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

[Jason Gunthorpe]

On Sat, Jun 21, 2025 at 04:21:08AM +0000, ankita@xxxxxxxxxx wrote:
> From: Ankit Agrawal <ankita@xxxxxxxxxx>
> 
> 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@xxxxxxxxx>
> CC: Catalin Marinas <catalin.marinas@xxxxxxx>
> CC: Sean Christopherson <seanjc@xxxxxxxxxx>
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/mmu.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)

Looks straightforward now

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason