linux-hardening - Re: [PATCH] kunit: memcpy: Split slow memcpy tests into MEMCPY_SLOW_KUNIT

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Message-ID: <ae952aa5-f113-8786-6fe4-60e5fa0ced2b@suse.cz>
Date:   Tue, 10 Jan 2023 08:51:01 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>,
        linux-hardening@...r.kernel.org, David Gow <davidgow@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Isabella Basso <isabbasso@...eup.net>,
        Dan Williams <dan.j.williams@...el.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org,
        Brendan Higgins <brendanhiggins@...gle.com>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        KUnit Development <kunit-dev@...glegroups.com>
Subject: Re: [PATCH] kunit: memcpy: Split slow memcpy tests into
 MEMCPY_SLOW_KUNIT_TEST

+Cc rest of kunit from MAINTAINERS

On 1/7/23 11:55, Geert Uytterhoeven wrote:
> Hi Kees,
> 
> On Sat, Jan 7, 2023 at 5:02 AM Kees Cook <keescook@...omium.org> wrote:
>> Since the long memcpy tests may stall a system for tens of seconds
>> in virtualized architecture environments, split those tests off under
>> CONFIG_MEMCPY_SLOW_KUNIT_TEST so they can be separately disabled.
>>
>> Reported-by: Guenter Roeck <linux@...ck-us.net>
>> Link: https://lore.kernel.org/lkml/20221226195206.GA2626419@roeck-us.net
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Nathan Chancellor <nathan@...nel.org>
>> Cc: linux-hardening@...r.kernel.org
>> Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> Thanks for your patch!
> 
>> --- a/lib/Kconfig.debug
>> +++ b/lib/Kconfig.debug
>> @@ -2621,6 +2621,15 @@ config MEMCPY_KUNIT_TEST
>>
>>           If unsure, say N.
>>
>> +config MEMCPY_SLOW_KUNIT_TEST
>> +       tristate "Include exhaustive memcpy tests" if !KUNIT_ALL_TESTS
> 
> Why the tristate?
> 
>> +       depends on MEMCPY_KUNIT_TEST
>> +       default KUNIT_ALL_TESTS
>> +       help
>> +         Some memcpy tests are quite exhaustive in checking for overlaps
>> +         and bit ranges. These can be very slow, so they are split out
>> +         as a separate config.
>> +
>>  config IS_SIGNED_TYPE_KUNIT_TEST
>>         tristate "Test is_signed_type() macro" if !KUNIT_ALL_TESTS
>>         depends on KUNIT
>> diff --git a/lib/memcpy_kunit.c b/lib/memcpy_kunit.c
>> index 89128551448d..cc1f36335a9b 100644
>> --- a/lib/memcpy_kunit.c
>> +++ b/lib/memcpy_kunit.c
>> @@ -307,8 +307,12 @@ static void set_random_nonzero(struct kunit *test, u8 *byte)
>>         }
>>  }
>>
>> -static void init_large(struct kunit *test)
>> +static int init_large(struct kunit *test)
>>  {
>> +       if (!IS_ENABLED(CONFIG_MEMCPY_SLOW_KUNIT_TEST)) {
>> +               kunit_skip(test, "Slow test skipped. Enable with CONFIG_MEMCPY_SLOW_KUNIT_TEST=y");
> 
> So I can't make the slower tests available for when I need them,
> but not run them by default?

Indeed it seems weird to tie this to a config option without runtime override.

> I guess that's why you made MEMCPY_SLOW_KUNIT_TEST tristate originally,
> to have a separate module with the slow tests?

On the other hand I can imagine requiring a separate module for slow tests
would lead to more churn - IIUC there would need to be two files instead of
memcpy_kunit.c, possibly a duplicated boilerplate code (or another shared .c
file).

So the idea is to have a generic way to mark some tests as slow and a way to
opt-in/opt-out for those when running the tests. Maybe KUnit folks already
have such mechanism or have an idea how to implement that.

>> +               return -EBUSY;
>> +       }
>>
>>         /* Get many bit patterns. */
>>         get_random_bytes(large_src, ARRAY_SIZE(large_src));
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds