linux-kernel - [PATCH v2 3/7] KVM: nVMX: Explicitly check for valid guest state for !unrestricted guest

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Message-Id: <20200923184452.980-4-sean.j.christopherson@intel.com>
Date:   Wed, 23 Sep 2020 11:44:48 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Dan Cross <dcross@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: [PATCH v2 3/7] KVM: nVMX: Explicitly check for valid guest state for !unrestricted guest

Call guest_state_valid() directly instead of querying emulation_required
when checking if L1 is attempting VM-Enter with invalid guest state.
If emulate_invalid_guest_state is false, KVM will fixup segment regs to
avoid emulation and will never set emulation_required, i.e. KVM will
incorrectly miss the associated consistency checks because the nested
path stuffs segments directly into vmcs02.

Opportunsitically add Consistency Check tracing to make future debug
suck a little less.

Fixes: 2bb8cafea80bf ("KVM: vVMX: signal failure for nested VMEntry if emulation_required")
Fixes: 3184a995f782c ("KVM: nVMX: fix vmentry failure code when L2 state would require emulation")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/vmx/nested.c | 2 +-
 arch/x86/kvm/vmx/vmx.c    | 8 ++------
 arch/x86/kvm/vmx/vmx.h    | 9 +++++++++
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 171e34286908..a50714a86dde 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2573,7 +2573,7 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 	 * which means L1 attempted VMEntry to L2 with invalid state.
 	 * Fail the VMEntry.
 	 */
-	if (vmx->emulation_required) {
+	if (CC(!vmx_guest_state_valid(vcpu))) {
 		*entry_failure_code = ENTRY_FAIL_DEFAULT;
 		return -EINVAL;
 	}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 6f9a0c6d5dc5..e8480dbef881 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -341,7 +341,6 @@ static const struct kernel_param_ops vmentry_l1d_flush_ops = {
 };
 module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
 
-static bool guest_state_valid(struct kvm_vcpu *vcpu);
 static u32 vmx_segment_access_rights(struct kvm_segment *var);
 static __always_inline void vmx_disable_intercept_for_msr(unsigned long *msr_bitmap,
 							  u32 msr, int type);
@@ -1415,7 +1414,7 @@ static void vmx_vcpu_put(struct kvm_vcpu *vcpu)
 
 static bool emulation_required(struct kvm_vcpu *vcpu)
 {
-	return emulate_invalid_guest_state && !guest_state_valid(vcpu);
+	return emulate_invalid_guest_state && !vmx_guest_state_valid(vcpu);
 }
 
 unsigned long vmx_get_rflags(struct kvm_vcpu *vcpu)
@@ -3471,11 +3470,8 @@ static bool cs_ss_rpl_check(struct kvm_vcpu *vcpu)
  * not.
  * We assume that registers are always usable
  */
-static bool guest_state_valid(struct kvm_vcpu *vcpu)
+bool __vmx_guest_state_valid(struct kvm_vcpu *vcpu)
 {
-	if (enable_unrestricted_guest)
-		return true;
-
 	/* real mode guest state checks */
 	if (!is_protmode(vcpu) || (vmx_get_rflags(vcpu) & X86_EFLAGS_VM)) {
 		if (!rmode_segment_valid(vcpu, VCPU_SREG_CS))
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index d7ec66db5eb8..e147f180350f 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -343,6 +343,15 @@ void vmx_get_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 void vmx_set_segment(struct kvm_vcpu *vcpu, struct kvm_segment *var, int seg);
 u64 construct_eptp(struct kvm_vcpu *vcpu, unsigned long root_hpa,
 		   int root_level);
+
+bool __vmx_guest_state_valid(struct kvm_vcpu *vcpu);
+static inline bool vmx_guest_state_valid(struct kvm_vcpu *vcpu)
+{
+	if (enable_unrestricted_guest)
+		return true;
+
+	return __vmx_guest_state_valid(vcpu);
+}
 void update_exception_bitmap(struct kvm_vcpu *vcpu);
 void vmx_update_msr_bitmap(struct kvm_vcpu *vcpu);
 bool vmx_nmi_blocked(struct kvm_vcpu *vcpu);
-- 
2.28.0