Re: [PATCH v2 23/39] x86: Introduce userspace API for CET enabling

Mike Rapoport
2022-10-06T18:50:59Z

On Mon, Oct 03, 2022 at 10:51:02PM +0000, Edgecombe, Rick P wrote:
> CC Mike about ptrace/CRIU question.
>
> On Mon, 2022-10-03 at 12:01 -0700, Kees Cook wrote:
> > On Thu, Sep 29, 2022 at 03:29:20PM -0700, Rick Edgecombe wrote:
> > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> > >
> > > Add three new arch_prctl() handles:
> > >
> > > - ARCH_CET_ENABLE/DISABLE enables or disables the specified
> > > feature. Returns 0 on success or an error.
> > >
> > > - ARCH_CET_LOCK prevents future disabling or enabling of the
> > > specified feature. Returns 0 on success or an error
> > >
> > > The features are handled per-thread and inherited over
> > > fork(2)/clone(2),
> > > but reset on exec().

...

> > > +#include <linux/sched.h>
> > > +#include <linux/bitops.h>
> > > +#include <asm/prctl.h>
> > > +
> > > +long cet_prctl(struct task_struct *task, int option, unsigned long
> > > features)
> > > +{
> > > + if (option == ARCH_CET_LOCK) {
> > > + task->thread.features_locked |= features;
> > > + return 0;
> > > + }
> > > +
> > > + /* Don't allow via ptrace */
> > > + if (task != current)
> > > + return -EINVAL;
> >
> > ... but locking _is_ allowed via ptrace? If that intended, it should
> > be
> > explicitly mentioned in the commit log and in a comment here.
>
> I believe CRIU needs to lock via ptrace as well. Maybe Mike can
> confirm.

Actually, I didn't use ptrace for locking, I did it with "plain"
arch_prctl().

I still can't say for sure CRIU won't need this, I didn't have time yet to
have a closer look at this set.

--
Sincerely yours,
Mike.