diff mbox series

[v1] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]

Message ID 20220215162829.282223-1-goldstein.w.n@gmail.com
State Superseded
Headers
Series [v1] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895] |

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit fail Patch caused testsuite regressions

Commit Message

Noah Goldstein Feb. 15, 2022, 4:28 p.m. UTC 
  Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
are near the start of a page. To avoid having the result contimated by
these comparisons the `strcmp` variants would mask off these
comparisons. This was missing in the `strncmp` variants causing
the bug. This commit adds the masking to `strncmp` so that out of
range comparisons don't affect the result.

test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
well a full xcheck on x86_64 linux.
---
 string/test-strncmp.c                  | 24 ++++++++++++++++++++++++
 sysdeps/x86_64/multiarch/strcmp-avx2.S |  1 +
 sysdeps/x86_64/multiarch/strcmp-evex.S |  1 +
 3 files changed, 26 insertions(+)

Comments

H.J. Lu Feb. 15, 2022, 4:32 p.m. UTC | #1 
On Tue, Feb 15, 2022 at 8:28 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
> are near the start of a page. To avoid having the result contimated by
> these comparisons the `strcmp` variants would mask off these
> comparisons. This was missing in the `strncmp` variants causing
> the bug. This commit adds the masking to `strncmp` so that out of
> range comparisons don't affect the result.
>
> test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
> well a full xcheck on x86_64 linux.
> ---
>  string/test-strncmp.c                  | 24 ++++++++++++++++++++++++
>  sysdeps/x86_64/multiarch/strcmp-avx2.S |  1 +
>  sysdeps/x86_64/multiarch/strcmp-evex.S |  1 +
>  3 files changed, 26 insertions(+)
>
> diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> index 831cb77893..501055de0c 100644
> --- a/string/test-strncmp.c
> +++ b/string/test-strncmp.c
> @@ -423,6 +423,29 @@ check3 (void)
>         }
>  }
>
> +

Remove the extra blank line.

> +static void
> +check4 (void)
> +{
> +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
> +     the end of the page. 2) For there to be no mismatch/null byte before the
> +     first page cross. 3) For length (`n`) to be large enough for one string to
> +     cross the page. And 4) for there to be either mismatch/null bytes before
> +     the start of the strings.  */
> +
> +  size_t size = 10;
> +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
> +  int exp_result;
> +
> +  STRCPY (s1, L ("tst-tlsmod%"));
> +  STRCPY (s2, L ("tst-tls-manydynamic73mod"));
> +  exp_result = SIMPLE_STRNCMP (s1, s2, size);
> +  FOR_EACH_IMPL (impl, 0)
> +  check_result (impl, s1, s2, size, exp_result);
> +}
> +
> +

Remove the extra blank line.

>  static void
>  check_overflow (void)
>  {
> @@ -546,6 +569,7 @@ test_main (void)
>    check1 ();
>    check2 ();
>    check3 ();
> +  check4 ();
>
>    printf ("%23s", "");
>    FOR_EACH_IMPL (impl, 0)
> diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> index 99e5349be8..07a5a2c889 100644
> --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
> +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> @@ -661,6 +661,7 @@ L(ret8):
>  # ifdef USE_AS_STRNCMP
>         .p2align 4,, 10
>  L(return_page_cross_end_check):
> +       andl    %r10d, %ecx
>         tzcntl  %ecx, %ecx
>         leal    -VEC_SIZE(%rax, %rcx), %ecx
>         cmpl    %ecx, %edx
> diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
> index 6f42e3155a..56d8c118e4 100644
> --- a/sysdeps/x86_64/multiarch/strcmp-evex.S
> +++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
> @@ -689,6 +689,7 @@ L(ret8):
>  # ifdef USE_AS_STRNCMP
>         .p2align 4,, 10
>  L(return_page_cross_end_check):
> +       andl    %r10d, %ecx
>         tzcntl  %ecx, %ecx
>         leal    -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
>  #  ifdef USE_AS_WCSCMP
> --
> 2.25.1
>

OK for master and 2.35 backport with the extra blank line removal.

