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| author | Sean Christopherson <seanjc@google.com> | 2022-05-13 21:49:59 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-06-08 10:47:08 +0200 |
| commit | 9fb3565743d58352f00964bf47213b88aff4bb82 (patch) | |
| tree | 288bfd1375fa54085ace14f70328e95cd8ee97d8 /arch/x86/kvm/mmu/spte.c | |
| parent | KVM: selftests: nSVM: Add svm_nested_soft_inject_test (diff) | |
| download | linux-9fb3565743d58352f00964bf47213b88aff4bb82.tar.xz linux-9fb3565743d58352f00964bf47213b88aff4bb82.zip | |
KVM: x86/mmu: Drop RWX=0 SPTEs during ept_sync_page()
All of sync_page()'s existing checks filter out only !PRESENT gPTE,
because without execute-only, all upper levels are guaranteed to be at
least READABLE. However, if EPT with execute-only support is in use by
L1, KVM can create an SPTE that is shadow-present but guest-inaccessible
(RWX=0) if the upper level combined permissions are R (or RW) and
the leaf EPTE is changed from R (or RW) to X. Because the EPTE is
considered present when viewed in isolation, and no reserved bits are set,
FNAME(prefetch_invalid_gpte) will consider the GPTE valid, and cause a
not-present SPTE to be created.
The SPTE is "correct": the guest translation is inaccessible because
the combined protections of all levels yield RWX=0, and KVM will just
redirect any vmexits to the guest. If EPT A/D bits are disabled, KVM
can mistake the SPTE for an access-tracked SPTE, but again such confusion
isn't fatal, as the "saved" protections are also RWX=0. However,
creating a useless SPTE in general means that KVM messed up something,
even if this particular goof didn't manifest as a functional bug.
So, drop SPTEs whose new protections will yield a RWX=0 SPTE, and
add a WARN in make_spte() to detect creation of SPTEs that will
result in RWX=0 protections.
Fixes: d95c55687e11 ("kvm: mmu: track read permission explicitly for shadow EPT page tables")
Cc: David Matlack <dmatlack@google.com>
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220513195000.99371-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/mmu/spte.c')
| -rw-r--r-- | arch/x86/kvm/mmu/spte.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c index b5960bbde7f7..cda1851ec155 100644 --- a/arch/x86/kvm/mmu/spte.c +++ b/arch/x86/kvm/mmu/spte.c @@ -129,6 +129,8 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, u64 spte = SPTE_MMU_PRESENT_MASK; bool wrprot = false; + WARN_ON_ONCE(!pte_access && !shadow_present_mask); + if (sp->role.ad_disabled) spte |= SPTE_TDP_AD_DISABLED_MASK; else if (kvm_mmu_page_ad_need_write_protect(sp)) |