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

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Date:   Fri, 29 Apr 2022 14:21:26 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        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>,
        "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        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
Subject: Re: [PATCH] kunit: Taint kernel if any tests run

On Fri, 29 Apr 2022, Greg KH <gregkh@...uxfoundation.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@...gle.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?

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Graphics Center