KVM: Fix bounds checking in ioapic indirect register reads (CVE-2013-1798)

a2c118bf · Andy Honig <[email protected]> · 2013-02-20 14:49:16 -08:00

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 <[email protected]>
Signed-off-by: Marcelo Tosatti <[email protected]>

Commit: a2c118bfab8bc6b8bb213abfc35201e441693d55
Parents: 0b79459b

Changes

1 files changed · +5 −2

File	Status	Add	Del	Content
virt/kvm/ioapic.c	modified	+5	−2	View file

virt/kvm/ioapic.c

View file

diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
index ce82b94..5ba005c 100644
--- a/virt/kvm/ioapic.c
+++ b/virt/kvm/ioapic.c
@@ -74,9 +74,12 @@ 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;