linux-kernel - Re: [PATCH 08/11] arm64: KVM: Use per-CPU vector when BP hardening is enabled

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Date:   Thu, 4 Jan 2018 17:05:16 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/11] arm64: KVM: Use per-CPU vector when BP hardening is enabled

On 4 January 2018 at 17:04, Marc Zyngier <marc.zyngier@....com> wrote:
> On 04/01/18 16:28, Ard Biesheuvel wrote:
>> On 4 January 2018 at 15:08, Will Deacon <will.deacon@....com> wrote:
>>> From: Marc Zyngier <marc.zyngier@....com>
>>>
>>> Now that we have per-CPU vectors, let's plug then in the KVM/arm64 code.
>>>
>>
>> Why does bp hardening require per-cpu vectors?
>
> The description is not 100% accurate. We have per *CPU type* vectors.
> This stems from the following, slightly conflicting requirements:
>
> - We have systems with more than one CPU type (think big-little)
> - Different implementations require different BP hardening sequences
> - The BP hardening sequence must be executed before doing any branch
>
> The natural solution is to have one set of vectors per CPU type,
> containing the BP hardening sequence for that particular implementation,
> ending with a branch to the common code.
>

Crystal clear, thanks.