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Re: [PATCH v3 2/7] xsm: remove the ability to disable flask

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
  • Date: Fri, 27 Aug 2021 09:42:02 -0400
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  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Fri, 27 Aug 2021 13:42:24 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 8/25/21 11:22 AM, Jan Beulich wrote:
> On 05.08.2021 16:06, Daniel P. Smith wrote:
>> On Linux when SELinux is put into permissive mode the descretionary access
>> controls are still in place. Whereas for Xen when the enforcing state of 
>> flask
>> is set to permissive, all operations for all domains would succeed, i.e. it
>> does not fall back to the default access controls. To provide a means to 
>> mimic
>> a similar but not equivalent behavior, a flask op is present to allow a
>> one-time switch back to the default access controls, aka the "dummy policy".
>> This patch removes this flask op to enforce a consistent XSM usage model 
>> that a
>> reboot of Xen is required to change the XSM policy module in use.
>> Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
> The primary reason you remove this is - aiui - that with alternatives
> patching there's technically not really a way back (would need to re-
> patch every patched location, or every hook would need to check whether
> state changed to disabled and if so chain on to the dummy function).
> This became sufficiently clear to me only when looking at the next
> patch. It would be nice if description also said why the change is
> needed. As it stands to me the description reads at best like something
> that people could have different views on (and initially I didn't mean
> to reply here, for not being convinced of the removal of functionality
> in the common case).
> Jan

Ack, I can expand further.




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