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Re: [Xen-devel] [PATCH v2] xsm: hide detailed Xen version from unprivileged guests


  • To: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 10 Jan 2020 11:02:52 +0000
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  • Cc: Lars Kurth <lars.kurth@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
  • Delivery-date: Fri, 10 Jan 2020 11:03:07 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 10/01/2020 10:37, Sergey Dyasli wrote:
> Hide the following information that can help identify the running Xen
> binary version: XENVER_extraversion, XENVER_compile_info, XENVER_changeset.
> Add explicit cases for XENVER_commandline and XENVER_build_id as well.
>
> Introduce xsm_filter_denied() to hvmloader to remove "<denied>" string
> from guest's DMI tables that otherwise would be shown in tools like
> dmidecode.
>
> Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
> ---
> v1 --> v2:
> - Added xsm_filter_denied() to hvmloader instead of modifying xen_deny()
> - Made behaviour the same for both Release and Debug builds
> - XENVER_capabilities is no longer hided
>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
> CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Julien Grall <julien@xxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>

I realise there are arguments over how to fix this, but we (the Xen
community) have already f*cked up once here, and this is doing so a
second time.

Nack.

Fixing it anywhere other than Xen is simply not appropriate.

The reason for this (which ought to be obvious, but I guess only to
those who actually do customer support) is basic human physiology. 
"denied" means something has gone wrong.  It scares people, and causes
them to seek help to change fix whatever is broken.

It is not appropriate for it to find its way into the guest in the first
place, and that includes turning up in `dmesg` and other logs, and
expecting guest runtime to filter for it is complete nonsense.

As said several times before, the empty string is completely fine ABI
wise, doesn't confuse customers, and really really does work in practice.

~Andrew

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