Patch "KVM: SVM: load control fields from VMCB12 before checking them" has been added to the 5.10-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    KVM: SVM: load control fields from VMCB12 before checking them

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-svm-load-control-fields-from-vmcb12-before-checking-them.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From a58d9166a756a0f4a6618e4f593232593d6df134 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Wed, 31 Mar 2021 06:24:43 -0400
Subject: KVM: SVM: load control fields from VMCB12 before checking them

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

commit a58d9166a756a0f4a6618e4f593232593d6df134 upstream.

Avoid races between check and use of the nested VMCB controls.  This
for example ensures that the VMRUN intercept is always reflected to the
nested hypervisor, instead of being processed by the host.  Without this
patch, it is possible to end up with svm->nested.hsave pointing to
the MSR permission bitmap for nested guests.

This bug is CVE-2021-29657.

Reported-by: Felix Wilhelm <fwilhelm@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Fixes: 2fcf4876ada ("KVM: nSVM: implement on demand allocation of the nested state")
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -246,7 +246,7 @@ static bool nested_vmcb_check_controls(s
 	return true;
 }
 
-static bool nested_vmcb_checks(struct vcpu_svm *svm, struct vmcb *vmcb12)
+static bool nested_vmcb_check_save(struct vcpu_svm *svm, struct vmcb *vmcb12)
 {
 	struct kvm_vcpu *vcpu = &svm->vcpu;
 	bool vmcb12_lma;
@@ -271,7 +271,7 @@ static bool nested_vmcb_checks(struct vc
 	if (kvm_valid_cr4(&svm->vcpu, vmcb12->save.cr4))
 		return false;
 
-	return nested_vmcb_check_controls(&vmcb12->control);
+	return true;
 }
 
 static void load_nested_vmcb_control(struct vcpu_svm *svm,
@@ -454,7 +454,6 @@ int enter_svm_guest_mode(struct vcpu_svm
 	int ret;
 
 	svm->nested.vmcb12_gpa = vmcb12_gpa;
-	load_nested_vmcb_control(svm, &vmcb12->control);
 	nested_prepare_vmcb_save(svm, vmcb12);
 	nested_prepare_vmcb_control(svm);
 
@@ -501,7 +500,10 @@ int nested_svm_vmrun(struct vcpu_svm *sv
 	if (WARN_ON_ONCE(!svm->nested.initialized))
 		return -EINVAL;
 
-	if (!nested_vmcb_checks(svm, vmcb12)) {
+	load_nested_vmcb_control(svm, &vmcb12->control);
+
+	if (!nested_vmcb_check_save(svm, vmcb12) ||
+	    !nested_vmcb_check_controls(&svm->nested.ctl)) {
 		vmcb12->control.exit_code    = SVM_EXIT_ERR;
 		vmcb12->control.exit_code_hi = 0;
 		vmcb12->control.exit_info_1  = 0;


Patches currently in stable-queue which might be from pbonzini@xxxxxxxxxx are

queue-5.10/kvm-svm-load-control-fields-from-vmcb12-before-checking-them.patch
queue-5.10/kvm-svm-ensure-that-efer.svme-is-set-when-running-nested-guest-or-on-nested-vmexit.patch