Re: PATCH? process_32.c:__switch_to() calls __math_state_restore() before updating current_task

[Oleg Nesterov <oleg@redhat.com>]

On 02/05, Oleg Nesterov wrote:
>
> In short: why restore_i387_xstate() does init_fpu() when !used_math(),
> can't (or shouldn't) it merely do set_used_math() ?
>
> 	restore_i387_xstate:
> 		
> 		if (!used_math()) {
> 			err = init_fpu(tsk);
> 			if (err)
> 				return err;
> 		}
>
> note that buf != NULL. This means that used_math() was true when
> get_sigframe() was called, otherwise buf == sigcontext->fpstate
> would be NULL, right?
>
> So, the task must have the valid ->thread.xstate,

This is probably correct. But a malicious user can set sc->fpsate
and fool the kernel, so we must assume buf != NULL implies the
valid ->xstate.

Oleg.