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

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Date:   Thu, 21 Sep 2023 22:22:54 +0000
From:   "Jitindar Singh, Suraj" <surajjs@...zon.com>
To:     "maz@...nel.org" <maz@...nel.org>
CC:     "vdonnefort@...gle.com" <vdonnefort@...gle.com>,
        "philmd@...aro.org" <philmd@...aro.org>,
        "james.morse@....com" <james.morse@....com>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        "oliver.upton@...ux.dev" <oliver.upton@...ux.dev>,
        "qperret@...gle.com" <qperret@...gle.com>,
        "kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "will@...nel.org" <will@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alexandru.elisei@....com" <alexandru.elisei@....com>
Subject: Re: [PATCH stable 6.1.y 1/2] KVM: arm64: Prevent the donation of
 no-map pages

On Thu, 2023-09-21 at 08:13 +0100, Marc Zyngier wrote:
> 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?

Noting any details about the backport. In this case it was a clean
backport.

> 
> > 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.
> 

The 2 patches were backported to address CVE-2023-21264.
This one provides context for the proceeding patch.

I wasn't aware that it's non functional. Does this mean that the code
won't be compiled or just that it can't actually be run currently from
the upstream codebase?

I guess I'm trying to understand if the conditions of the CVE are a
real concern even if it isn't technically functional.

Thanks

> Thanks,
> 
>         M.
>