linux-kernel - [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment

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Message-Id: <5b7188e6388ac9f4567d14eab32db9adf3e00119.1644292363.git.houwenlong.hwl@antgroup.com>
Date:   Tue, 08 Feb 2022 17:34:05 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] KVM: x86/emulator: Move the unhandled outer privilege level logic of far return into __load_segment_descriptor()

Outer-privilege level return is not implemented in emulator,
move the unhandled logic into __load_segment_descriptor to
make it easier to understand why the checks for RET are
incomplete.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
---
 arch/x86/kvm/emulate.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 37c4213bdcc1..bd91b952eb0a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1631,9 +1631,14 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 		if (!(seg_desc.type & 8))
 			goto exception;
 
-		/* RET can never return to an inner privilege level. */
-		if (transfer == X86_TRANSFER_RET && rpl < cpl)
-			goto exception;
+		if (transfer == X86_TRANSFER_RET) {
+			/* RET can never return to an inner privilege level. */
+			if (rpl < cpl)
+				goto exception;
+			/* Outer-privilege level return is not implemented */
+			if (rpl > cpl)
+				return X86EMUL_UNHANDLEABLE;
+		}
 		if (transfer == X86_TRANSFER_RET || transfer == X86_TRANSFER_TASK_SWITCH) {
 			if (seg_desc.type & 4) {
 				/* conforming */
@@ -2228,9 +2233,6 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
 	rc = emulate_pop(ctxt, &cs, ctxt->op_bytes);
 	if (rc != X86EMUL_CONTINUE)
 		return rc;
-	/* Outer-privilege level return is not implemented */
-	if (ctxt->mode >= X86EMUL_MODE_PROT16 && (cs & 3) > cpl)
-		return X86EMUL_UNHANDLEABLE;
 	rc = __load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS, cpl,
 				       X86_TRANSFER_RET,
 				       &new_desc);
-- 
2.31.1