Hi Jan,
On 28/04/2020 09:39, Jan Beulich wrote:
On 28.04.2020 10:24, George Dunlap wrote:
On Apr 28, 2020, at 8:20 AM, Jan Beulich <jbeul...@suse.com> 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
beginning.
I like the idea to have a more configurable Xen but this also comes at
the expense of the testing/support.
At the moment, we are getting around the problem by gating the new
config options with CONFIG_EXPERT. I have stoppped counting the number
of time I sweared because my config got rewritten when using 'make
clean' or explain to someone else how to use it.
As it stands, CONFIG_EXPERT is unusable and most likely anything behind
it will rot quite quickly. So if we want to add more stuff behind it,
then I would suggest to make it more accessible so any developper can
experiment with it.
Going forward, I would expect the embedded folks to want more part of
Xen configurable. Requesting them to use CONFIG_EXPERT may be an issue
as this means we would not security support them. At the same time, I
understand that exposing a CONFIG increase the testing matrix. How about
declaring we are supporting/testing a given set of .config? On Arm it
would be defconfig and tiny.
Cheers,
--
Julien Grall
