Re: [Xen-devel] [PATCH L1TF v9 7/7] common/grant_table: block speculative out-of-bound accesses

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 27.02.19 at 17:13, <nmanthey@xxxxxxxxx> wrote:
> Speculative execution is not blocked in case one of the following
> properties is true:
>  - path cannot be triggered by the guest
>  - path does not return to the guest
>  - path does not result in an out-of-bound access
>  - path cannot be executed repeatedly
> Only the combination of the above properties allows to actually leak
> continuous chunks of memory. Therefore, we only add the penalty of
> protective mechanisms in case a potential speculative out-of-bound
> access matches all the above properties.

While this is all fine, how do I match which of the reasons applies to
which of (in particular) the gt_version checks left alone? As said, the
reasoning here should specifically be detailed so it can be used as a
guiding reference when adding further conditionals to the code down
the road. And of course review is (more) difficult this way as well, as
(judging from prior conversations) we don't seem to necessarily
agree in our views in all places, and hence to discuss a possibly
questionable decision others also need to understand which of the
criteria you considered to match in the specific case.

Jan



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