmpeq-race.c
> new file mode 100644
> index 0000000000..7088928f49
> --- /dev/null
> +++ b/nptl/tst-memcmpeq-race.c
> @@ -0,0 +1,19 @@
> +/* Test case for __memcmpeq with race condition.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +#define TEST_MEMCMPEQ 1
> +#include "tst-memcmp-race.c"
> diff --git a/nptl/tst-wmemcmp-race.c b/nptl/tst-wmemcmp-race.c
> new file mode 100644
> index 0000000000..8278f71842
> --- /dev/null
> +++ b/nptl/tst-wmemcmp-race.c
> @@ -0,0 +1,20 @@
> +/* Test case for wmemcmp with race condition.
> +   Copyright (C) 2022 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +#include <wchar.h>
> +#define WIDE 1
> +#include "tst-memcmp-race.c"
> --
> 2.34.1
>