linux-kernel - Re: [PATCH v2] kunit: Taint kernel if any tests run

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Message-ID: <YnKS3MwNxvEi73OP@bombadil.infradead.org>
Date:   Wed, 4 May 2022 07:51:08 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     David Gow <davidgow@...gle.com>,
        Shuah Khan <skhan@...uxfoundation.org>
Cc:     Lucas De Marchi <lucas.demarchi@...el.com>,
        Aaron Tomlin <atomlin@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Sebastian Reichel <sre@...nel.org>,
        John Ogness <john.ogness@...utronix.de>,
        Joe Fradley <joefradley@...gle.com>,
        Daniel Latypov <dlatypov@...gle.com>,
        kunit-dev@...glegroups.com, linux-kselftest@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH v2] kunit: Taint kernel if any tests run

On Tue, May 03, 2022 at 02:49:58PM +0800, David Gow wrote:
> On Mon, May 2, 2022 at 2:24 AM Luis Chamberlain <mcgrof@...nel.org> wrote:
> >
> > On Sun, May 01, 2022 at 11:22:38AM -0700, Luis Chamberlain wrote:
> > > On Sat, Apr 30, 2022 at 11:00:19AM +0800, David Gow wrote:
> > > > KUnit tests are not supposed to run on production systems: they may do
> > > > deliberately illegal things to trigger errors, and have security
> > > > implications (assertions will often deliberately leak kernel addresses).
> > > >
> > > > Add a new taint type, TAINT_KUNIT to signal that a KUnit test has been
> > > > run. This will be printed as 'N' (for kuNit, as K, U and T were already
> > > > taken).
> > > >
> > > > This should discourage people from running KUnit tests on production
> > > > systems, and to make it easier to tell if tests have been run
> > > > accidentally (by loading the wrong configuration, etc.)
> > > >
> > > > Signed-off-by: David Gow <davidgow@...gle.com>
> > >
> > > There is no reason to distinguish kunit from selftests if the result is
> > > the same: really make the kernel try really insane stupid things which
> > > may crash it or put it into a bad state.
> > >
> My initial thought is that KUnit is explicitly in-kernel testing,
> whereas kselftest is (at least somewhat) user-space based.

selftests has modules, although I am not sure if there are selftests
which do not load modules. Shuah?

> My personal
> feeling is that "doing weird stuff from userspace" is fundamentally
> different from "doing weird stuff in the kernel".

True.

> That being said, in
> practice many kselftest tests load modules which do strange things,
> and those could be in scope for something like that. I'd still err on
> the side of only having those tests (or specifically those modules)
> add the taint, rather than all selftests, but could be conveniced.

Yeah I think now that this can easily be added by having a special
new module info, MODULE_TAINTS(taint_flag). Then in check_modinfo()
you'd get_modinfo(info, "taints") to then add_taint_module() if set.

We can ignore the userspace thing I mentioned earlier as I thought
at first we could not add the taint to selftest modules easily but
we can.

  Luis