linux-kernel - [PATCH 3.13 106/162] KVM: x86: Fix far-jump to non-canonical check

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Message-Id: <1415313426-9622-107-git-send-email-kamal@canonical.com>
Date:	Thu,  6 Nov 2014 14:36:10 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Nadav Amit <namit@...technion.ac.il>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13 106/162] KVM: x86: Fix far-jump to non-canonical check

3.13.11.11 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nadav Amit <namit@...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@...cle.com>
Signed-off-by: Nadav Amit <namit@...technion.ac.il>
[Add #ifdef CONFIG_X86_64 to avoid complaints of undefined behavior. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
[ kamal: backport to 3.13-stable: omitted WARN_ON fixes (not in 3.13) ]
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 arch/x86/kvm/emulate.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index a440bea..4ae37e7 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -581,12 +581,14 @@ static inline int assign_eip_far(struct x86_emulate_ctxt *ctxt, ulong dst,
 	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");
 	}
-- 
1.9.1

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