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

[Kevin Brodsky]

On 31/10/2024 10:33, Will Deacon wrote:
> 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?

Yes, that's correct, see my earlier reply [1].

- Kevin

[1]
https://lore.kernel.org/all/cd0e114d-57eb-4c90-bb6f-9abf0cc8920f@arm.com/