[PATCH v2 4/6] arm: Add icache invalidation on switch_mm for Cortex-A15

[f.fainelli@gmail.com (Florian Fainelli)]

On 01/08/2018 10:55 AM, Marc Zyngier wrote:
> In order to avoid aliasing attacks against the branch predictor,
> Cortex-A15 require to invalidate the BTB when switching
> from one user context to another. The only way to do so on this
> CPU is to perform an ICIALLU, having set ACTLR[0] to 1 from secure
> mode.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---

[snip]

> diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
> index f6adfe88ead2..0a2245b309e5 100644
> --- a/arch/arm/mm/proc-v7-3level.S
> +++ b/arch/arm/mm/proc-v7-3level.S
> @@ -71,6 +71,22 @@ ENTRY(cpu_v7_switch_mm)
>  ENDPROC(cpu_v7_switch_mm)
>  ENDPROC(cpu_v7_btbinv_switch_mm)
>  
> +/*
> + *	Cortex-A15 requires ACTLR[0] to be set from secure in order
> + *	for the icache invalidation to also invalidate the BTB.

Considering that writes are ignored when we don't have the correct
permission level, how about set try to set this bit from the
__v7_ca15mp_setup and __v7_b15mp_setup labels just like we are setting
the SMP_EN bit for the poor bastards out there stuck with possibly
frozen bootloaders/ATF?
-- 
Florian