linux-kernel - [PATCH 3.12 68/72] KVM: x86: Fix far-jump to non-canonical check

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Message-Id: <e4bcfa44c82cb5bcfb44a4722c80686096c2e181.1448283890.git.jslaby@suse.cz>
Date:	Mon, 23 Nov 2015 14:12:29 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Nadav Amit <namit@...technion.ac.il>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 68/72] KVM: x86: Fix far-jump to non-canonical check

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

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

===============

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>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/x86/kvm/emulate.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 8216f484398f..ffae11d0754a 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -582,12 +582,14 @@ 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");
 	}
@@ -2000,7 +2002,7 @@ static int em_jmp_far(struct x86_emulate_ctxt *ctxt)
 
 	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;
@@ -2084,7 +2086,7 @@ static int em_ret_far(struct x86_emulate_ctxt *ctxt)
 		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;
-- 
2.6.3

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