linux-kernel - Re: [PATCH v2] arm64: Make kpti command line options x86 compatible

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Message-ID: <20181115154738.GB2062@brain-police>
Date:   Thu, 15 Nov 2018 15:47:39 +0000
From:   Will Deacon <will.deacon@....com>
To:     Alexander Graf <agraf@...e.de>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Richard Brown <rbrown@...e.de>,
        Matthias Brugger <mbrugger@...e.com>
Subject: Re: [PATCH v2] arm64: Make kpti command line options x86 compatible

On Tue, Nov 13, 2018 at 04:29:06PM +0100, Alexander Graf wrote:
> I've already stumbled over 2 cases where people got confused about how to
> disable kpti on AArch64. In both cases, they used existing x86_64 options
> and just applied that to an AArch64 system, expecting it to work.
> 
> I think it makes a lot of sense to have compatible kernel command line
> parameters whenever we can have them be compatible.
> 
> So this patch adds the pti= and no_pti kernel command line options, mapping
> them into the existing kpti= command line framework. It preserves the old
> syntax to maintain compatibility with older command lines.
> 
> While at it, the patch also marks the respective options as dual-arch.
> 
> Reported-by: Richard Brown <rbrown@...e.de>
> Signed-off-by: Alexander Graf <agraf@...e.de>
> 
> ---
> 
> v1 -> v2:
> 
>   - Actually make it compile. Sorry for the sloppy v1.
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  6 +++---
>  arch/arm64/kernel/cpufeature.c                  | 20 +++++++++++++++++++-
>  2 files changed, 22 insertions(+), 4 deletions(-)

This patch doesn't help though, right, because kpti= has already been
included with backports etc so the ship has sailed? Yeah, it's not ideal,
but we went over this before:

http://lists.infradead.org/pipermail/linux-arm-kernel/2018-August/598395.html

The thing we really need is the sysfs interface hooking up so you can easily
check the state of the mitigation. Still waiting for a follow-up on that ;)

http://lists.infradead.org/pipermail/linux-arm-kernel/2018-September/603412.html

Will