Re: XSA-351 causing Solaris-11 systems to panic during boot.

[boris.ostrovsky@xxxxxxxxxx]

On 12/17/20 12:49 PM, boris.ostrovsky@xxxxxxxxxx wrote:
> On 12/17/20 11:46 AM, Andrew Cooper wrote:
>> On 17/12/2020 16:25, boris.ostrovsky@xxxxxxxxxx wrote:
>>> On 12/17/20 2:40 AM, Jan Beulich wrote:
>>>> On 17.12.2020 02:51, boris.ostrovsky@xxxxxxxxxx wrote:
>>>> I think this is acceptable as a workaround, albeit we may want to
>>>> consider further restricting this (at least on staging), like e.g.
>>>> requiring a guest config setting to enable the workaround. 
>>> Maybe, but then someone migrating from a stable release to 4.15 will have 
>>> to modify guest configuration.
>>>
>>>
>>>> But
>>>> maybe this will need to be part of the MSR policy for the domain
>>>> instead, down the road. We'll definitely want Andrew's view here.
>>>>
>>>> Speaking of staging - before applying anything to the stable
>>>> branches, I think we want to have this addressed on the main
>>>> branch. I can't see how Solaris would work there.
>>> Indeed it won't. I'll need to do that as well (I misinterpreted the 
>>> statement in the XSA about only 4.14- being vulnerable)
>> It's hopefully obvious now why we suddenly finished the "lets turn all
>> unknown MSRs to #GP" work at the point that we did (after dithering on
>> the point for several years).
>>
>> To put it bluntly, default MSR readability was not a clever decision at all.
>>
>> There is a large risk that there is a similar vulnerability elsewhere,
>> given how poorly documented the MSRs are (and one contemporary CPU I've
>> got the manual open for has more than 6000 *documented* MSRs).  We did
>> debate for a while whether the readability of the PPIN MSRs was a
>> vulnerability or not, before eventually deciding not.


Can we do something like KVM's ignore_msrs (but probably return 0 on reads to 
avoid leaks from the system)? It would allow to deal with cases when a guest is 
suddenly unable to boot after hypervisor update (especially from pre-4.14). It 
won't help in all cases since some MSRs may be expected to be non-zero but I 
think it will cover large number of them. (and it will certainly do what Jan is 
asking above but will not be specific to this particular breakage)


-boris


>> Irrespective of what we do to fix this in Xen, has anyone fixed Solaris yet?
>
> I am not aware of anyone working on this (not that I would be).
>
>
> -boris
>