[PATCH v2 0/4] KVM: nSVM: avoid TOC/TOU race when checking vmcb12

From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
To: kvm@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Maxim Levitsky <mlevitsk@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org,
	Emanuele Giuseppe Esposito <eesposit@redhat.com>
Subject: [PATCH v2 0/4]  KVM: nSVM: avoid TOC/TOU race when checking vmcb12
Date: Fri, 17 Sep 2021 08:03:25 -0400	[thread overview]
Message-ID: <20210917120329.2013766-1-eesposit@redhat.com> (raw)

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 and 4 we use it to avoid TOC/TOU races.

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

---
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.

v2:
* svm->nested.save is a separate struct vmcb_save_area_cached,
  and not vmcb_save_area.
* update also vmcb02->cr3 with svm->nested.save.cr3 

Emanuele Giuseppe Esposito (4):
  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 vmcb_save_area_cached in nested_vmcb_valid_sregs()
  nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU
    races

 arch/x86/kvm/svm/nested.c | 95 +++++++++++++++++++++------------------
 arch/x86/kvm/svm/svm.c    |  1 +
 arch/x86/kvm/svm/svm.h    | 12 +++++
 3 files changed, 64 insertions(+), 44 deletions(-)

-- 
2.27.0