From: "H.J. Lu" <hjl.tools@gmail.com>
To: Noah Goldstein <goldstein.w.n@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>,
"Carlos O'Donell" <carlos@systemhalted.org>
Subject: Re: [PATCH v1] x86: Fix bug in strncmp-evex and strncmp-avx2 [BZ #28895]
Date: Tue, 15 Feb 2022 08:44:12 -0800 [thread overview]
Message-ID: <CAMe9rOob7nKDJ0aR3FKJFKD8DFZSGvuDRa62d+M5rzjyjMhfkw@mail.gmail.com> (raw)
In-Reply-To: <CAFUsyfJh34bpxYbuo6SNuj6L4Yjc+HceJB6BmHm7dH0c3f1Ljg@mail.gmail.com>
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 :-).
--
H.J.
next prev parent reply other threads:[~2022-02-15 16:44 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-15 16:28 Noah Goldstein
2022-02-15 16:32 ` H.J. Lu
2022-02-15 16:42 ` Noah Goldstein
2022-02-15 16:44 ` H.J. Lu [this message]
2022-02-15 16:42 ` [PATCH v2] " Noah Goldstein
2022-02-15 16:45 ` H.J. Lu
2022-02-15 16:48 ` [PATCH v1] " Andreas Schwab
2022-02-15 16:49 ` Noah Goldstein
2022-02-15 17:04 ` Andreas Schwab
2022-02-15 17:24 ` Noah Goldstein
2022-02-15 17:23 ` [PATCH v3] " Noah Goldstein
2022-02-15 18:11 ` Andreas Schwab
2022-02-16 2:27 ` [PATCH v4] " Noah Goldstein
2022-02-16 2:28 ` H.J. Lu
2022-05-04 6:02 ` Sunil Pandey
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