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

H.J. Lu
2020-08-28T17:46:35Z

On Fri, Aug 28, 2020 at 10:39 AM Andy Lutomirski <luto@kernel.org> wrote:
>
> On Fri, Aug 28, 2020 at 4:38 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Thu, Aug 27, 2020 at 11:24 PM Florian Weimer <fweimer@redhat.com> wrote:
> > >
> > > * H. J. Lu:
> > >
> > > > Can you think of ANY issues of passing more arguments to arch_prctl?
> > >
> > > On x32, the glibc arch_prctl system call wrapper only passes two
> > > arguments to the kernel, and applications have no way of detecting that.
> > > musl only passes two arguments on all architectures. It happens to work
> > > anyway with default compiler flags, but that's an accident.
> >
> > In the current glibc, there is no arch_prctl wrapper for i386. There are
> > arch_prctl wrappers with 2 arguments for x86-64 and x32. But this isn't an
> > issue for glibc since glibc is both the provider and the user of the new
> > arch_prctl extension. Besides,
> >
> > long syscall(long number, ...);
> >
> > is always available.
>
> Userspace is probably full of tools and libraries that contain tables
> of system calls and their signatures. Think tracing, audit, container
> management, etc. I don't know how they will react to the addition of
> new arguments.

Yes, they need to be updated to understand other new operations
added for CET.

--
H.J.