Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

H.J. Lu
2020-08-27T14:21:01Z

On Thu, Aug 27, 2020 at 7:07 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Thu, Aug 27, 2020 at 6:36 AM Florian Weimer <fweimer@redhat.com> wrote:
> >
> > * H. J. Lu:
> >
> > > On Thu, Aug 27, 2020 at 6:19 AM Florian Weimer <fweimer@redhat.com> wrote:
> > >>
> > >> * Dave Martin:
> > >>
> > >> > You're right that this has implications: for i386, libc probably pulls
> > >> > more arguments off the stack than are really there in some situations.
> > >> > This isn't a new problem though. There are already generic prctls with
> > >> > fewer than 4 args that are used on x86.
> > >>
> > >> As originally posted, glibc prctl would have to know that it has to pull
> > >> an u64 argument off the argument list for ARCH_X86_CET_DISABLE. But
> > >> then the u64 argument is a problem for arch_prctl as well.
> > >>
> > >
> > > Argument of ARCH_X86_CET_DISABLE is int and passed in register.
> >
> > The commit message and the C source say otherwise, I think (not sure
> > about the C source, not a kernel hacker).
>
> It should read:
>
> arch_prctl(ARCH_X86_CET_DISABLE, unsigned long features)
>

Or

arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features)

--
H.J.