linux-kernel - [PATCH v2 05/11] KVM: x86: emulator: update the emulation mode after CR0 write

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Message-Id: <20220621150902.46126-6-mlevitsk@redhat.com>
Date:   Tue, 21 Jun 2022 18:08:56 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>, x86@...nel.org,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        Ingo Molnar <mingo@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v2 05/11] KVM: x86: emulator: update the emulation mode after CR0 write

CR0.PE toggles real/protected mode, thus its update
should update the emulation mode.

This is likely a benign bug because there is no writeback
of state, other than the RIP increment, and when toggling
CR0.PE, the CPU has to execute code from a very low memory address.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/emulate.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6f4632babc4cd8..002687d17f9364 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3659,11 +3659,22 @@ static int em_movbe(struct x86_emulate_ctxt *ctxt)
 
 static int em_cr_write(struct x86_emulate_ctxt *ctxt)
 {
-	if (ctxt->ops->set_cr(ctxt, ctxt->modrm_reg, ctxt->src.val))
+	int cr_num = ctxt->modrm_reg;
+	int r;
+
+	if (ctxt->ops->set_cr(ctxt, cr_num, ctxt->src.val))
 		return emulate_gp(ctxt, 0);
 
 	/* Disable writeback. */
 	ctxt->dst.type = OP_NONE;
+
+	if (cr_num == 0) {
+		/* CR0 write might have updated CR0.PE */
+		r = update_emulation_mode(ctxt);
+		if (r != X86EMUL_CONTINUE)
+			return r;
+	}
+
 	return X86EMUL_CONTINUE;
 }
 
-- 
2.26.3