[PATCH v3 2/7] x86: Fix __wcsncmp_evex in strcmp-evex.S [BZ# 28755]

[H.J. Lu]

On Mon, Jan 10, 2022 at 6:15 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Jan 10, 2022 at 1:36 PM Noah Goldstein via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
> >
> > Fixes [BZ# 28755] for wcsncmp by redirecting length >= 2^56 to
> > __wcscmp_evex. For x86_64 this covers the entire address range so any
> > length larger could not possibly be used to bound `s1` or `s2`.
> >
> > test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass.
> >
> > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> > ---
> >  sysdeps/x86_64/multiarch/strcmp-evex.S | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/sysdeps/x86_64/multiarch/strcmp-evex.S b/sysdeps/x86_64/multiarch/strcmp-evex.S
> > index 1d971f3889..0cd939d5af 100644
> > --- a/sysdeps/x86_64/multiarch/strcmp-evex.S
> > +++ b/sysdeps/x86_64/multiarch/strcmp-evex.S
> > @@ -104,6 +104,16 @@ ENTRY (STRCMP)
> >         je      L(char0)
> >         jb      L(zero)
> >  #  ifdef USE_AS_WCSCMP
> > +#  ifndef __ILP32__
> > +       movq    %rdx, %rcx
> > +       /* Check if length could overflow when multiplied by
> > +          sizeof(wchar_t). Checking top 8 bits will cover all potential
> > +          overflow cases as well as redirect cases where its impossible to
> > +          length to bound a valid memory region. In these cases just use
> > +          'wcscmp'.  */
> > +       shrq    $56, %rcx
> > +       jnz     __wcscmp_evex
> > +#  endif
> >         /* Convert units: from wide to byte char.  */
> >         shl     $2, %RDX_LP
> >  #  endif
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.

I am backporting this to 2.34 branch.

-- 
H.J.