From mboxrd@z Thu Jan  1 00:00:00 1970
From: marc.zyngier@arm.com (Marc Zyngier)
Date: Mon, 8 Jan 2018 17:30:34 +0000
Subject: [PATCH 0/3] ARM branch predictor hardening
In-Reply-To: <20180108172435.GS3875@atomide.com>
References: <20180106120907.26701-1-marc.zyngier@arm.com>
 <20180108165425.GR3875@atomide.com>
 <0d7ac442-1112-33e9-1f1f-cd600c3e326d@arm.com>
 <20180108172435.GS3875@atomide.com>
Message-ID: <d129e6ea-36a3-95ef-a5ca-25366cf70e9d@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 08/01/18 17:24, Tony Lindgren wrote:
> * Marc Zyngier <marc.zyngier@arm.com> [180108 17:05]:
>> Hi Tony,
>>
>> On 08/01/18 16:54, Tony Lindgren wrote:
>>> * Marc Zyngier <marc.zyngier@arm.com> [180106 04:14]:
>>>> This small series implements some basic BP hardening by invalidating
>>>> the BTB on CPUs that are known to be susceptible to aliasing attacks.
>>>>
>>>> These patches are closely modelled against what we do on arm64,
>>>> although simpler as we can rely on an architected instruction to
>>>> perform the invalidation.
>>>>
>>>> The first patch reuses the Cortex-A8 BTB invalidation in switch_mm and
>>>> generalises it to be used on all affected CPUs. The second perform the
>>>> same invalidation on fatal signal delivery. The last one nukes it on
>>>> guest exit, and results in some major surgery (kudos to Dimitris
>>>> Papastamos who came up with the magic vector decoding sequence).
>>>
>>> So if a Cortex-A8 has bootloder set the IBE bit, and kernel has
>>> ARM_ERRATA_430973 enabled, is Cortex-A8 already hardened then?
>>
>> Almost. See the extra BTB invalidation in fault.c.
> 
> OK thanks. So for Cortex-A8, only patch "[PATCH 2/3] arm: Invalidate
> BTB on fatal signal for Cortex A8, A9, A12, A15 and A17" is needed
> if I read that right.

That's the idea. Although I'm about to change that patch as it's been
pointed out to me that I'm doing that in a preemptible context, which
makes it a bit dodgy.

I should have something to post later today, once I'm done with fixing
the Thumb2 build (which completely breaks on patch #3)...

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