x86-64 strncat: Properly handle the length parameter [BZ# 24097]

  On x32, the size_t parameter may be passed in the lower 32 bits of a
64-bit register with the non-zero upper 32 bits.  The string/memory
functions written in assembly can only use the lower 32 bits of a
64-bit register as length or must clear the upper 32 bits before using
the full 64-bit register for length.

This pach fixes strncat for x32.  Tested on x86-64 and x32.  On x86-64,
libc.so is the same with and without the fix.
---
 .../x86_64/multiarch/strcat-sse2-unaligned.S  |  4 ++
 sysdeps/x86_64/multiarch/strncat-avx2.S       |  4 ++
 sysdeps/x86_64/multiarch/strncat-evex.S       |  5 ++
 sysdeps/x86_64/x32/Makefile                   |  2 +-
 sysdeps/x86_64/x32/tst-size_t-strncat.c       | 59 +++++++++++++++++++
 5 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 sysdeps/x86_64/x32/tst-size_t-strncat.c
  

On Thu, Dec 1, 2022 at 4:37 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On x32, the size_t parameter may be passed in the lower 32 bits of a
> 64-bit register with the non-zero upper 32 bits.  The string/memory
> functions written in assembly can only use the lower 32 bits of a
> 64-bit register as length or must clear the upper 32 bits before using
> the full 64-bit register for length.
>
> This pach fixes strncat for x32.  Tested on x86-64 and x32.  On x86-64,
> libc.so is the same with and without the fix.
> ---
>  .../x86_64/multiarch/strcat-sse2-unaligned.S  |  4 ++
>  sysdeps/x86_64/multiarch/strncat-avx2.S       |  4 ++
>  sysdeps/x86_64/multiarch/strncat-evex.S       |  5 ++
>  sysdeps/x86_64/x32/Makefile                   |  2 +-
>  sysdeps/x86_64/x32/tst-size_t-strncat.c       | 59 +++++++++++++++++++
>  5 files changed, 73 insertions(+), 1 deletion(-)
>  create mode 100644 sysdeps/x86_64/x32/tst-size_t-strncat.c
>
> diff --git a/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S b/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
> index 9d2ca1d504..b0f9c5fa83 100644
> --- a/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
> +++ b/sysdeps/x86_64/multiarch/strcat-sse2-unaligned.S
> @@ -35,6 +35,10 @@
>  ENTRY (STRCAT)
>         mov     %rdi, %r9
>  # ifdef USE_AS_STRNCAT
> +#  ifdef __ILP32__
> +       /* Clear the upper 32 bits.  */
> +       movl    %edx, %edx
> +#  endif
>         mov     %rdx, %r8
>  # endif
>
> diff --git a/sysdeps/x86_64/multiarch/strncat-avx2.S b/sysdeps/x86_64/multiarch/strncat-avx2.S
> index ffa58bd0de..73baeee473 100644
> --- a/sysdeps/x86_64/multiarch/strncat-avx2.S
> +++ b/sysdeps/x86_64/multiarch/strncat-avx2.S
> @@ -51,6 +51,10 @@
>
>         .section SECTION(.text), "ax", @progbits
>  ENTRY(STRNCAT)
> +# ifdef __ILP32__
> +       /* Clear the upper 32 bits.  */
> +       movl    %edx, %edx
> +# endif
>         /* Filter zero length strings and very long strings.  Zero
>            length strings just return, very long strings are handled by
>            using the non-length variant {wcs|str}cat.  */
> diff --git a/sysdeps/x86_64/multiarch/strncat-evex.S b/sysdeps/x86_64/multiarch/strncat-evex.S
> index bced4e8944..1ef3a22209 100644
> --- a/sysdeps/x86_64/multiarch/strncat-evex.S
> +++ b/sysdeps/x86_64/multiarch/strncat-evex.S
> @@ -79,6 +79,11 @@
>
>         .section SECTION(.text), "ax", @progbits
>  ENTRY(STRNCAT)
> +# ifdef __ILP32__
> +       /* Clear the upper 32 bits.  */
> +       movl    %edx, %edx
> +# endif
> +
>         movq    %rdi, %rax
>
>         /* NB: It's safe to filter out zero-length strings WITHOUT
> diff --git a/sysdeps/x86_64/x32/Makefile b/sysdeps/x86_64/x32/Makefile
> index 31732aa248..a015789a4f 100644
> --- a/sysdeps/x86_64/x32/Makefile
> +++ b/sysdeps/x86_64/x32/Makefile
> @@ -10,7 +10,7 @@ ifeq ($(subdir),string)
>  tests += tst-size_t-memchr tst-size_t-memcmp tst-size_t-memcpy \
>          tst-size_t-memrchr tst-size_t-memset tst-size_t-strncasecmp \
>          tst-size_t-strncmp tst-size_t-strncpy tst-size_t-strnlen \
> -        tst-size_t-memcmp-2
> +        tst-size_t-memcmp-2 tst-size_t-strncat
>  endif
>
>  ifeq ($(subdir),wcsmbs)
> diff --git a/sysdeps/x86_64/x32/tst-size_t-strncat.c b/sysdeps/x86_64/x32/tst-size_t-strncat.c
> new file mode 100644
> index 0000000000..eda93f5af9
> --- /dev/null
> +++ b/sysdeps/x86_64/x32/tst-size_t-strncat.c
> @@ -0,0 +1,59 @@
> +/* Test strncat with size_t in the lower 32 bits of 64-bit register.
> +   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_NAME "strncat"
> +#include "test-size_t.h"
> +
> +IMPL (strncat, 1)
> +
> +typedef char *(*proto_t) (char *, const char*, size_t);
> +
> +static void *
> +__attribute__ ((noinline, noclone))
> +do_strncat (parameter_t a, parameter_t b)
> +{
> +  return CALL (&b, a.p, b.p, a.len);
> +}
> +
> +static int
> +test_main (void)
> +{
> +  test_init ();
> +
> +  parameter_t dest = { { page_size - 1 }, buf1 };
> +  parameter_t src = { { 0 }, buf2 };
> +
> +  int ret = 0;
> +  FOR_EACH_IMPL (impl, 0)
> +    {
> +      src.fn = impl->fn;
> +      buf1[0] = '\0';
> +      do_strncat (dest, src);
> +      int res = strncmp (dest.p, src.p, dest.len);
> +      if (res)
> +       {
> +         error (0, 0, "Wrong result in function %s: %i != 0",
> +                impl->name, res);
> +         ret = 1;
> +       }
> +    }
> +
> +  return ret ? EXIT_FAILURE : EXIT_SUCCESS;
> +}
> +
> +#include <support/test-driver.c>
> --
> 2.38.1
>

LGTM.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>