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Message-ID: <c20d70acf5f5b0db5f52d6e163bb49f1235182f4.1728718232.git.isaku.yamahata@intel.com>
Date: Sat, 12 Oct 2024 00:39:55 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: kvm@...r.kernel.org,
pbonzini@...hat.com
Cc: Sean Christopherson <seanjc@...gle.com>,
sagis@...gle.com,
chao.gao@...el.com,
isaku.yamahata@...el.com,
rick.p.edgecombe@...el.com,
yan.y.zhao@...el.com,
linux-kernel@...r.kernel.org,
isaku.yamahata@...il.com
Subject: [PATCH v2 1/2] KVM: x86/tdp_mmu: Add WARN_ON_ONCE() in tdp_mmu_map_handle_target_level()
Add WARN_ON_ONCE() in tdp_mmu_map_handle_target_level() to check SPTE
validity made by make_spte() suggested at [1].
The possible SPTE change at present leaf is,
- Non leaf => leaf (large page).
- Read fault (SPTE doesn't have write permission) => write fault.
Hardening permission, write protect for example, goes through zapping.
- Access tracking when AD bits aren't supported.
- AD bit change. This should be removed when make_spte() is fixed [1].
[1] https://lore.kernel.org/kvm/ZuOCXarfAwPjYj19@google.com/
One idea would be to WARN and skip setting the SPTE in
tdp_mmu_map_handle_target_level(). I.e. WARN and ignore 1=>0 transitions
for Writable and Dirty bits, and then drop the TLB flush (assuming the
above patch lands).
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
v2:
- Split out into an independent patch to make common TDP MMU logic. (Sean)
---
arch/x86/kvm/mmu/spte.h | 11 +++++++++++
arch/x86/kvm/mmu/tdp_mmu.c | 14 +++++++++++++-
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index a72f0e3bde17..85fd99c92960 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -214,6 +214,17 @@ extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
*/
#define FROZEN_SPTE (SHADOW_NONPRESENT_VALUE | 0x5a0ULL)
+#define AD_SPTE_IGNORE_CHANGE_MASK \
+ (PT_WRITABLE_MASK | \
+ shadow_host_writable_mask | shadow_mmu_writable_mask | \
+ shadow_dirty_mask | shadow_accessed_mask)
+
+#define ACCESS_TRACK_SPTE_IGNORE_CHANGE_MASK \
+ (AD_SPTE_IGNORE_CHANGE_MASK | \
+ shadow_acc_track_mask | \
+ (SHADOW_ACC_TRACK_SAVED_BITS_MASK << \
+ SHADOW_ACC_TRACK_SAVED_BITS_SHIFT))
+
/* Removed SPTEs must not be misconstrued as shadow present PTEs. */
static_assert(!(FROZEN_SPTE & SPTE_MMU_PRESENT_MASK));
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 37b3769a5d32..1da3df517522 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1186,11 +1186,23 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
if (unlikely(!fault->slot))
new_spte = make_mmio_spte(vcpu, iter->gfn, ACC_ALL);
- else
+ else {
wrprot = make_spte(vcpu, sp, fault->slot, ACC_ALL, iter->gfn,
fault->pfn, iter->old_spte, fault->prefetch, true,
fault->map_writable, &new_spte);
+ WARN_ON_ONCE(kvm_ad_enabled() &&
+ is_shadow_present_pte(iter->old_spte) &&
+ is_large_pte(iter->old_spte) == is_large_pte(new_spte) &&
+ ~AD_SPTE_IGNORE_CHANGE_MASK &
+ (iter->old_spte ^ new_spte));
+ WARN_ON_ONCE(!kvm_ad_enabled() &&
+ is_shadow_present_pte(iter->old_spte) &&
+ is_large_pte(iter->old_spte) == is_large_pte(new_spte) &&
+ ~ACCESS_TRACK_SPTE_IGNORE_CHANGE_MASK &
+ (iter->old_spte ^ new_spte));
+ }
+
if (new_spte == iter->old_spte)
ret = RET_PF_SPURIOUS;
else if (tdp_mmu_set_spte_atomic(vcpu->kvm, iter, new_spte))
--
2.45.2
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