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

From: Sergey Dyasli <sergey.dyasli@citrix.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Doug Goldstein <cardoe@cardoe.com>
Cc: "sergey.dyasli@citrix.com >> Sergey Dyasli"
	<sergey.dyasli@citrix.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Xen-devel <xen-devel@lists.xen.org>,
	Jan Beulich <jbeulich@suse.com>,
	Ian Jackson <Ian.Jackson@citrix.com>,
	Daniel De Graaf <dgdegra@tycho.nsa.gov>
Subject: Re: [Xen-devel] [PATCH v2] xsm: hide detailed Xen version from unprivileged guests
Date: Tue, 14 Jan 2020 10:19:08 +0000	[thread overview]
Message-ID: <2f1e4eb2-1487-11ec-8a62-3c19372af4e5@citrix.com> (raw)
In-Reply-To: <52fcbff2-c175-745b-0c4a-d9ce6d4ae45e@citrix.com>

On 13/01/2020 14:40, Andrew Cooper wrote:
> On 13/01/2020 12:51, George Dunlap wrote:
>>   So Sergey's second patch:
>>  - Still denies XENVER_extraversion at the hypervisor level
>>  - Leaves the value returned by the hypervisor as "<denied>"
>>  - Filters the "<denied>" string at the hvmloader level, to prevent it
>> leaking into a GUI and scaring customers.
>
> The SMBios table isn't the only way XENVER_extraversion leaks up into
> the UI.
>
> XENVER_extraversion isn't the only source of redacted information
> leaking up into the UI.
>
> Linux for example exports it all via sysfs.  The windows drivers put
> XENVER_extraversion into several other logs.

I've found that /sys/hypervisor/version/extra returns "<denied>".
"<hidded>" would have looked better there.

>> Now we get to Andy's objection on the 10th:
>>
>> ---
>> 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.
>> ---
>>
>> Basically, Andy says that *anywhere* it might show up is way too scary,
>> even a guest dmesg log.
>>
>> Well, I disagree; I look in "dmesg" and I see loads of "scary" things.
>
> Just because dmesg is not an example of a good UI, doesn't mean its ok
> for us to make:
>
> Xen version: 4.14<denied> (preserve-AD)

And the above is indeed found in dmesg of PV domains (they have no SMbios).
"<hidden>" is not appropriate here indeed. It should be either "" or
generic ".0" IMHO.

--
Thanks,
Sergey

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