This is a note to let you know that I've just added the patch titled
KVM: x86/mmu: Fix write-protection of PTs mapped by the TDP MMU
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-x86-mmu-fix-write-protection-of-pts-mapped-by-the-tdp-mmu.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 7c8a4742c4abe205ec9daf416c9d42fd6b406e8e Mon Sep 17 00:00:00 2001
From: David Matlack <dmatlack@xxxxxxxxxx>
Date: Thu, 13 Jan 2022 23:30:17 +0000
Subject: KVM: x86/mmu: Fix write-protection of PTs mapped by the TDP MMU
From: David Matlack <dmatlack@xxxxxxxxxx>
commit 7c8a4742c4abe205ec9daf416c9d42fd6b406e8e upstream.
When the TDP MMU is write-protection GFNs for page table protection (as
opposed to for dirty logging, or due to the HVA not being writable), it
checks if the SPTE is already write-protected and if so skips modifying
the SPTE and the TLB flush.
This behavior is incorrect because it fails to check if the SPTE
is write-protected for page table protection, i.e. fails to check
that MMU-writable is '0'. If the SPTE was write-protected for dirty
logging but not page table protection, the SPTE could locklessly be made
writable, and vCPUs could still be running with writable mappings cached
in their TLB.
Fix this by only skipping setting the SPTE if the SPTE is already
write-protected *and* MMU-writable is already clear. Technically,
checking only MMU-writable would suffice; a SPTE cannot be writable
without MMU-writable being set. But check both to be paranoid and
because it arguably yields more readable code.
Fixes: 46044f72c382 ("kvm: x86/mmu: Support write protection for nesting in tdp MMU")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
Message-Id: <20220113233020.3986005-2-dmatlack@xxxxxxxxxx>
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/mmu/tdp_mmu.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1493,12 +1493,12 @@ static bool write_protect_gfn(struct kvm
!is_last_spte(iter.old_spte, iter.level))
continue;
- if (!is_writable_pte(iter.old_spte))
- break;
-
new_spte = iter.old_spte &
~(PT_WRITABLE_MASK | shadow_mmu_writable_mask);
+ if (new_spte == iter.old_spte)
+ break;
+
tdp_mmu_set_spte(kvm, &iter, new_spte);
spte_set = true;
}
Patches currently in stable-queue which might be from dmatlack@xxxxxxxxxx are
queue-5.15/kvm-x86-mmu-fix-write-protection-of-pts-mapped-by-the-tdp-mmu.patch
