linux-kernel - [PATCH 0/2] KVM: x86/mmu: nEPT X-only unsync bug fix

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Message-Id: <20220513195000.99371-1-seanjc@google.com>
Date:   Fri, 13 May 2022 19:49:58 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 0/2]  KVM: x86/mmu: nEPT X-only unsync bug fix

Fix a contrived bug where KVM can create a shadow-present SPTE with RWX=0
if L1 modifies an existing RX or RWX 4kb SPTE to be X-only and the combined
permissions for the upper level SPTEs yield !X.

Patch 2 adds a comment explaining why FNAME(sync_page) isn't repsonsible
for flushing synchronized entries that reduce protections, e.g. drop X
(or add NX).  Lack of a flush made me do a double-take and a lot of
staring.

Sean Christopherson (2):
  KVM: x86/mmu: Drop RWX=0 SPTEs during ept_sync_page()
  KVM: x86/mmu: Comment FNAME(sync_page) to document TLB flushing logic

 arch/x86/kvm/mmu/paging_tmpl.h | 18 +++++++++++++++++-
 arch/x86/kvm/mmu/spte.c        |  2 ++
 2 files changed, 19 insertions(+), 1 deletion(-)


base-commit: 2764011106d0436cb44702cfb0981339d68c3509
-- 
2.36.0.550.gb090851708-goog