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Re: [PATCH v7 08/12] xen: add /buildinfo/config entry to hypervisor filesystem

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: George Dunlap <George.Dunlap@xxxxxxxxxx>
  • Date: Tue, 28 Apr 2020 08:24:31 +0000
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  • Cc: Jürgen Groß <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Thread-topic: [PATCH v7 08/12] xen: add /buildinfo/config entry to hypervisor filesystem

> On Apr 28, 2020, at 8:20 AM, Jan Beulich <jbeulich@xxxxxxxx> wrote:
> On 27.04.2020 18:25, George Dunlap wrote:
>> If Jan is OK with it simply being outside CONFIG_EXPERT, then great.  But if 
>> he insists on some kind of testing for it to be outside of CONFIG_EXPERT, 
>> then again, the people who want it to be security supported should be the 
>> ones who do the work to make it happen.
> I don't understand this part, I'm afraid: Without a config option,
> the code is going to be security supported as long as it doesn't
> get marked otherwise (experimental or what not). With an option
> depending on EXPERT, what would become security unsupported is the
> non-default (i.e. disabled) setting. There's not a whole lot to
> test there, it's merely a formal consequence of our general rules.
> (Of course, over time dependencies of other code may develop on
> the information being available e.g. to Dom0 userland. Just like
> there's Linux userland code assuming the kernel config is
> available in certain ways [I don't necessarily mean the equivalent
> of hypfs here], to then use it in what I'd call abusive ways in at
> least some cases.)

Here’s an argument you might make:

“As a member of the security team, I don’t want to be on the hook for issuing 
XSAs for code which isn’t at least smoke-tested.  Therefore, I oppose any patch 
adding CONFIG_HYPFS outside of CONFIG_EXPERT, *unless* there is a concrete plan 
for getting regular testing for CONFIG_HYPFS=n.”

I’m not saying that’s an argument you *should* make.  But personally I don’t 
have a strong argument against such an argument. So, it seems to me, if you did 
make it, you have a reasonable chance of carrying your point.

Now consider this hypothetical universe where you made that argument and nobody 
opposed it.  In order to get a particular feature (CONFIG_HYPFS=n security 
supported), there is extra work that needs to be done (getting CONFIG_HYPFS=n 
tested regularly).  My point was, the expectation should be that the extra work 
will be done by the people who want or benefit from the feature; the series 
shouldn’t be blocked until Juergen implements CONFIG_HYPFS=n testing (since he 
doesn’t personally have a stake in that feature).

Now obviously, doing work to help someone else out in the community is of 
course a good thing to do; it builds goodwill, uses our aggregate resources 
more efficiently, and makes our community more enjoyable to work with.  But the 
goodwill primarily comes from the fact that it was done as a voluntary choice, 
not as a requirement.

Juergen was balking at having to do what he saw as extra work to implement 
CONFIG_HYPFS.  I wanted to make it clear that even though I see value in having 
CONFIG_HYPFS, *he* doesn’t have to do the work if he doesn’t want to (although 
it would certainly be appreciated if he did).  And this paragraph was extending 
the same principle into the hypothetical universe where someone insisted that 
CONFIG_HYPFS=n had to be tested before being security supported.

Hope that makes sense. :-)




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