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

[Andy Whitcroft]

On Mon, May 20, 2013 at 01:06:36PM +0100, Luis Henriques wrote:
> From: Andy Honig <ahonig at google.com>
> 
> CVE-2013-1798
> 
> BugLink: https://bugs.launchpad.net/bugs/1158262
> 
> 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>
> (cherry picked from commit a2c118bfab8bc6b8bb213abfc35201e441693d55)
> 
> 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 9fe140b..69969ae 100644
> --- a/virt/kvm/ioapic.c
> +++ b/virt/kvm/ioapic.c
> @@ -71,9 +71,12 @@ 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;
> -- 

Simple upstream cherrypick of the above sha1.  Looks to return -1 for
invalid reads.

Acked-by: Andy Whitcroft <apw at canonical.com>

-apw