[PATCH 2/5] KVM: SVM: check validity of VMCB when returning from SMM

[Paolo Bonzini]

The VMCB12 is stored in guest memory and can be mangled while in SMM; it
is then reloaded by svm_leave_smm(), but it is not checked again for
validity.

Move the check code out of vmx_set_nested_state()
(the other "not a VMLAUNCH/VMRESUME" path that emulates a nested vmentry)
and reuse it in svm_leave_smm().

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c | 12 ++++++++++--
 arch/x86/kvm/svm/svm.c    |  4 ++++
 arch/x86/kvm/svm/svm.h    |  1 +
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 7b61124051a7..de9906adb73b 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -419,6 +419,15 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu)
 	return __nested_vmcb_check_controls(vcpu, ctl);
 }
 
+int nested_svm_check_cached_vmcb12(struct kvm_vcpu *vcpu)
+{
+	if (!nested_vmcb_check_save(vcpu) ||
+	    !nested_vmcb_check_controls(vcpu))
+		return -EINVAL;
+
+	return 0;
+}
+
 /*
  * If a feature is not advertised to L1, clear the corresponding vmcb12
  * intercept.
@@ -1034,8 +1043,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 	nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
 	nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
 
-	if (!nested_vmcb_check_save(vcpu) ||
-	    !nested_vmcb_check_controls(vcpu)) {
+	if (nested_svm_check_cached_vmcb12(vcpu) < 0) {
 		vmcb12->control.exit_code    = SVM_EXIT_ERR;
 		vmcb12->control.exit_info_1  = 0;
 		vmcb12->control.exit_info_2  = 0;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 477fda63653b..95495048902c 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4890,6 +4890,10 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)
 	vmcb12 = map.hva;
 	nested_copy_vmcb_control_to_cache(svm, &vmcb12->control);
 	nested_copy_vmcb_save_to_cache(svm, &vmcb12->save);
+
+	if (nested_svm_check_cached_vmcb12(vcpu) < 0)
+		goto unmap_save;
+
 	ret = enter_svm_guest_mode(vcpu, smram64->svm_guest_vmcb_gpa, vmcb12, false);
 
 	if (ret)
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ebd7b36b1ceb..6942e6b0eda6 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -797,6 +797,7 @@ static inline int nested_svm_simple_vmexit(struct vcpu_svm *svm, u32 exit_code)
 
 int nested_svm_exit_handled(struct vcpu_svm *svm);
 int nested_svm_check_permissions(struct kvm_vcpu *vcpu);
+int nested_svm_check_cached_vmcb12(struct kvm_vcpu *vcpu);
 int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
 			       bool has_error_code, u32 error_code);
 int nested_svm_exit_special(struct vcpu_svm *svm);
-- 
2.53.0