linux-kernel - [PATCH v4 3/4] x86: nVMX: check vmcs12->guest_ia32

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Message-ID: <20250515005353.952707-4-mlevitsk@redhat.com>
Date: Wed, 14 May 2025 20:53:52 -0400
From: Maxim Levitsky <mlevitsk@...hat.com>
To: kvm@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Sean Christopherson <seanjc@...gle.com>,
	Borislav Petkov <bp@...en8.de>,
	x86@...nel.org,
	Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v4 3/4] x86: nVMX: check vmcs12->guest_ia32_debugctl value given by L2

Check the vmcs12 guest_ia32_debugctl value before loading it, to avoid L2
being able to load arbitrary values to hardware IA32_DEBUGCTL.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 4 ++++
 arch/x86/kvm/vmx/vmx.c    | 2 +-
 arch/x86/kvm/vmx/vmx.h    | 2 ++
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index e073e3008b16..0bda6400e30a 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3193,6 +3193,10 @@ static int nested_vmx_check_guest_state(struct kvm_vcpu *vcpu,
 	     CC((vmcs12->guest_bndcfgs & MSR_IA32_BNDCFGS_RSVD))))
 		return -EINVAL;
 
+	if ((vmcs12->vm_entry_controls & VM_ENTRY_LOAD_DEBUG_CONTROLS) &&
+	     CC(vmcs12->guest_ia32_debugctl & ~vmx_get_supported_debugctl(vcpu, false)))
+		return -EINVAL;
+
 	if (nested_check_guest_non_reg_state(vmcs12))
 		return -EINVAL;
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9953de0cb32a..9046ee2e9a04 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2179,7 +2179,7 @@ static u64 nested_vmx_truncate_sysenter_addr(struct kvm_vcpu *vcpu,
 	return (unsigned long)data;
 }
 
-static u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated)
+u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated)
 {
 	u64 debugctl = 0;
 
diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
index 6d1e40ecc024..1b80479505d3 100644
--- a/arch/x86/kvm/vmx/vmx.h
+++ b/arch/x86/kvm/vmx/vmx.h
@@ -413,7 +413,9 @@ static inline void vmx_set_intercept_for_msr(struct kvm_vcpu *vcpu, u32 msr,
 		vmx_disable_intercept_for_msr(vcpu, msr, type);
 }
 
+
 void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu);
+u64 vmx_get_supported_debugctl(struct kvm_vcpu *vcpu, bool host_initiated);
 
 /*
  * Note, early Intel manuals have the write-low and read-high bitmap offsets
-- 
2.46.0