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List:       kvm
Subject:    [PATCH 2/6] KVM: x86: Wrong error code on limit violation during emulation
From:       Nadav Amit <namit () cs ! technion ! ac ! il>
Date:       2014-09-30 17:49:15
Message-ID: 1412099359-5316-3-git-send-email-namit () cs ! technion ! ac ! il
[Download RAW message or body]

GP and SS exceptions deliver as error-code the segment selector if the
exception occurred when the segment is loaded.  However, if the exception
occurs during the memory access itself, due to limit violations, the error-code
should be zero.  Fix it.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/kvm/emulate.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index a46207a..13a1c76 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -621,7 +621,7 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
 	bool usable;
 	ulong la;
 	u32 lim;
-	u16 sel;
+	u16 sel, error_code = 0;
 	unsigned cpl;
 
 	la = seg_base(ctxt, addr.seg) + addr.ea;
@@ -634,14 +634,14 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
 		usable = ctxt->ops->get_segment(ctxt, &sel, &desc, NULL,
 						addr.seg);
 		if (!usable)
-			goto bad;
+			goto bad_sel;
 		/* code segment in protected mode or read-only data segment */
 		if ((((ctxt->mode != X86EMUL_MODE_REAL) && (desc.type & 8))
 					|| !(desc.type & 2)) && write)
-			goto bad;
+			goto bad_sel;
 		/* unreadable code segment */
 		if (!fetch && (desc.type & 8) && !(desc.type & 2))
-			goto bad;
+			goto bad_sel;
 		lim = desc_limit_scaled(&desc);
 		if ((ctxt->mode == X86EMUL_MODE_REAL) && !fetch &&
 		    (ctxt->d & NoBigReal)) {
@@ -664,15 +664,15 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
 		if (!(desc.type & 8)) {
 			/* data segment */
 			if (cpl > desc.dpl)
-				goto bad;
+				goto bad_sel;
 		} else if ((desc.type & 8) && !(desc.type & 4)) {
 			/* nonconforming code segment */
 			if (cpl != desc.dpl)
-				goto bad;
+				goto bad_sel;
 		} else if ((desc.type & 8) && (desc.type & 4)) {
 			/* conforming code segment */
 			if (cpl < desc.dpl)
-				goto bad;
+				goto bad_sel;
 		}
 		break;
 	}
@@ -682,11 +682,13 @@ static int __linearize(struct x86_emulate_ctxt *ctxt,
 		return emulate_gp(ctxt, 0);
 	*linear = la;
 	return X86EMUL_CONTINUE;
+bad_sel:
+	error_code = sel;
 bad:
 	if (addr.seg == VCPU_SREG_SS)
-		return emulate_ss(ctxt, sel);
+		return emulate_ss(ctxt, error_code);
 	else
-		return emulate_gp(ctxt, sel);
+		return emulate_gp(ctxt, error_code);
 }
 
 static int linearize(struct x86_emulate_ctxt *ctxt,
-- 
1.9.1

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