linux-kernel - Re: [PATCH v3 2/3] kunit: Taint the kernel when KUnit tests are run

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Message-ID: <CAGS_qxr54nYThsj6UhqX54JO5WnyJXVQURnNF1eCzGB+4GCKLA@mail.gmail.com>
Date:   Fri, 13 May 2022 12:08:46 -0700
From:   Daniel Latypov <dlatypov@...gle.com>
To:     David Gow <davidgow@...gle.com>
Cc:     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>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Sebastian Reichel <sre@...nel.org>,
        John Ogness <john.ogness@...utronix.de>,
        Joe Fradley <joefradley@...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>,
        Lucas De Marchi <lucas.demarchi@...el.com>,
        Aaron Tomlin <atomlin@...hat.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH v3 2/3] kunit: Taint the kernel when KUnit tests are run

On Fri, May 13, 2022 at 1:32 AM David Gow <davidgow@...gle.com> wrote:
>
> Make KUnit trigger the new TAINT_TEST taint when any KUnit test is run.
> Due to KUnit tests not being intended to run on production systems, and
> potentially causing problems (or security issues like leaking kernel
> addresses), the kernel's state should not be considered safe for
> production use after KUnit tests are run.
>
> Signed-off-by: David Gow <davidgow@...gle.com>

Tested-by: Daniel Latypov <dlatypov@...gle.com>

Looks good to me.

There's an edge case where we might have 0 suites or 0 tests and we
still taint the kernel, but I don't think we need to deal with that.
At the start of kunit_run_tests() is the cleanest place to do this.

I wasn't quite sure where this applied, but I manually applied the changes here.
Without this patch, this command exits fine:
$ ./tools/testing/kunit/kunit.py run --kernel_args=panic_on_taint=0x40000

With it, I get
[12:03:31] Kernel panic - not syncing: panic_on_taint set ...
[12:03:31] CPU: 0 PID: 1 Comm: swapper Tainted: G                 N
5.17.0-00001-gea9ee5e7aed8-dirty #60

I'm a bit surprised that it prints 'G' and not 'N', but this does seem
to be the right mask
$ python3 -c 'print(hex(1<<18))'
0x40000
and it only takes effect when this patch is applied.
I'll chalk that up to my ignorance of how taint works.