On 30/10/2024 23:01, Jeff Xu wrote:
>> -static int restore_poe_context(struct user_ctxs *user)
>> +static int restore_poe_context(struct user_ctxs *user,
>> + struct user_access_state *ua_state)
>> {
>> u64 por_el0;
>> int err = 0;
>> @@ -282,7 +338,7 @@ static int restore_poe_context(struct user_ctxs *user)
>>
>> __get_user_error(por_el0, &(user->poe->por_el0), err);
>> if (!err)
>> - write_sysreg_s(por_el0, SYS_POR_EL0);
>> + ua_state->por_el0 = por_el0;
>>
>> return err;
>> }
>> @@ -850,7 +906,8 @@ static int parse_user_sigframe(struct user_ctxs *user,
>> }
>>
>> static int restore_sigframe(struct pt_regs *regs,
>> - struct rt_sigframe __user *sf)
>> + struct rt_sigframe __user *sf,
>> + struct user_access_state *ua_state)
>> {
>> sigset_t set;
>> int i, err;
>> @@ -899,7 +956,7 @@ static int restore_sigframe(struct pt_regs *regs,
>> err = restore_zt_context(&user);
>>
>> if (err == 0 && system_supports_poe() && user.poe)
>> - err = restore_poe_context(&user);
>> + err = restore_poe_context(&user, ua_state);
>>
>> return err;
>> }
>> @@ -908,6 +965,7 @@ SYSCALL_DEFINE0(rt_sigreturn)
>> {
>> struct pt_regs *regs = current_pt_regs();
>> struct rt_sigframe __user *frame;
>> + struct user_access_state ua_state;
>>
>> /* Always make any pending restarted system calls return -EINTR */
>> current->restart_block.fn = do_no_restart_syscall;
>> @@ -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?
This is not necessary because restore_sigframe() no longer writes to
POR_EL0. restore_poe_context() (above) now saves the original POR_EL0
value into ua_state, and it is restore_user_access_state() (called below
just before returning to userspace) that actually writes to POR_EL0,
after all uaccess is completed.
Having said that, I somehow missed the call to restore_altstack() when
writing the commit message, so these changes in sys_rt_sigreturn are in
fact necessary. Good catch! At least the patch itself should be doing
the right thing.
- Kevin
> similar as x86 change [1],
> the discussion for this happened in [2] [3]
>
> [1] https://lore.kernel.org/lkml/20240802061318.2140081-5-aruna.ramakrishna@xxxxxxxxxx/
> [2] https://lore.kernel.org/lkml/20240425210540.3265342-1-jeffxu@xxxxxxxxxxxx/
> [3] https://lore.kernel.org/lkml/d0162c76c25bc8e1c876aebe8e243ff2e6862359.camel@xxxxxxxxx/
>
> Thanks
> -Jeff
>
>
>> + restore_user_access_state(&ua_state);
>> +
>> return regs->regs[0];
