Re: [Xen-devel] [PATCH 5/7] xen/arm32: Invalidate BTB on guest exit for Cortex A17 and 12

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 24 January 2018 at 22:22, Konrad Rzeszutek Wilk
<konrad.wilk@xxxxxxxxxx> wrote:
> On Fri, Jan 19, 2018 at 01:41:01PM +0000, Julien Grall wrote:
>> In order to avoid aliasing attackes agains the branch predictor, let's
>> invalidate the BTB on guest exist. This is made complicated by the fact
>> that we cannot take a branch invalidating the BTB.
>>
>> This is based on the first version posrted by Marc Zyngier on Linux-arm
>> mailing list (see [1]).
>>
>> This is part of XSA-254.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
>>
>> [1] https://www.spinics.net/lists/arm-kernel/msg627032.html
>> ---
>>  xen/arch/arm/arm32/entry.S | 55 
>> ++++++++++++++++++++++++++++++++++++++++++++++
>>  xen/arch/arm/cpuerrata.c   | 19 ++++++++++++++++
>>  2 files changed, 74 insertions(+)
>>
>> diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
>> index 54a1733f87..c6ec0aa399 100644
>> --- a/xen/arch/arm/arm32/entry.S
>> +++ b/xen/arch/arm/arm32/entry.S
>> @@ -160,6 +160,61 @@ GLOBAL(hyp_traps_vector)
>>          b trap_irq                      /* 0x18 - IRQ */
>>          b trap_fiq                      /* 0x1c - FIQ */
>>
>> +        .align 5
>
> Not .align 8?

.align 5 is following was we already have for the other vector table.

Per [1], this will make sure the base address of the table is a
multiple of 32 (one instruction per vector).

Cheers,

[1] https://ftp.gnu.org/old-gnu/Manuals/gas/html_chapter/as_7.html#SEC70



>

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