[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

On 28.04.20 13:23, George Dunlap wrote:

On Apr 28, 2020, at 9:39 AM, Jan Beulich <jbeulich@xxxxxxxx> wrote:

On 28.04.2020 10:24, George Dunlap wrote:
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. :-)

Yes, it does, thanks for the clarification. I can see what you describe
as a valid perspective to take, but really in my request to Jürgen I
took another: Now that we have Kconfig, additions of larger bodies of
code (possibly also just in terms of binary size) should imo generally
be questioned whether they want/need to be built for everyone. I.e. it
is not to be left to people being worried about binary sizes to arrange
for things to not be built, but for people contributing new but not
entirely essential code to consider making it option from the very

I think that’s a reasonable position to take, but needs to be balanced on the amount of work that 
this would actually require.  If it only requires adding a handful of #ifdef’s and maybe making a 
few stubs, then yes, asking the submitter to make the change makes sense.  But if it requires three dozen 
#ifdef’s throughout the code and a fairly major architectural change, then I think it’s 
reasonable for a submitter to push back.

I don’t really understand why Juergen thinks adding CONFIG_HYPFS would cause a 
lot of code churn; my argumentation here is based on the assumption that his 
assessment is correct.

The main problem I'm seeing is the setting of runtime parameters.

This will need a complete different set of macros for defining those
parameters, split across multiple patches. And I'm fairly sure I'll
need to touch each custom_runtime_param handling function, too, in
order not to add dead code.




Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.