Re: [Xen-devel] [PATCH 7/7] x86/mm: Prevent 32bit PV guests using out-of-range linear addresses

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 12.09.17 at 18:04, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 12/09/17 16:50, Jan Beulich wrote:
>>>>> On 12.09.17 at 14:14, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> The grant ABI uses 64 bit values, and allows a PV guest to specify linear
>>> addresses.  There is nothing interesting a 32bit PV guest can reference 
>>> which
>>> will pass an __addr_ok() check, but it should still get an error for trying.
>> While I'm all for tightening checks, I'm not sure we reasonably can:
>> Existing guests may (perhaps inadvertently) rely on this behavior,
>> and hence may break with the change. I think a prereq to this is to
>> have a command line option (or even a per-guest one) to control
>> strict vs relaxed argument checking behavior, and tie the extra
>> checks to that option being true.
> 
> At the moment, any attempt to use this behaviour will still cause a
> general error, because we cant locate an L1e mapping the out-of-range
> linear address.  Therefore, the guest wouldn't have had the grant
> operation succeed before.

Oh, good point.

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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