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Date:   Fri, 29 Apr 2022 13:41:17 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jani Nikula <jani.nikula@linux.intel.com>
Cc:     David Gow <davidgow@google.com>,
        Brendan Higgins <brendanhiggins@google.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        "Guilherme G . Piccoli" <gpiccoli@igalia.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Sebastian Reichel <sre@kernel.org>,
        John Ogness <john.ogness@linutronix.de>,
        Joe Fradley <joefradley@google.com>,
        Daniel Latypov <dlatypov@google.com>,
        kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kunit: Taint kernel if any tests run
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References: <20220429043913.626647-1-davidgow@google.com>
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 <87tuacrv7t.fsf@intel.com>
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On Fri, Apr 29, 2022 at 02:21:26PM +0300, Jani Nikula wrote:
> On Fri, 29 Apr 2022, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Fri, Apr 29, 2022 at 12:39:14PM +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@google.com>
> >> ---
> >> 
> >> This is something I'd been thinking about for a while, and it came up
> >> again, so I'm finally giving it a go.
> >> 
> >> Two notes:
> >> - I decided to add a new type of taint, as none of the existing ones
> >>   really seemed to fit. We could live with considering KUnit tests as
> >>   TAINT_WARN or TAINT_CRAP or something otherwise, but neither are quite
> >>   right.
> >> - The taint_flags table gives a couple of checkpatch.pl errors around
> >>   bracket placement. I've kept the new entry consistent with what's
> >>   there rather than reformatting the whole table, but be prepared for
> >>   complaints about spaces.
> >> 
> >> Thoughts?
> >> -- David
> >> 
> >> ---
> >>  Documentation/admin-guide/tainted-kernels.rst | 1 +
> >>  include/linux/panic.h                         | 3 ++-
> >>  kernel/panic.c                                | 1 +
> >>  lib/kunit/test.c                              | 4 ++++
> >>  4 files changed, 8 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/Documentation/admin-guide/tainted-kernels.rst b/Documentation/admin-guide/tainted-kernels.rst
> >> index ceeed7b0798d..8f18fc4659d4 100644
> >> --- a/Documentation/admin-guide/tainted-kernels.rst
> >> +++ b/Documentation/admin-guide/tainted-kernels.rst
> >> @@ -100,6 +100,7 @@ Bit  Log  Number  Reason that got the kernel tainted
> >>   15  _/K   32768  kernel has been live patched
> >>   16  _/X   65536  auxiliary taint, defined for and used by distros
> >>   17  _/T  131072  kernel was built with the struct randomization plugin
> >> + 18  _/N  262144  a KUnit test has been run
> >>  ===  ===  ======  ========================================================
> >>  
> >>  Note: The character ``_`` is representing a blank in this table to make reading
> >> diff --git a/include/linux/panic.h b/include/linux/panic.h
> >> index f5844908a089..1d316c26bf27 100644
> >> --- a/include/linux/panic.h
> >> +++ b/include/linux/panic.h
> >> @@ -74,7 +74,8 @@ static inline void set_arch_panic_timeout(int timeout, int arch_default_timeout)
> >>  #define TAINT_LIVEPATCH			15
> >>  #define TAINT_AUX			16
> >>  #define TAINT_RANDSTRUCT		17
> >> -#define TAINT_FLAGS_COUNT		18
> >> +#define TAINT_KUNIT			18
> >> +#define TAINT_FLAGS_COUNT		19
> >>  #define TAINT_FLAGS_MAX			((1UL << TAINT_FLAGS_COUNT) - 1)
> >>  
> >>  struct taint_flag {
> >> diff --git a/kernel/panic.c b/kernel/panic.c
> >> index eb4dfb932c85..b24ca63ed738 100644
> >> --- a/kernel/panic.c
> >> +++ b/kernel/panic.c
> >> @@ -404,6 +404,7 @@ const struct taint_flag taint_flags[TAINT_FLAGS_COUNT] = {
> >>  	[ TAINT_LIVEPATCH ]		= { 'K', ' ', true },
> >>  	[ TAINT_AUX ]			= { 'X', ' ', true },
> >>  	[ TAINT_RANDSTRUCT ]		= { 'T', ' ', true },
> >> +	[ TAINT_KUNIT ]			= { 'N', ' ', false },
> >
> > As kunit tests can be in modules, shouldn't this be "true" here?
> >
> > Overall, I like it, makes sense to me.  The "N" will take some getting
> > used to, and I have no idea why "T" was for "struct randomization", that
> > would have allowed you to use "T" instead.  Oh well.
> 
> Would you consider a patch adding more self-explanatory taint flag
> strings to the output?

Where would those strings go?  In the oops report?  Or somewhere else?

thanks,

greg k-h