linux-kernel - [PATCH 0/2] KVM: nSVM: avoid TOC/TOU race when checking vmcb12

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Date:   Mon,  9 Aug 2021 16:53:41 +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>, 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: [PATCH 0/2] KVM: nSVM: avoid TOC/TOU race when checking vmcb12

Currently there is a TOC/TOU race between the first 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 1) moves the actual check nearer to the
usage (from nested_svm_vmrun to enter_svm_guest_mode), possible thanks
to the patch "KVM: nSVM: remove useless kvm_clear_*_queue"
and 2) adds local variables 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 refactors the code to simplify the second patch, where
we move the TOC nearer to the TOU and use local variables.

Based-on: <20210802125634.309874-1-pbonzini@...hat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@...hat.com>

Emanuele Giuseppe Esposito (2):
  KVM: nSVM: move nested_vmcb_check_cr3_cr4 logic in
    nested_vmcb_valid_sregs
  KVM: nSVM: temporarly save vmcb12's efer, cr0 and cr4 to avoid TOC/TOU
    races

 arch/x86/kvm/svm/nested.c | 99 ++++++++++++++++++---------------------
 1 file changed, 45 insertions(+), 54 deletions(-)

-- 
2.31.1