linux-kernel - [PATCH v13 06/21] KVM: x86: Add fault checks for guest CR4.CET setting

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Message-ID: <20250821133132.72322-7-chao.gao@intel.com>
Date: Thu, 21 Aug 2025 06:30:40 -0700
From: Chao Gao <chao.gao@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: chao.gao@...el.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	hpa@...or.com,
	john.allen@....com,
	mingo@...hat.com,
	minipli@...ecurity.net,
	mlevitsk@...hat.com,
	pbonzini@...hat.com,
	rick.p.edgecombe@...el.com,
	seanjc@...gle.com,
	tglx@...utronix.de,
	weijiang.yang@...el.com,
	x86@...nel.org,
	xin@...or.com
Subject: [PATCH v13 06/21] KVM: x86: Add fault checks for guest CR4.CET setting

From: Yang Weijiang <weijiang.yang@...el.com>

Check potential faults for CR4.CET setting per Intel SDM requirements.
CET can be enabled if and only if CR0.WP == 1, i.e. setting CR4.CET ==
1 faults if CR0.WP == 0 and setting CR0.WP == 0 fails if CR4.CET == 1.

Co-developed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Reviewed-by: Chao Gao <chao.gao@...el.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Tested-by: Mathias Krause <minipli@...ecurity.net>
Tested-by: John Allen <john.allen@....com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
---
 arch/x86/kvm/x86.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 799ac76679c9..c363f7df279f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1173,6 +1173,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	    (is_64_bit_mode(vcpu) || kvm_is_cr4_bit_set(vcpu, X86_CR4_PCIDE)))
 		return 1;
 
+	if (!(cr0 & X86_CR0_WP) && kvm_is_cr4_bit_set(vcpu, X86_CR4_CET))
+		return 1;
+
 	kvm_x86_call(set_cr0)(vcpu, cr0);
 
 	kvm_post_set_cr0(vcpu, old_cr0, cr0);
@@ -1372,6 +1375,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			return 1;
 	}
 
+	if ((cr4 & X86_CR4_CET) && !kvm_is_cr0_bit_set(vcpu, X86_CR0_WP))
+		return 1;
+
 	kvm_x86_call(set_cr4)(vcpu, cr4);
 
 	kvm_post_set_cr4(vcpu, old_cr4, cr4);
-- 
2.47.3