linux-kernel - [RFC PATCH 0/3] KVM: nSVM: avoid TOC/TOU race when checking vmcb12

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Message-Id: <20210903102039.55422-1-eesposit@redhat.com>
Date:   Fri,  3 Sep 2021 12:20:36 +0200
From:   Emanuele Giuseppe Esposito <eesposit@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org,
        Emanuele Giuseppe Esposito <eesposit@...hat.com>
Subject: [RFC PATCH 0/3] KVM: nSVM: avoid TOC/TOU race when checking vmcb12

Currently there is a TOC/TOU race between the check of vmcb12's
efer, cr0 and cr4 registers and the later save of their values in
svm_set_*, because the guest could modify the values in the meanwhile.

To solve this issue, this serie introuces and uses svm->nested.save
structure in enter_svm_guest_mode to save the current value of efer,
cr0 and cr4 and later use these to set the vcpu->arch.* state.

Patch 1 just refactor the code to simplify the next two patches,
patch 2 introduces svm->nested.save to cache the efer, cr0 and cr4 fields
and in patch 3 we use it to avoid TOC/TOU races.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@...hat.com>

---
v1 -> RFC:
- use svm->nested.save instead of local variables.
- not dependent anymore from "KVM: nSVM: remove useless kvm_clear_*_queue"
- simplified patches, we just use the struct and not move the check
  nearer to the TOU.

Emanuele Giuseppe Esposito (3):
  KVM: nSVM: move nested_vmcb_check_cr3_cr4 logic in
    nested_vmcb_valid_sregs
  nSVM: introduce smv->nested.save to cache save area fields
  nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU
    races

 arch/x86/kvm/svm/nested.c | 82 ++++++++++++++++++++-------------------
 arch/x86/kvm/svm/svm.c    |  1 +
 arch/x86/kvm/svm/svm.h    |  3 ++
 3 files changed, 47 insertions(+), 39 deletions(-)

-- 
2.27.0