Thanks.
Noah Goldstein Feb. 15, 2022, 4:42 p.m. UTC | #2 
On Tue, Feb 15, 2022 at 10:32 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Tue, Feb 15, 2022 at 8:28 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
> > are near the start of a page. To avoid having the result contimated by
> > these comparisons the `strcmp` variants would mask off these
> > comparisons. This was missing in the `strncmp` variants causing
> > the bug. This commit adds the masking to `strncmp` so that out of
> > range comparisons don't affect the result.
> >
> > test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
> > well a full xcheck on x86_64 linux.
> > ---
> >  string/test-strncmp.c                  | 24 ++++++++++++++++++++++++
> >  sysdeps/x86_64/multiarch/strcmp-avx2.S |  1 +
> >  sysdeps/x86_64/multiarch/strcmp-evex.S |  1 +
> >  3 files changed, 26 insertions(+)
> >
> > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> > index 831cb77893..501055de0c 100644
> > --- a/string/test-strncmp.c
> > +++ b/string/test-strncmp.c
> > @@ -423,6 +423,29 @@ check3 (void)
> >         }
> >  }
> >
> > +
>
> Remove the extra blank line.

Done in V2.
>
> > +static void
> > +check4 (void)
> > +{
> > +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
> > +     the end of the page. 2) For there to be no mismatch/null byte before the
> > +     first page cross. 3) For length (`n`) to be large enough for one string to
> > +     cross the page. And 4) for there to be either mismatch/null bytes before
> > +     the start of the strings.  */
> > +
> > +  size_t size = 10;
> > +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> > +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
> > +  int exp_result;
> > +
> > +  STRCPY (s1, L ("tst-tlsmod%"));
> > +  STRCPY (s2, L ("tst-tls-manydynamic73mod"));
> > +  exp_result = SIMPLE_STRNCMP (s1, s2, size);
> > +  FOR_EACH_IMPL (impl, 0)
> > +  check_result (impl, s1, s2, size, exp_result);
> > +}
> > +
> > +
>
> Remove the extra blank line.

Done in V2.
>
> >  static void
> >  check_overflow (void)
> >  {
> > @@ -546,6 +569,7 @@ test_main (void)
> >    check1 ();
> >    check2 ();
> >    check3 ();
> > +  check4 ();
> >
> >    printf ("%23s", "");
> >    FOR_EACH_IMPL (impl, 0)
> > diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > index 99e5349be8..07a5a2c889 100644
> > --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > @@ -661,6 +661,7 @@ L(ret8):
> >  # ifdef USE_AS_STRNCMP
> >         .p2align 4,, 10
> >  L(return_page_cross_end_check):
> > +       andl    %r10d, %ecx
> >         tzcntl  %ecx, %ecx
> >         leal    -VEC_SIZE(%rax, %rcx), %ecx
> >         cmpl    %ecx, %edx
> > diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
> > index 6f42e3155a..56d8c118e4 100644
> > --- a/sysdeps/x86_64/multiarch/strcmp-evex.S
> > +++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
> > @@ -689,6 +689,7 @@ L(ret8):
> >  # ifdef USE_AS_STRNCMP
> >         .p2align 4,, 10
> >  L(return_page_cross_end_check):
> > +       andl    %r10d, %ecx
> >         tzcntl  %ecx, %ecx
> >         leal    -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
> >  #  ifdef USE_AS_WCSCMP
> > --
> > 2.25.1
> >
>
> OK for master and 2.35 backport with the extra blank line removal.

