On 5/2/23 06:59, Jan Beulich wrote:
On 02.05.2023 12:43, Daniel P. Smith wrote:
On 5/2/23 03:17, Jan Beulich wrote:
Unlike for XEN_DOMCTL_getdomaininfo, where the XSM check is intended to
cause the operation to fail, in the loop here it ought to merely
determine whether information for the domain at hand may be reported
back. Therefore if on the last iteration the hook results in denial,
this should not affect the sub-op's return value.
Fixes: d046f361dc93 ("Xen Security Modules: XSM")
Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
The hook being able to deny access to data for certain domains means
that no caller can assume to have a system-wide picture when holding the
results.
Wouldn't it make sense to permit the function to merely "count" domains?
While racy in general (including in its present, "normal" mode of
operation), within a tool stack this could be used as long as creation
of new domains is suppressed between obtaining the count and then using
it.
In XEN_DOMCTL_getpageframeinfo2 said commit had introduced a 2nd such
issue, but luckily that sub-op and xsm_getpageframeinfo() are long gone.
I understand there is a larger issue at play here but neutering the
security control/XSM check is not the answer. This literally changes the
way a FLASK policy that people currently have would be enforced, as well
as contrary to how they understand the access control that it provides.
Even though the code path does not fall under XSM maintainer, I would
NACK this patch. IMHO, it is better to find a solution that does not
abuse, misuse, or invalidate the purpose of the XSM calls.
On a side note, I am a little concern that only one person thought to
include the XSM maintainer, or any of the XSM reviewers, onto a patch
and the discussion around a patch that clearly relates to XSM for us to
gauge the consequences of the patch. I am not assuming intentions here,
only wanting to raise the concern.
Well, yes, for the discussion items I could have remembered to include
you. The code change itself, otoh, doesn't require your ack, even if it
is the return value of an XSM function which was used wrongly here.
I beg to disagree, not that you could have, but that you should have.
This is now the second XSM issue, that I am aware of at least, that
myself and the XSM reviewers have been left out of. How and where the
XSM hooks are deployed are critical to how XSM function, regardless of
how mundane the change may be. By your logic, as the XSM maintainer I
can make changes to the XSM code that changes how the system behaves for
x86 and claim you have no Ack/Nack authority since it is XSM code. These
subsystems are symbiotic, and we owe each other the due respect to
include to the other when these systems touch or influence each other.
So for what it is worth, NACK.
I'm puzzled: I hope you don't mean NACK to the patch (or effectively
Jürgen's identical one, which I had noticed only after sending mine).
Yet beyond that I don't see anything here which could be NACKed. I've
merely raised a couple of points for discussion.
I will comment on Jurgen's patch.
