[ 3.5.y.z extended stable ] Patch "KVM: Fix bounds checking in ioapic indirect register reads" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Thu Apr 11 09:09:44 UTC 2013

This is a note to let you know that I have just added a patch titled

    KVM: Fix bounds checking in ioapic indirect register reads

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see



>From 7d2891cde449076d4425e94c0c6a9ad6e9acd9b6 Mon Sep 17 00:00:00 2001
From: Andy Honig <ahonig at google.com>
Date: Wed, 20 Feb 2013 14:49:16 -0800
Subject: [PATCH] KVM: Fix bounds checking in ioapic indirect register reads

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 at google.com>
Signed-off-by: Marcelo Tosatti <mtosatti at redhat.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
 virt/kvm/ioapic.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index 26fd54d..fdb1faf 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -73,9 +73,12 @@ static unsigned long ioapic_read_indirect(struct kvm_ioapic *ioapic,
 			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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