Bug isn't present in 2.35. We had the foresight to wait until 2.36 to
push this.
>
> Thanks.
>
> --
> H.J.
H.J. Lu Feb. 15, 2022, 4:44 p.m. UTC | #3 
On Tue, Feb 15, 2022 at 8:43 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
>
> On Tue, Feb 15, 2022 at 10:32 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Tue, Feb 15, 2022 at 8:28 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > >
> > > Logic can read before the start of `s1` / `s2` if both `s1` and `s2`
> > > are near the start of a page. To avoid having the result contimated by
> > > these comparisons the `strcmp` variants would mask off these
> > > comparisons. This was missing in the `strncmp` variants causing
> > > the bug. This commit adds the masking to `strncmp` so that out of
> > > range comparisons don't affect the result.
> > >
> > > test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass as
> > > well a full xcheck on x86_64 linux.
> > > ---
> > >  string/test-strncmp.c                  | 24 ++++++++++++++++++++++++
> > >  sysdeps/x86_64/multiarch/strcmp-avx2.S |  1 +
> > >  sysdeps/x86_64/multiarch/strcmp-evex.S |  1 +
> > >  3 files changed, 26 insertions(+)
> > >
> > > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> > > index 831cb77893..501055de0c 100644
> > > --- a/string/test-strncmp.c
> > > +++ b/string/test-strncmp.c
> > > @@ -423,6 +423,29 @@ check3 (void)
> > >         }
> > >  }
> > >
> > > +
> >
> > Remove the extra blank line.
>
> Done in V2.
> >
> > > +static void
> > > +check4 (void)
> > > +{
> > > +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
> > > +     the end of the page. 2) For there to be no mismatch/null byte before the
> > > +     first page cross. 3) For length (`n`) to be large enough for one string to
> > > +     cross the page. And 4) for there to be either mismatch/null bytes before
> > > +     the start of the strings.  */
> > > +
> > > +  size_t size = 10;
> > > +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> > > +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
> > > +  int exp_result;
> > > +
> > > +  STRCPY (s1, L ("tst-tlsmod%"));
> > > +  STRCPY (s2, L ("tst-tls-manydynamic73mod"));
> > > +  exp_result = SIMPLE_STRNCMP (s1, s2, size);
> > > +  FOR_EACH_IMPL (impl, 0)
> > > +  check_result (impl, s1, s2, size, exp_result);
> > > +}
> > > +
> > > +
> >
> > Remove the extra blank line.
>
> Done in V2.
> >
> > >  static void
> > >  check_overflow (void)
> > >  {
> > > @@ -546,6 +569,7 @@ test_main (void)
> > >    check1 ();
> > >    check2 ();
> > >    check3 ();
> > > +  check4 ();
> > >
> > >    printf ("%23s", "");
> > >    FOR_EACH_IMPL (impl, 0)
> > > diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > > index 99e5349be8..07a5a2c889 100644
> > > --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > > +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > > @@ -661,6 +661,7 @@ L(ret8):
> > >  # ifdef USE_AS_STRNCMP
> > >         .p2align 4,, 10
> > >  L(return_page_cross_end_check):
> > > +       andl    %r10d, %ecx
> > >         tzcntl  %ecx, %ecx
> > >         leal    -VEC_SIZE(%rax, %rcx), %ecx
> > >         cmpl    %ecx, %edx
> > > diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
> > > index 6f42e3155a..56d8c118e4 100644
> > > --- a/sysdeps/x86_64/multiarch/strcmp-evex.S
> > > +++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
> > > @@ -689,6 +689,7 @@ L(ret8):
> > >  # ifdef USE_AS_STRNCMP
> > >         .p2align 4,, 10
> > >  L(return_page_cross_end_check):
> > > +       andl    %r10d, %ecx
> > >         tzcntl  %ecx, %ecx
> > >         leal    -VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
> > >  #  ifdef USE_AS_WCSCMP
> > > --
> > > 2.25.1
> > >
> >
> > OK for master and 2.35 backport with the extra blank line removal.
>
> Bug isn't present in 2.35. We had the foresight to wait until 2.36 to
> push this.

Glad to hear it :-).
Andreas Schwab Feb. 15, 2022, 4:48 p.m. UTC | #4 
On Feb 15 2022, Noah Goldstein via Libc-alpha wrote:

> diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> index 831cb77893..501055de0c 100644
> --- a/string/test-strncmp.c
> +++ b/string/test-strncmp.c
> @@ -423,6 +423,29 @@ check3 (void)
>  	}
>  }
>  
> +
> +static void
> +check4 (void)
> +{
> +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
> +     the end of the page. 2) For there to be no mismatch/null byte before the
> +     first page cross. 3) For length (`n`) to be large enough for one string to
> +     cross the page. And 4) for there to be either mismatch/null bytes before
> +     the start of the strings.  */
> +
> +  size_t size = 10;
> +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));

s/&/-/
Noah Goldstein Feb. 15, 2022, 4:49 p.m. UTC | #5 
On Tue, Feb 15, 2022 at 10:48 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>
> On Feb 15 2022, Noah Goldstein via Libc-alpha wrote:
>
> > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> > index 831cb77893..501055de0c 100644
> > --- a/string/test-strncmp.c
> > +++ b/string/test-strncmp.c
> > @@ -423,6 +423,29 @@ check3 (void)
> >       }
> >  }
> >
> > +
> > +static void
> > +check4 (void)
> > +{
> > +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
> > +     the end of the page. 2) For there to be no mismatch/null byte before the
> > +     first page cross. 3) For length (`n`) to be large enough for one string to
> > +     cross the page. And 4) for there to be either mismatch/null bytes before
> > +     the start of the strings.  */
> > +
> > +  size_t size = 10;
> > +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> > +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
>
> s/&/-/
?
>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
Andreas Schwab Feb. 15, 2022, 5:04 p.m. UTC | #6 
On Feb 15 2022, Noah Goldstein wrote:

> On Tue, Feb 15, 2022 at 10:48 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>>
>> On Feb 15 2022, Noah Goldstein via Libc-alpha wrote:
>>
>> > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
>> > index 831cb77893..501055de0c 100644
>> > --- a/string/test-strncmp.c
>> > +++ b/string/test-strncmp.c
>> > @@ -423,6 +423,29 @@ check3 (void)
>> >       }
>> >  }
>> >
>> > +
>> > +static void
>> > +check4 (void)
>> > +{
>> > +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
>> > +     the end of the page. 2) For there to be no mismatch/null byte before the
>> > +     first page cross. 3) For length (`n`) to be large enough for one string to
>> > +     cross the page. And 4) for there to be either mismatch/null bytes before
>> > +     the start of the strings.  */
>> > +
>> > +  size_t size = 10;
>> > +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
>> > +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
>>
>> s/&/-/
> ?

