[PATCH v2 1/6] arm: Add BTB invalidation on switch_mm for Cortex-A9, A12 and A17

[Marc Zyngier]

On 10/01/18 21:52, Nishanth Menon wrote:
> On 01/10/2018 11:57 AM, Marc Zyngier wrote:
>> On 10/01/18 17:53, Tony Lindgren wrote:
>>> * Marc Zyngier <marc.zyngier at arm.com> [180108 19:00]:
>>>> In order to avoid aliasing attacks against the branch predictor,
>>>> some implementations require to invalidate the BTB when switching
>>>> from one user context to another.
>>>>
>>>> For this, we reuse the existing implementation for Cortex-A8, and
>>>> apply it to A9, A12 and A17.
>>>
>>> I suspect we now must also make sure Cortex-A8 has the IBE bit
>>> set unconditionally for this to work. Currently the assumption is
>>> that IBE bit needs to be set only on the earlier CPU revisions
>>> that suffer from ARM_ERRATA_430973.
>>>
>>>> --- a/arch/arm/mm/proc-v7-2level.S
>>>> +++ b/arch/arm/mm/proc-v7-2level.S
>>>> @@ -41,7 +41,7 @@
>>>>    *	even on Cortex-A8 revisions not affected by 430973.
>>>>    *	If IBE is not set, the flush BTAC/BTB won't do anything.
>>>>    */
>>>> -ENTRY(cpu_ca8_switch_mm)
>>>> +ENTRY(cpu_v7_btbinv_switch_mm)
>>>>   #ifdef CONFIG_MMU
>>>>   	mov	r2, #0
>>>>   	mcr	p15, 0, r2, c7, c5, 6		@ flush BTAC/BTB
>>>
>>> So without IBE set, as the comments above say, the flush won't
>>> do anything.
>>
>> Indeed. Firmware/bootloaders must be updated to set IBE, just like on
>> Cortex-A15. I'll add a note to that effect.
> OK. in u-boot, I had helped on the following:
> http://git.denx.de/?p=u-boot.git;a=commitdiff;h=5902f4ce0f2bd1411e40dc0ece3598a0fc19b2ae
> 
> maybe be build off that?

Turn that into something unconditional, and you'll be good.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...