linux-kernel - Re: [PATCH v4 01/12] Documentation: Document arm64 kpti control

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Message-ID: <20190130180247.15ab0577@donnerap.cambridge.arm.com>
Date:   Wed, 30 Jan 2019 18:02:47 +0000
From:   Andre Przywara <andre.przywara@....com>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, stefan.wahren@...e.com,
        Jonathan Corbet <corbet@....net>, mlangsdo@...hat.com,
        linux-doc@...r.kernel.org, suzuki.poulose@....com,
        marc.zyngier@....com, catalin.marinas@....com,
        julien.thierry@....com, will.deacon@....com,
        linux-kernel@...r.kernel.org, steven.price@....com,
        ykaukab@...e.de, dave.martin@....com, shankerd@...eaurora.org
Subject: Re: [PATCH v4 01/12] Documentation: Document arm64 kpti control

On Fri, 25 Jan 2019 12:07:00 -0600
Jeremy Linton <jeremy.linton@....com> wrote:

Hi,

> For a while Arm64 has been capable of force enabling
> or disabling the kpti mitigations. Lets make sure the
> documentation reflects that.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> Cc: Jonathan Corbet <corbet@....net>
> Cc: linux-doc@...r.kernel.org
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt index
> b799bcf67d7b..9475f02c79da 100644 ---
> a/Documentation/admin-guide/kernel-parameters.txt +++
> b/Documentation/admin-guide/kernel-parameters.txt @@ -1982,6 +1982,12
> @@ Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
>  			the default is off.
>  
> +	kpti=		[ARM64] Control page table isolation of
> user
> +			and kernel address spaces.
> +			Default: enabled on cores which need
> mitigation.

Would this be a good place to mention that we enable it when
CONFIG_RANDOMIZE_BASE is enabled and we have a valid kaslr_offset? I
found this somewhat surprising, also it's unrelated to the
vulnerability.

Cheers,
Andre

> +			0: force disabled
> +			1: force enabled
> +
>  	kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled
> MSRs. Default is 0 (don't ignore, but inject #GP)
>