linux-kernel - Re: [PATCH stable 6.1.y 1/2] KVM: arm64: Prevent the donation of no-map pages

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Message-ID: <878r903snv.wl-maz@kernel.org>
Date:   Thu, 21 Sep 2023 08:13:40 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Suraj Jitindar Singh <surajjs@...zon.com>
Cc:     <stable@...r.kernel.org>, <james.morse@....com>,
        <alexandru.elisei@....com>, <suzuki.poulose@....com>,
        <oliver.upton@...ux.dev>, <catalin.marinas@....com>,
        <linux-arm-kernel@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
        <kvmarm@...ts.cs.columbia.edu>, <linux-kernel@...r.kernel.org>,
        <sjitindarsingh@...il.com>, Quentin Perret <qperret@...gle.com>,
        Philippe Mathieu-Daudé <philmd@...aro.org>,
        Vincent Donnefort <vdonnefort@...gle.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH stable 6.1.y 1/2] KVM: arm64: Prevent the donation of no-map pages

On Wed, 20 Sep 2023 20:27:28 +0100,
Suraj Jitindar Singh <surajjs@...zon.com> wrote:
> 
> From: Quentin Perret <qperret@...gle.com>
> 
> commit 43c1ff8b75011bc3e3e923adf31ba815864a2494 upstream.
> 
> Memory regions marked as "no-map" in the host device-tree routinely
> include TrustZone carev-outs and DMA pools. Although donating such pages
> to the hypervisor may not breach confidentiality, it could be used to
> corrupt its state in uncontrollable ways. To prevent this, let's block
> host-initiated memory transitions targeting "no-map" pages altogether in
> nVHE protected mode as there should be no valid reason to do this in
> current operation.
> 
> Thankfully, the pKVM EL2 hypervisor has a full copy of the host's list
> of memblock regions, so we can easily check for the presence of the
> MEMBLOCK_NOMAP flag on a region containing pages being donated from the
> host.
> 
> Reviewed-by: Philippe Mathieu-Daudé <philmd@...aro.org>
> Tested-by: Vincent Donnefort <vdonnefort@...gle.com>
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> Signed-off-by: Will Deacon <will@...nel.org>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Link: https://lore.kernel.org/r/20221110190259.26861-8-will@kernel.org
> [ bp: clean ]

What is this?

> Signed-off-by: Suraj Jitindar Singh <surajjs@...zon.com>

What is the rationale for backporting this? It wasn't tagged as Cc: to
stable for a reason: pKVM isn't functional upstream, and won't be for
the next couple of cycles *at least*.

So at it stands, I'm against such a backport.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.