Re: [PATCH v5 05/27] arm64: Use daifflag_restore after bp_hardening

[Julien Thierry]

Hi James,

On 12/09/18 11:32, James Morse wrote:
> Hi Julien,
>
> On 28/08/18 16:51, Julien Thierry wrote:
> > For EL0 entries requiring bp_hardening, daif status is kept at
> > DAIF_PROCCTX_NOIRQ until after hardening has been done. Then interrupts
> > are enabled through local_irq_enable().
> >
> > Before using local_irq_* functions, daifflags should be properly restored
> > to a state where IRQs are enabled.
>
> > Enable IRQs by restoring DAIF_PROCCTX state after bp hardening.
>
> Is this just for symmetry, or are you going on to add something to the daifflags
> state that local_irq_* functions won't change? (if so, could you allude to that
> in the commit message)

What happens is that once we use ICC_PMR_EL1, local_irq_enable will not 
touch PSR.I. And we are coming back from an entry where PSR.I was kept 
to 1 so local_irq_enable was not actually enabling the interrupts. On 
the otherhand, restore will affect both.

Another option is to have the asm macro "enable_da_f" also switch to PMR 
usage (i.e. "just keep normal interrupts disabled"). Overall it would 
probably be easier to reason with, but I'm just unsure whether it is 
acceptable to receive a Pseudo NMI before having applied the bp_hardening.

If it is possible, I'm happy to solve this with enable_da_f.

Thanks,

> Either way,
>
> Acked-by: James Morse <james.morse@xxxxxxx>

--
Julien Thierry