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: [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU races
Date: Fri, 3 Sep 2021 12:20:39 +0200 [thread overview]
Message-ID: <20210903102039.55422-4-eesposit@redhat.com> (raw)
In-Reply-To: <20210903102039.55422-1-eesposit@redhat.com>
Move the checks done by nested_vmcb_valid_sregs and
nested_vmcb_check_controls directly in enter_svm_guest_mode,
and use svm->nested.save cached fields (EFER, CR0, CR4)
instead of vmcb12's.
This prevents from creating TOC/TOU races.
This also avoids the need of force-setting EFER_SVME in
nested_vmcb02_prepare_save.
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
arch/x86/kvm/svm/nested.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 2491c77203c7..487810cfefde 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -280,13 +280,6 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu,
static bool nested_vmcb_valid_sregs(struct kvm_vcpu *vcpu,
struct vmcb_save_area *save)
{
- /*
- * FIXME: these should be done after copying the fields,
- * to avoid TOC/TOU races. For these save area checks
- * the possible damage is limited since kvm_set_cr0 and
- * kvm_set_cr4 handle failure; EFER_SVME is an exception
- * so it is force-set later in nested_prepare_vmcb_save.
- */
if (CC(!(save->efer & EFER_SVME)))
return false;
@@ -459,7 +452,8 @@ void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm)
svm->nested.vmcb02.ptr->save.g_pat = svm->vmcb01.ptr->save.g_pat;
}
-static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12)
+static void nested_vmcb02_prepare_save(struct vcpu_svm *svm,
+ struct vmcb *vmcb12)
{
bool new_vmcb12 = false;
@@ -488,15 +482,10 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
kvm_set_rflags(&svm->vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);
- /*
- * Force-set EFER_SVME even though it is checked earlier on the
- * VMCB12, because the guest can flip the bit between the check
- * and now. Clearing EFER_SVME would call svm_free_nested.
- */
- svm_set_efer(&svm->vcpu, vmcb12->save.efer | EFER_SVME);
+ svm_set_efer(&svm->vcpu, svm->nested.save.efer);
- svm_set_cr0(&svm->vcpu, vmcb12->save.cr0);
- svm_set_cr4(&svm->vcpu, vmcb12->save.cr4);
+ svm_set_cr0(&svm->vcpu, svm->nested.save.cr0);
+ svm_set_cr4(&svm->vcpu, svm->nested.save.cr4);
svm->vcpu.arch.cr2 = vmcb12->save.cr2;
@@ -671,7 +660,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
nested_load_control_from_vmcb12(svm, &vmcb12->control);
nested_load_save_from_vmcb12(svm, &vmcb12->save);
- if (!nested_vmcb_valid_sregs(vcpu, &vmcb12->save) ||
+ if (!nested_vmcb_valid_sregs(vcpu, &svm->nested.save) ||
!nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {
vmcb12->control.exit_code = SVM_EXIT_ERR;
vmcb12->control.exit_code_hi = 0;
--
2.27.0
next prev parent reply other threads:[~2021-09-03 10:21 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-03 10:20 [RFC PATCH 0/3] KVM: nSVM: avoid TOC/TOU race when checking vmcb12 Emanuele Giuseppe Esposito
2021-09-03 10:20 ` [RFC PATCH 1/3] KVM: nSVM: move nested_vmcb_check_cr3_cr4 logic in nested_vmcb_valid_sregs Emanuele Giuseppe Esposito
2021-09-12 10:36 ` Maxim Levitsky
2021-09-03 10:20 ` [RFC PATCH 2/3] nSVM: introduce smv->nested.save to cache save area fields Emanuele Giuseppe Esposito
2021-09-12 10:39 ` Maxim Levitsky
2021-09-28 16:20 ` Paolo Bonzini
2021-09-28 22:23 ` Sean Christopherson
2021-09-29 11:13 ` Paolo Bonzini
2021-09-03 10:20 ` Emanuele Giuseppe Esposito [this message]
2021-09-12 10:42 ` [RFC PATCH 3/3] nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU races Maxim Levitsky
2021-09-14 8:20 ` Emanuele Giuseppe Esposito
2021-09-14 9:02 ` Maxim Levitsky
2021-09-14 9:12 ` Maxim Levitsky
2021-09-14 9:24 ` Emanuele Giuseppe Esposito
2021-09-14 9:34 ` Maxim Levitsky
2021-09-14 10:52 ` Emanuele Giuseppe Esposito
2021-09-14 11:39 ` Maxim Levitsky
2021-09-28 16:21 ` Paolo Bonzini
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