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Re: [Xen-devel] [PATCH SpectreV1+L1TF v6 6/9] is_control_domain: block speculation


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Norbert Manthey <nmanthey@xxxxxxxxx>
  • Date: Thu, 14 Feb 2019 14:45:16 +0100
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Martin Pohlack <mpohlack@xxxxxxxxx>, wipawel@xxxxxxxxx, Julien Grall <julien.grall@xxxxxxx>, David Woodhouse <dwmw@xxxxxxxxxxxx>, "Martin Mazein\(amazein\)" <amazein@xxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Julian Stecklina <jsteckli@xxxxxxxxx>, Bjoern Doebel <doebel@xxxxxxxxx>
  • Delivery-date: Thu, 14 Feb 2019 13:45:36 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 2/12/19 15:11, Jan Beulich wrote:
>>>> On 08.02.19 at 14:44, <nmanthey@xxxxxxxxx> wrote:
>> Checks of domain properties, such as is_hardware_domain or is_hvm_domain,
>> might be bypassed by speculatively executing these instructions. A reason
>> for bypassing these checks is that these macros access the domain
>> structure via a pointer, and check a certain field. Since this memory
>> access is slow, the CPU assumes a returned value and continues the
>> execution.
>>
>> In case an is_control_domain check is bypassed, for example during a
>> hypercall, data that should only be accessible by the control domain could
>> be loaded into the cache.
>>
>> Signed-off-by: Norbert Manthey <nmanthey@xxxxxxxxx>
>>
>> ---
>>
>> Notes:
>>   v6: Drop nospec.h include
> And this was because of what? I think it is good practice to include
> other headers which added definitions rely on, even if in practice
> _right now_ that header gets included already by other means. If
> there's some recursion in header dependencies, then it would have
> been nice if you had pointed out the actual issue.

The nospec.h header has been introduced by the commit "xen/sched:
Introduce domain_vcpu() helper" between my v4 and v6, so I had to drop
my include there. The sched.h file still includes the nospec.h file, I
just do not have to add it any more. I could have been a bit more
verbose in the notes section.

Best,
Norbert

>
> Jan
>
>



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