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

From: Doug Goldstein <cardoe@cardoe.com>
To: George Dunlap <george.dunlap@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Sergey Dyasli <sergey.dyasli@citrix.com>,
	xen-devel@lists.xen.org
Cc: Lars Kurth <lars.kurth@citrix.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Daniel De Graaf <dgdegra@tycho.nsa.gov>
Subject: Re: [Xen-devel] [PATCH v2] xsm: hide detailed Xen version from unprivileged guests
Date: Fri, 10 Jan 2020 21:55:03 -0600	[thread overview]
Message-ID: <cbe5fc46-4fc9-f905-3492-2abc34a8e12e@cardoe.com> (raw)
In-Reply-To: <5e6956a4-9b32-6fae-6fa5-cf72a627a3da@citrix.com>

On 1/10/20 9:28 AM, George Dunlap wrote:
> On 1/10/20 11:02 AM, Andrew Cooper wrote:
>> 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@citrix.com>
>>> ---
>>> 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@citrix.com>
>>> CC: George Dunlap <George.Dunlap@eu.citrix.com>
>>> CC: Ian Jackson <ian.jackson@eu.citrix.com>
>>> CC: Jan Beulich <jbeulich@suse.com>
>>> CC: Julien Grall <julien@xen.org>
>>> CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>> CC: Stefano Stabellini <sstabellini@kernel.org>
>>> CC: Wei Liu <wl@xen.org>
>>> CC: Daniel De Graaf <dgdegra@tycho.nsa.gov>
>>
>> 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.
> 
> This seems like a reasonable argument that "<denied>" causes issues.
> But that doesn't change the fact that "" also causes issues.
> 

I'd be curious to hear the case where the empty string causes issues.

--
Doug

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