Re: [PATCH v2 3/4] KVM: arm64: Sanitise MTE tags when a permission fault installs a mapping

[Catalin Marinas <catalin.marinas@arm.com>]

On Wed, Oct 21, 2026 at 12:06:59PM +0100, Fuad Tabba wrote:
> The stage-2 fault path sanitises MTE tags only on translation faults, as
> a permission fault normally just relaxes an existing leaf. However, when
> the page is backed by a THP, a permission fault at page granule installs
> a block whose other pages may never have been mapped or sanitised. Once
> dirty logging is off, a guest write to a page mapped read-only during
> logging installs the block, and the guest can read the tags those pages'
> previous owners left.
> 
> Sanitise whenever the fault path calls kvm_pgtable_stage2_map() rather
> than relaxing permissions. If the VMM replaces the VMA after the guest
> takes a permission fault but before vma_lookup(), that path would map
> and sanitise memory from the new VMA without checking it. Run the
> VM_MTE_ALLOWED check in kvm_s2_fault_compute_prot() on permission
> faults too.
> 
> Fixes: ea7fc1bb1cd1b ("KVM: arm64: Introduce MTE VM feature")
> Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>