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Date:   Thu, 21 Sep 2023 08:13:40 +0100
Message-ID: <878r903snv.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Suraj Jitindar Singh <surajjs@amazon.com>
Cc:     <stable@vger.kernel.org>, <james.morse@arm.com>,
        <alexandru.elisei@arm.com>, <suzuki.poulose@arm.com>,
        <oliver.upton@linux.dev>, <catalin.marinas@arm.com>,
        <linux-arm-kernel@lists.infradead.org>, <kvmarm@lists.linux.dev>,
        <kvmarm@lists.cs.columbia.edu>, <linux-kernel@vger.kernel.org>,
        <sjitindarsingh@gmail.com>, Quentin Perret <qperret@google.com>,
        Philippe =?UTF-8?B?TWF0aGlldS1EYXVkw6k=?= <philmd@linaro.org>,
        Vincent Donnefort <vdonnefort@google.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [PATCH stable 6.1.y 1/2] KVM: arm64: Prevent the donation of no-map pages
In-Reply-To: <20230920192729.694309-1-surajjs@amazon.com>
References: <20230920192729.694309-1-surajjs@amazon.com>
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On Wed, 20 Sep 2023 20:27:28 +0100,
Suraj Jitindar Singh <surajjs@amazon.com> wrote:
>=20
> From: Quentin Perret <qperret@google.com>
>=20
> commit 43c1ff8b75011bc3e3e923adf31ba815864a2494 upstream.
>=20
> 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.
>=20
> 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.
>=20
> Reviewed-by: Philippe Mathieu-Daud=C3=A9 <philmd@linaro.org>
> Tested-by: Vincent Donnefort <vdonnefort@google.com>
> Signed-off-by: Quentin Perret <qperret@google.com>
> Signed-off-by: Will Deacon <will@kernel.org>
> Signed-off-by: Marc Zyngier <maz@kernel.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@amazon.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.

--=20
Without deviation from the norm, progress is not possible.