Re: [Qemu-devel] [RFC][PATCH 06/45] msix: Prevent bogus mask updates on MMIO accesses

[Michael S. Tsirkin]

On Mon, Oct 17, 2011 at 02:07:10PM +0200, Jan Kiszka wrote:
> On 2011-10-17 13:57, Michael S. Tsirkin wrote:
> > On Mon, Oct 17, 2011 at 01:23:46PM +0200, Jan Kiszka wrote:
> >> On 2011-10-17 13:10, Michael S. Tsirkin wrote:
> >>> On Mon, Oct 17, 2011 at 11:27:40AM +0200, Jan Kiszka wrote:
> >>>> Only accesses to the MSI-X table must trigger a call to
> >>>> msix_handle_mask_update or a notifier invocation.
> >>>>
> >>>> Signed-off-by: Jan Kiszka <address@hidden>
> >>>
> >>> Why would msix_mmio_write be called on an access
> >>> outside the table?
> >>
> >> Because it handles both the table and the PBA.
> > 
> > Hmm. Interesting. Is there a bug in how we handle PBA
> > updates then? If yes I'd like a separate patch for that
> > to apply to the stable tree.
> 
> I first thought it was a serious bug, but it just triggers if the guest
> write to PBA (which is very uncommon) and that actually triggers any
> spurious out-of-bounds vector injection. Highly unlikely.

Yes guests don't really use PBA ATM. But is there something
bad a malicious guest can do? For example, what if
msix_clr_pending gets invoked with this huge vector value?

It does seem serious ...


> > 
> > BTW, this code will go away if PBA can get stored separately?
> 
> Hmm - yeah, true. Likely it's moot to discuss this change then.
> 
> Jan
> 
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