linux-kernel - Re: [PATCH v9 3/6] KVM: arm64: Block cacheable PFNMAP mapping

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Message-ID: <20250704134512.GF1410929@nvidia.com>
Date: Fri, 4 Jul 2025 10:45:12 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: ankita@...dia.com
Cc: maz@...nel.org, oliver.upton@...ux.dev, joey.gouly@....com,
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Subject: Re: [PATCH v9 3/6] KVM: arm64: Block cacheable PFNMAP mapping

On Sat, Jun 21, 2025 at 04:21:08AM +0000, ankita@...dia.com wrote:
> From: Ankit Agrawal <ankita@...dia.com>
> 
> Fixes a security bug due to mismatched attributes between S1 and
> S2 mapping.
> 
> Currently, it is possible for a region to be cacheable in the userspace
> VMA, but mapped non cached in S2. This creates a potential issue where
> the VMM may sanitize cacheable memory across VMs using cacheable stores,
> ensuring it is zeroed. However, if KVM subsequently assigns this memory
> to a VM as uncached, the VM could end up accessing stale, non-zeroed data
> from a previous VM, leading to unintended data exposure. This is a security
> risk.
> 
> Block such mismatch attributes case by returning EINVAL when userspace
> try to map PFNMAP cacheable. Only allow NORMAL_NC and DEVICE_*.
> 
> CC: Oliver Upton <oliver.upton@...ux.dev>
> CC: Catalin Marinas <catalin.marinas@....com>
> CC: Sean Christopherson <seanjc@...gle.com>
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> ---
>  arch/arm64/kvm/mmu.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)

Looks straightforward now

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason