Re: [PATCH] x86-64 memcmp: Use unsigned Jcc instructions on size

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Sat, Feb 2, 2019 at 6:57 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Since the size argument is unsigned. we should use unsigned Jcc
> > instructions, instead of signed to check size.
> >
> > Tested on x86-64 and x32, with and without --disable-multi-arch.
>
> Does this impact x86-64 at all (technically), consider that an object
> size larger than SSIZE_MAX would be undefined anyway?

I don't think we will hit it on x86-64.

> It seems that on x32, it can give incorrect results if the sign bit on
> the 64-bit register is set.  In this sense, it is similar to
> CVE-2019-6488 in impact, right?  If we decide to treat this as a

For x32, there is no invalid memory access.  It just gives the wrong
result.

> security vulnerability, we need a new CVE ID because the version range
> is different (bug 24155 was not fixed in the 2.29 release).
>

Since the wrong result from memcmp may lead to security vulnerability, we
should apply for CVE.

Thanks.

-- 
H.J.