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

[Marc Zyngier]

On 09/01/18 14:14, Andre Przywara wrote:
> Hi,
> 
> On 08/01/18 18:55, Marc Zyngier wrote:
>> 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.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
>> ---
>>  arch/arm/mm/proc-v7-2level.S |  4 ++--
>>  arch/arm/mm/proc-v7-3level.S |  6 ++++++
>>  arch/arm/mm/proc-v7.S        | 30 +++++++++++++++---------------
>>  3 files changed, 23 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/arm/mm/proc-v7-2level.S b/arch/arm/mm/proc-v7-2level.S
>> index c6141a5435c3..0422e58b74e8 100644
>> --- 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
>> @@ -66,7 +66,7 @@ ENTRY(cpu_v7_switch_mm)
>>  #endif
>>  	bx	lr
>>  ENDPROC(cpu_v7_switch_mm)
>> -ENDPROC(cpu_ca8_switch_mm)
>> +ENDPROC(cpu_v7_btbinv_switch_mm)
>>  
>>  /*
>>   *	cpu_v7_set_pte_ext(ptep, pte)
>> diff --git a/arch/arm/mm/proc-v7-3level.S b/arch/arm/mm/proc-v7-3level.S
>> index 7d16bbc4102b..f6adfe88ead2 100644
>> --- a/arch/arm/mm/proc-v7-3level.S
>> +++ b/arch/arm/mm/proc-v7-3level.S
>> @@ -54,6 +54,11 @@
>>   * Set the translation table base pointer to be pgd_phys (physical address of
>>   * the new TTB).
>>   */
>> +ENTRY(cpu_v7_btbinv_switch_mm)
>> +#ifdef CONFIG_MMU
>> +	mov	r3, #0
> 
> As Robin pointed out correctly, BPIALL ignores Rt, so you can get rid of
> that line entirely (which is not matching the actual Rt below, btw).
> Might be worth to add a comment about this.
I know. I just kept it out of consistency with the existing Cortex-A8
workaround, which may or may not behave the same way (I don't have one
around to test...).

Thanks,

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