[PATCH v3 1/5] arm64: signal: Improve POR_EL0 handling to avoid uaccess failures

[Will Deacon]

Hi Jeff,

Thanks for chiming in!

On Wed, Oct 30, 2024 at 03:01:53PM -0700, Jeff Xu wrote:
> On Tue, Oct 29, 2024 at 7:46 AM Kevin Brodsky <kevin.brodsky at arm.com> wrote:
> >
> > TL;DR: reset POR_EL0 to "allow all" before writing the signal frame,
> > preventing spurious uaccess failures.

[...]

> > @@ -924,12 +982,14 @@ SYSCALL_DEFINE0(rt_sigreturn)
> >         if (!access_ok(frame, sizeof (*frame)))
> >                 goto badframe;
> >
> > -       if (restore_sigframe(regs, frame))
> > +       if (restore_sigframe(regs, frame, &ua_state))
> >                 goto badframe;
> >
> >         if (restore_altstack(&frame->uc.uc_stack))
> >                 goto badframe;
> >
> Do you need to move restore_altstack ahead of restore_sigframe?
> similar as x86 change [1],
> the discussion for this  happened  in [2] [3]
> 
> [1] https://lore.kernel.org/lkml/20240802061318.2140081-5-aruna.ramakrishna@oracle.com/
> [2] https://lore.kernel.org/lkml/20240425210540.3265342-1-jeffxu@chromium.org/
> [3] https://lore.kernel.org/lkml/d0162c76c25bc8e1c876aebe8e243ff2e6862359.camel@intel.com/
> 
> > +       restore_user_access_state(&ua_state);

The POR isn't restored until here ^^^, so I _think_ restore_altstack()
is fine where it is. Kevin, can you confirm, please?

Will