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

H.J. Lu
2020-08-28T11:40:41Z

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.

--
H.J.