releases/3.17.3/kvm-x86-fix-far-jump-to-non-canonical-check.patch

From 7e46dddd6f6cd5dbf3c7bd04a7e75d19475ac9f2 Mon Sep 17 00:00:00 2001
From: Nadav Amit <namit@cs.technion.ac.il>
Date: Tue, 28 Oct 2014 00:03:43 +0200
Subject: KVM: x86: Fix far-jump to non-canonical check

From: Nadav Amit <namit@cs.technion.ac.il>

commit 7e46dddd6f6cd5dbf3c7bd04a7e75d19475ac9f2 upstream.

Commit d1442d85cc30 ("KVM: x86: Handle errors when RIP is set during far
jumps") introduced a bug that caused the fix to be incomplete.  Due to
incorrect evaluation, far jump to segment with L bit cleared (i.e., 32-bit
segment) and RIP with any of the high bits set (i.e, RIP[63:32] != 0) set may
not trigger #GP.  As we know, this imposes a security problem.

In addition, the condition for two warnings was incorrect.

Fixes: d1442d85cc30ea75f7d399474ca738e0bc96f715
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
[Add #ifdef CONFIG_X86_64 to avoid complaints of undefined behavior. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/emulate.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -573,12 +573,14 @@ static inline int assign_eip_far(struct
 	case 4:
 		ctxt->_eip = (u32)dst;
 		break;
+#ifdef CONFIG_X86_64
 	case 8:
 		if ((cs_l && is_noncanonical_address(dst)) ||
-		    (!cs_l && (dst & ~(u32)-1)))
+		    (!cs_l && (dst >> 32) != 0))
 			return emulate_gp(ctxt, 0);
 		ctxt->_eip = dst;
 		break;
+#endif
 	default:
 		WARN(1, "unsupported eip assignment size\n");
 	}
@@ -2026,7 +2028,7 @@ static int em_jmp_far(struct x86_emulate
 
 	rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l);
 	if (rc != X86EMUL_CONTINUE) {
-		WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64);
+		WARN_ON(ctxt->mode != X86EMUL_MODE_PROT64);
 		/* assigning eip failed; restore the old cs */
 		ops->set_segment(ctxt, old_sel, &old_desc, 0, VCPU_SREG_CS);
 		return rc;
@@ -2123,7 +2125,7 @@ static int em_ret_far(struct x86_emulate
 		return rc;
 	rc = assign_eip_far(ctxt, eip, new_desc.l);
 	if (rc != X86EMUL_CONTINUE) {
-		WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64);
+		WARN_ON(ctxt->mode != X86EMUL_MODE_PROT64);
 		ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS);
 	}
 	return rc;