[PATCHv3] arm64: Rework valid_user_regs

[Peter Maydell]

On 1 March 2016 at 12:47, Mark Rutland <mark.rutland at arm.com> wrote:
> On Tue, Feb 16, 2016 at 06:20:05PM +0000, Will Deacon wrote:
>> > +static int valid_native_regs(struct user_pt_regs *regs)
>> > +{
>> > +   regs->pstate &= ~SPSR_EL1_AARCH64_RES0_BITS;
>> > +
>> > +   if (user_mode(regs) && !(regs->pstate & PSR_MODE32_BIT) &&
>> > +       (regs->pstate & PSR_D_BIT) == 0 &&
>> > +       (regs->pstate & PSR_A_BIT) == 0 &&
>> > +       (regs->pstate & PSR_I_BIT) == 0 &&
>> > +       (regs->pstate & PSR_F_BIT) == 0) {
>> > +           return 1;
>> > +   }
>> > +
>> > +   /* Force PSR to a valid 64-bit EL0t */
>> > +   regs->pstate &= PSR_N_BIT | PSR_Z_BIT | PSR_C_BIT | PSR_V_BIT;
>>
>> Can we not just zap the pstate to PSR_MODE_EL0t and be done with it?
>
> I'm worried that some userspace might be relying on these being
> preserved.

This function is called as part of signal-return, right?
You clearly can't just zap the flag registers in that code
path, because you'd then be corrupting the flags of the
bit of userspace code that was interrupted by the signal.
(Or am I missing something?)

thanks
-- PMM