Re: [Xen-devel] [PATCH] don't put dom0 console info directly after start_info data

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.06.15 at 13:06, <"jgross@xxxxxxxx".non-mime.internet> wrote:
> The console information of dom0 is living in the same memory page as the
> start_info data. Don't put the console data directly after the start_info
> to leave some room for future structure enlargements. Otherwise a dom0
> with a newer start_info layout than the hypervisor could interprete
> console data as part of the start_info data.
> 
> Before commit 50bd1f0825339dfacde471df7664729216fc46e3 there used to be a
> padding at the end of start_info, but this was removed as it was regarded
> to be not necessary.

Said commit removed padding from shared_info, not start_info. Nor
would the suggested change be the correct one for a problem like
this. Instead the kernel should check how much of the shared info
structure it knows about is valid (which Dom0 can easily do using
console.dom0.info_off - that is, after all, why this is being placed at
a variable offset; DomU currently has no problem, as the rest of the
page is zero for it). If a future extension makes it so that this can't
be determined implicitly, a suitable SIF_* flag would need to be added.

Jan


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