linux-kernel - Re: [PATCH] selftests/lkdtm: Use "comm" instead of "diff" for dmesg

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Date:   Wed, 9 Sep 2020 16:29:50 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Kees Cook <keescook@...omium.org>, Shuah Khan <shuah@...nel.org>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        Petr Mladek <pmladek@...e.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>
Subject: Re: [PATCH] selftests/lkdtm: Use "comm" instead of "diff" for dmesg

On 9/9/20 3:49 PM, Kees Cook wrote:
> 
> On Fri, Jun 26, 2020 at 01:59:43PM -0700, Kees Cook wrote:
>> Instead of full GNU diff (which smaller boot environments may not have),
>> use "comm" which is more available.
>>
>> Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
>> Link: https://lore.kernel.org/lkml/CA+G9fYtHP+Gg+BrR_GkBMxu2oOi-_e9pATtpb6TVRswv1G1r1Q@mail.gmail.com
>> Fixes: f131d9edc29d ("selftests/lkdtm: Don't clear dmesg when running tests")
>> Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> Shuah, this really needs to land to fix lkdtm tests on busybox. Can
> you add this to -next? (Or is it better to direct this to Greg for the
> lkdtm tree?)
> 
> Thanks!
> 
> -Kees
> 
>> ---
>>   tools/testing/selftests/lkdtm/run.sh | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/testing/selftests/lkdtm/run.sh b/tools/testing/selftests/lkdtm/run.sh
>> index 8383eb89d88a..5fe23009ae13 100755
>> --- a/tools/testing/selftests/lkdtm/run.sh
>> +++ b/tools/testing/selftests/lkdtm/run.sh
>> @@ -82,7 +82,7 @@ dmesg > "$DMESG"
>>   ($SHELL -c 'cat <(echo '"$test"') >'"$TRIGGER" 2>/dev/null) || true
>>   
>>   # Record and dump the results
>> -dmesg | diff --changed-group-format='%>' --unchanged-group-format='' "$DMESG" - > "$LOG" || true
>> +dmesg | comm -13 "$DMESG" - > "$LOG" || true
>>   
>>   cat "$LOG"
>>   # Check for expected output
>> -- 
>> 2.25.1
>>
>>
>> -- 
>> Kees Cook
> 

Hi Kees,

You may want to consider a similar follow up to the one Miroslav made to 
the livepatching equivalent:

https://lore.kernel.org/live-patching/nycvar.YFH.7.76.2008271528000.27422@cbobk.fhfr.pm/T/#m1c17812d2c005dd57e9a299a4a492026a156619e

basically 'comm' will complain if two lines from dmesg have the same 
timestamp prefix and their text portions are not sorted.

Regards,

-- Joe