(0x1000 & 0xffa) == 0
Noah Goldstein Feb. 15, 2022, 5:24 p.m. UTC | #7 
On Tue, Feb 15, 2022 at 11:04 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
>
> On Feb 15 2022, Noah Goldstein wrote:
>
> > On Tue, Feb 15, 2022 at 10:48 AM Andreas Schwab <schwab@linux-m68k.org> wrote:
> >>
> >> On Feb 15 2022, Noah Goldstein via Libc-alpha wrote:
> >>
> >> > diff --git a/string/test-strncmp.c b/string/test-strncmp.c
> >> > index 831cb77893..501055de0c 100644
> >> > --- a/string/test-strncmp.c
> >> > +++ b/string/test-strncmp.c
> >> > @@ -423,6 +423,29 @@ check3 (void)
> >> >       }
> >> >  }
> >> >
> >> > +
> >> > +static void
> >> > +check4 (void)
> >> > +{
> >> > +  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
> >> > +     the end of the page. 2) For there to be no mismatch/null byte before the
> >> > +     first page cross. 3) For length (`n`) to be large enough for one string to
> >> > +     cross the page. And 4) for there to be either mismatch/null bytes before
> >> > +     the start of the strings.  */
> >> > +
> >> > +  size_t size = 10;
> >> > +  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
> >> > +  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
> >>
> >> s/&/-/
> > ?
>
> (0x1000 & 0xffa) == 0

:/

Fixed in V3.
>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
> "And now for something completely different."
diff mbox series

Patch

diff --git a/string/test-strncmp.c b/string/test-strncmp.c
index 831cb77893..501055de0c 100644
--- a/string/test-strncmp.c
+++ b/string/test-strncmp.c
@@ -423,6 +423,29 @@  check3 (void)
 	}
 }
 
+
+static void
+check4 (void)
+{
+  /* To trigger bug 28895; We need 1) both s1 and s2 to be within 32 bytes of
+     the end of the page. 2) For there to be no mismatch/null byte before the
+     first page cross. 3) For length (`n`) to be large enough for one string to
+     cross the page. And 4) for there to be either mismatch/null bytes before
+     the start of the strings.  */
+
+  size_t size = 10;
+  CHAR *s1 = (CHAR *)(buf1 + (getpagesize () & 0xffa) / sizeof (CHAR));
+  CHAR *s2 = (CHAR *)(buf2 + (getpagesize () & 0xfed) / sizeof (CHAR));
+  int exp_result;
+
+  STRCPY (s1, L ("tst-tlsmod%"));
+  STRCPY (s2, L ("tst-tls-manydynamic73mod"));
+  exp_result = SIMPLE_STRNCMP (s1, s2, size);
+  FOR_EACH_IMPL (impl, 0)
+  check_result (impl, s1, s2, size, exp_result);
+}
+
+
 static void
 check_overflow (void)
 {
@@ -546,6 +569,7 @@  test_main (void)
   check1 ();
   check2 ();
   check3 ();
+  check4 ();
 
   printf ("%23s", "");
   FOR_EACH_IMPL (impl, 0)
diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
index 99e5349be8..07a5a2c889 100644
--- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
+++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
@@ -661,6 +661,7 @@  L(ret8):
 # ifdef USE_AS_STRNCMP
 	.p2align 4,, 10
 L(return_page_cross_end_check):
+	andl	%r10d, %ecx
 	tzcntl	%ecx, %ecx
 	leal	-VEC_SIZE(%rax, %rcx), %ecx
 	cmpl	%ecx, %edx
diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
index 6f42e3155a..56d8c118e4 100644
--- a/sysdeps/x86_64/multiarch/strcmp-evex.S
+++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
@@ -689,6 +689,7 @@  L(ret8):
 # ifdef USE_AS_STRNCMP
 	.p2align 4,, 10
 L(return_page_cross_end_check):
+	andl	%r10d, %ecx
 	tzcntl	%ecx, %ecx
 	leal	-VEC_SIZE(%rax, %rcx, SIZE_OF_CHAR), %ecx
 #  ifdef USE_AS_WCSCMP