Re: [Xen-devel] [PATCH v3 00/13] xen/arm: SSBD (aka Spectre-v4) mitigation (XSA-263)

[Julien Grall <julien.grall@xxxxxxx>]

On 06/12/2018 12:36 PM, Julien Grall wrote:
> Hi all,
>
> This patch series implement the Xen hypervisor side of the "Spectre-v4"
> (CVE-2018-3639) mitigation known as "Speculative Store Bypass Disable"
> (SSBD).
>
> More information can be found at:
>    https://bugs.chromium.org/p/project-zero/issues/detail?id=1528
>    
> https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability
>
> For all released Arm Cortex-A that are affected by this issue, then the
> preferred mitigation is simply to set a chicken bit in the firmware during
> CPU initialization and therefore no change to Xen is required. Other CPUs
> may require the chicken bit to be toggled dynamically (for example, when
> switching between kernel-mode and hypervisor-mode) and this is achieve by
> calling into EL3 via an SMC which has been published as part of the latest
> SMCCC specification:
>    
> https://developer.arm.com/cache-speculation-vulnerability-firmware-specification
>
> as well as an ATF update for the released ARM cores affected by SSBD:
>    https://github.com/ARM-software/arm-trusted-firmware/pull/1392
>
> These patches provide the following:
>    1. Safe probing of firmware to establish which CPUs in the system
>       require calling into EL3 as part of the mitigation
>    2. A command-line option to force SSBD mitigation to be always on,
>       always off, or dynamically toggled (default) for CPUs that require
>       the EL3 call.
>    3. An initial implementation of the call via Xen, which exposes the
>       mitigation to the guest via an HVC interface.
>
> This patch also provides bug fix and new infrastructure require to implement
> the mitigation:
>    1. Zeroed each vCPU stack
>    2. Provide generic assembly macros
>    3. Provide alternative callback (RFC)
>
> A branch can be found with all the patches at:
>    https://xenbits.xen.org/git-http/people/julieng/xen-unstable.git
>    branch ssbd/v3
I have merged the series into my next branch. I will merge it once the 
tree is opened.
Cheers,

--
Julien Grall

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