linux-kernel - [PATCH 5.4 199/475] KVM: x86/emulator: Defer not-present segment check in __load_segment

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Message-Id: <20220414110900.697455193@linuxfoundation.org>
Date:   Thu, 14 Apr 2022 15:09:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Hou Wenlong <houwenlong.hwl@...group.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 199/475] KVM: x86/emulator: Defer not-present segment check in __load_segment_descriptor()

From: Hou Wenlong <houwenlong.hwl@...group.com>

[ Upstream commit ca85f002258fdac3762c57d12d5e6e401b6a41af ]

Per Intel's SDM on the "Instruction Set Reference", when
loading segment descriptor, not-present segment check should
be after all type and privilege checks. But the emulator checks
it first, then #NP is triggered instead of #GP if privilege fails
and segment is not present. Put not-present segment check after
type and privilege checks in __load_segment_descriptor().

Fixes: 38ba30ba51a00 (KVM: x86 emulator: Emulate task switch in emulator.c)
Reviewed-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
Message-Id: <52573c01d369f506cadcf7233812427cf7db81a7.1644292363.git.houwenlong.hwl@...group.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/x86/kvm/emulate.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 60c8dcb907a5..ea48a2fb1677 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1714,11 +1714,6 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 		goto exception;
 	}
 
-	if (!seg_desc.p) {
-		err_vec = (seg == VCPU_SREG_SS) ? SS_VECTOR : NP_VECTOR;
-		goto exception;
-	}
-
 	dpl = seg_desc.dpl;
 
 	switch (seg) {
@@ -1758,6 +1753,10 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 	case VCPU_SREG_TR:
 		if (seg_desc.s || (seg_desc.type != 1 && seg_desc.type != 9))
 			goto exception;
+		if (!seg_desc.p) {
+			err_vec = NP_VECTOR;
+			goto exception;
+		}
 		old_desc = seg_desc;
 		seg_desc.type |= 2; /* busy */
 		ret = ctxt->ops->cmpxchg_emulated(ctxt, desc_addr, &old_desc, &seg_desc,
@@ -1782,6 +1781,11 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
 		break;
 	}
 
+	if (!seg_desc.p) {
+		err_vec = (seg == VCPU_SREG_SS) ? SS_VECTOR : NP_VECTOR;
+		goto exception;
+	}
+
 	if (seg_desc.s) {
 		/* mark segment as accessed */
 		if (!(seg_desc.type & 1)) {
-- 
2.34.1