From: Sunil Pandey <skpgkp2@gmail.com>
To: "Carlos O'Donell" <carlos@redhat.com>,
Libc-stable Mailing List <libc-stable@sourceware.org>
Cc: Noah Goldstein <goldstein.w.n@gmail.com>,
libc-alpha@sourceware.org, hjl.tools@gmail.com,
carlos@systemhalted.org
Subject: Re: [PATCH v2] x86: Fix strncat-avx2.S reading past length [BZ #30065]
Date: Sat, 11 Feb 2023 17:00:06 -0800 [thread overview]
Message-ID: <CAMAf5_fvP10j59vDsfD9sMyXuHD_ViMHLVf4ONTR1_RGstp5+A@mail.gmail.com> (raw)
In-Reply-To: <f3f917b0-ab3b-54d5-4918-d5e417dfc1ca@redhat.com>
On Tue, Jan 31, 2023 at 7:10 PM Carlos O'Donell via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On 1/31/23 18:46, Noah Goldstein via Libc-alpha wrote:
> > Occurs when `src` has no null-term.
>
> This has been pushed as b2c474f8de4c92bfe7435853a96805ec32d68dfa.
>
> We are now in a hard freeze as I prepare to cut the release.
>
> Please do not commit anything further.
>
> If we find other issues we can backport to the release branch after testing.
>
> I'm re-running testing with this patch included for x86_64 and i686.
>
> > Two cases:
> >
> > 1) Zero-length check is doing:
> > ```
> > test %rdx, %rdx
> > jl L(zero_len)
> > ```
> > which doesn't actually check zero (was at some point `decq` and the
> > flag never got updated).
> >
> > The fix is just make the flag `jle` i.e:
> > ```
> > test %rdx, %rdx
> > jle L(zero_len)
> > ```
> >
> > 2) Length check in page-cross case checking if we should continue is
> > doing:
> > ```
> > cmpq %r8, %rdx
> > jb L(page_cross_small)
> > ```
> > which means we will continue searching for null-term if length ends at
> > the end of a page and there was no null-term in `src`.
> >
> > The fix is to make the flag:
> > ```
> > cmpq %r8, %rdx
> > jbe L(page_cross_small)
> > ```
> > ---
> > string/test-strncat.c | 25 ++++++++++++++++++++++++-
> > sysdeps/x86_64/multiarch/strncat-avx2.S | 4 ++--
> > 2 files changed, 26 insertions(+), 3 deletions(-)
> >
> > diff --git a/string/test-strncat.c b/string/test-strncat.c
> > index e03d329e1c..c0cde206ee 100644
> > --- a/string/test-strncat.c
> > +++ b/string/test-strncat.c
> > @@ -28,6 +28,7 @@
> > # define CHAR char
> > # define UCHAR unsigned char
> > # define SIMPLE_STRNCAT simple_strncat
> > +# define STRNLEN strnlen
> > # define STRLEN strlen
> > # define MEMSET memset
> > # define MEMCPY memcpy
> > @@ -40,6 +41,7 @@
> > # define CHAR wchar_t
> > # define UCHAR wchar_t
> > # define SIMPLE_STRNCAT simple_wcsncat
> > +# define STRNLEN wcsnlen
> > # define STRLEN wcslen
> > # define MEMSET wmemset
> > # define MEMCPY wmemcpy
> > @@ -78,7 +80,7 @@ do_one_test (impl_t *impl, CHAR *dst, const CHAR *src, size_t n)
> > return;
> > }
> >
> > - size_t len = STRLEN (src);
> > + size_t len = STRNLEN (src, n);
> > if (MEMCMP (dst + k, src, len + 1 > n ? n : len + 1) != 0)
> > {
> > error (0, 0, "Incorrect concatenation in function %s",
> > @@ -95,6 +97,26 @@ do_one_test (impl_t *impl, CHAR *dst, const CHAR *src, size_t n)
> > }
> > }
> >
> > +static void
> > +do_test_src_no_nullterm_bz30065 (void)
> > +{
> > + /* NB: "src does not need to be null-terminated if it contains n or more
> > + * bytes." */
> > + CHAR *s1, *s2;
> > + size_t bound = page_size / sizeof (CHAR);
> > + s1 = (CHAR *) (buf1 + BUF1PAGES * page_size);
> > + s2 = (CHAR *) buf2;
> > + MEMSET (s1 - bound, -1, bound);
> > + for (size_t n = 0; n < bound; ++n)
> > + {
> > + FOR_EACH_IMPL (impl, 0)
> > + {
> > + s2[0] = '\0';
> > + do_one_test (impl, s2, s1 - n, n);
> > + }
> > + }
> > +}
> > +
> > static void
> > do_test (size_t align1, size_t align2, size_t len1, size_t len2,
> > size_t n, int max_char)
> > @@ -372,6 +394,7 @@ test_main (void)
> >
> > do_random_tests ();
> > do_overflow_tests ();
> > + do_test_src_no_nullterm_bz30065 ();
> > return ret;
> > }
> >
> > diff --git a/sysdeps/x86_64/multiarch/strncat-avx2.S b/sysdeps/x86_64/multiarch/strncat-avx2.S
> > index b380e8e11c..c2ff202238 100644
> > --- a/sysdeps/x86_64/multiarch/strncat-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/strncat-avx2.S
> > @@ -66,7 +66,7 @@ ENTRY(STRNCAT)
> > salq $2, %rdx
> > # else
> > test %rdx, %rdx
> > - jl L(zero_len)
> > + jle L(zero_len)
> > # endif
> > vpxor %VZERO_128, %VZERO_128, %VZERO_128
> >
> > @@ -387,7 +387,7 @@ L(page_cross):
> > subl %esi, %r8d
> > andl $(VEC_SIZE - 1), %r8d
> > cmpq %r8, %rdx
> > - jb L(page_cross_small)
> > + jbe L(page_cross_small)
> >
> > /* Optimizing more aggressively for space as this is very cold
> > code. This saves 2x cache lines. */
>
> --
> Cheers,
> Carlos.
>
I would like to backport this patch to release branches.
Any comments or objections?
--Sunil
next parent reply other threads:[~2023-02-12 1:00 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230131213655.4033602-1-goldstein.w.n@gmail.com>
[not found] ` <20230131234656.2175991-1-goldstein.w.n@gmail.com>
[not found] ` <f3f917b0-ab3b-54d5-4918-d5e417dfc1ca@redhat.com>
2023-02-12 1:00 ` Sunil Pandey [this message]
2023-02-12 1:36 ` H.J. Lu
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