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From:   Hou Wenlong <houwenlong93@linux.alibaba.com>
To:     kvm@vger.kernel.org
Cc:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/4] KVM: x86: Handle 32-bit wrap of EIP for EMULTYPE_SKIP with flat code seg
Date:   Tue,  2 Nov 2021 17:15:29 +0800
Message-Id: <093eabb1eab2965201c9b018373baf26ff256d85.1635842679.git.houwenlong93@linux.alibaba.com>
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From: Sean Christopherson <seanjc@google.com>

Truncate the new EIP to a 32-bit value when handling EMULTYPE_SKIP as the
decode phase does not truncate _eip.  Wrapping the 32-bit boundary is
legal if and only if CS is a flat code segment, but that check is
implicitly handled in the form of limit checks in the decode phase.

Opportunstically prepare for a future fix by storing the result of any
truncation in "eip" instead of "_eip".

Fixes: 1957aa63be53 ("KVM: VMX: Handle single-step #DB for EMULTYPE_SKIP on EPT misconfig")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ac83d873d65b..3d7fc5c21ceb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8124,7 +8124,12 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	 * updating interruptibility state and injecting single-step #DBs.
 	 */
 	if (emulation_type & EMULTYPE_SKIP) {
-		kvm_rip_write(vcpu, ctxt->_eip);
+		if (ctxt->mode != X86EMUL_MODE_PROT64)
+			ctxt->eip = (u32)ctxt->_eip;
+		else
+			ctxt->eip = ctxt->_eip;
+
+		kvm_rip_write(vcpu, ctxt->eip);
 		if (ctxt->eflags & X86_EFLAGS_RF)
 			kvm_set_rflags(vcpu, ctxt->eflags & ~X86_EFLAGS_RF);
 		return 1;
-- 
2.31.1