linux-kernel - [73/75] KVM: Fix bounds checking in ioapic indirect register reads (CVE-2013-1798)

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Message-ID: <lsq.1366640759.822685429@decadent.org.uk>
Date:	Mon, 22 Apr 2013 15:25:59 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Andy Honig" <ahonig@...gle.com>,
	"Marcelo Tosatti" <mtosatti@...hat.com>
Subject: [73/75] KVM: Fix bounds checking in ioapic indirect register
 reads (CVE-2013-1798)

3.2.44-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Andy Honig <ahonig@...gle.com>

commit a2c118bfab8bc6b8bb213abfc35201e441693d55 upstream.

If the guest specifies a IOAPIC_REG_SELECT with an invalid value and follows
that with a read of the IOAPIC_REG_WINDOW KVM does not properly validate
that request.  ioapic_read_indirect contains an
ASSERT(redir_index < IOAPIC_NUM_PINS), but the ASSERT has no effect in
non-debug builds.  In recent kernels this allows a guest to cause a kernel
oops by reading invalid memory.  In older kernels (pre-3.3) this allows a
guest to read from large ranges of host memory.

Tested: tested against apic unit tests.

Signed-off-by: Andrew Honig <ahonig@...gle.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 virt/kvm/ioapic.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -73,9 +73,12 @@ static unsigned long ioapic_read_indirec
 			u32 redir_index = (ioapic->ioregsel - 0x10) >> 1;
 			u64 redir_content;
 
-			ASSERT(redir_index < IOAPIC_NUM_PINS);
+			if (redir_index < IOAPIC_NUM_PINS)
+				redir_content =
+					ioapic->redirtbl[redir_index].bits;
+			else
+				redir_content = ~0ULL;
 
-			redir_content = ioapic->redirtbl[redir_index].bits;
 			result = (ioapic->ioregsel & 0x1) ?
 			    (redir_content >> 32) & 0xffffffff :
 			    redir_content & 0xffffffff;

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