Date:   Wed, 4 May 2022 12:43:37 -0700
From:   Kees Cook <keescook@...omium.org>
To:     David Gow <davidgow@...gle.com>
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Subject: Re: [PATCH 03/32] flex_array: Add Kunit tests

On Wed, May 04, 2022 at 11:00:38AM +0800, David Gow wrote:
> On Wed, May 4, 2022 at 9:47 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > Add tests for the new flexible array structure helpers. These can be run
> > with:
> >
> >   make ARCH=um mrproper
> >   ./tools/testing/kunit/kunit.py config
> 
> Nit: it shouldn't be necessary to run kunit.py config separately:
> kunit.py run will configure the kernel if necessary.

Ah yes, I think you mentioned this before. I'll adjust the commit log.

> 
> >   ./tools/testing/kunit/kunit.py run flex_array
> >
> > Cc: David Gow <davidgow@...gle.com>
> > Cc: kunit-dev@...glegroups.com
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > ---
> 
> This looks pretty good to me: it certainly worked on the different
> setups I tried (um, x86_64, x86_64+KASAN).
> 
> A few minor nitpicks inline, mostly around minor config-y things, or
> things which weren't totally clear on my first read-through.
> 
> Hopefully one day, with the various stubbing features or something
> similar, we'll be able to check against allocation failures in
> flex_dup(), too, but otherwise nothing seems too obviously missing.
> 
> Reviewed-by: David Gow <davidgow@...gle.com>

Great; thanks for the review and testing!

> 
> -- David
> 
> >  lib/Kconfig.debug      |  12 +-
> >  lib/Makefile           |   1 +
> >  lib/flex_array_kunit.c | 523 +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 531 insertions(+), 5 deletions(-)
> >  create mode 100644 lib/flex_array_kunit.c
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 9077bb38bc93..8bae6b169c50 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -2551,11 +2551,6 @@ config OVERFLOW_KUNIT_TEST
> >           Builds unit tests for the check_*_overflow(), size_*(), allocation, and
> >           related functions.
> >
> > -         For more information on KUnit and unit tests in general please refer
> > -         to the KUnit documentation in Documentation/dev-tools/kunit/.
> > -
> > -         If unsure, say N.
> > -
> 
> Nit: while I'm not against removing some of this boilerplate, is it
> better suited for a separate commit?

Make sense, yes. I'll drop this for now.

> 
> >  config STACKINIT_KUNIT_TEST
> >         tristate "Test level of stack variable initialization" if !KUNIT_ALL_TESTS
> >         depends on KUNIT
> > @@ -2567,6 +2562,13 @@ config STACKINIT_KUNIT_TEST
> >           CONFIG_GCC_PLUGIN_STRUCTLEAK, CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF,
> >           or CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.
> >
> > +config FLEX_ARRAY_KUNIT_TEST
> > +       tristate "Test flex_*() family of helper functions at runtime" if !KUNIT_ALL_TESTS
> > +       depends on KUNIT
> > +       default KUNIT_ALL_TESTS
> > +       help
> > +         Builds unit tests for flexible array copy helper functions.
> > +
> 
> Nit: checkpatch warns that the description here may be insufficient:
> WARNING: please write a help paragraph that fully describes the config symbol

Yeah, I don't know anything to put here that isn't just more
boilerplate, so I'm choosing to ignore this for now. :)

> > [...]
> > +struct normal {
> > +       size_t  datalen;
> > +       u32     data[];
> > +};
> > +
> > +struct decl_normal {
> > +       DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(size_t, datalen);
> > +       DECLARE_FLEX_ARRAY_ELEMENTS(u32, data);
> > +};
> > +
> > +struct aligned {
> > +       unsigned short  datalen;
> > +       char            data[] __aligned(__alignof__(u64));
> > +};
> > +
> > +struct decl_aligned {
> > +       DECLARE_FLEX_ARRAY_ELEMENTS_COUNT(unsigned short, datalen);
> > +       DECLARE_FLEX_ARRAY_ELEMENTS(char, data) __aligned(__alignof__(u64));
> > +};
> > +
> > +static void struct_test(struct kunit *test)
> > +{
> > +       COMPARE_STRUCTS(struct normal, struct decl_normal);
> > +       COMPARE_STRUCTS(struct aligned, struct decl_aligned);
> > +}
> 
> If I understand it, the purpose of this is to ensure that structs both
> with and without the flexible array declaration have the same memory
> layout?
> 
> If so, any chance of a comment briefly stating that's the purpose (or
> renaming this test struct_layout_test())?

Yeah, good idea; I'll improve the naming.

> 
> Also, would it make sense to do the same with the struct with internal
> padding below?

Heh, yes, good point! :)

> [...]
> > +#define CHECK_COPY(ptr)                do {                                            \
> > +       typeof(*(ptr)) *_cc_dst = (ptr);                                        \
> > +       KUNIT_EXPECT_EQ(test, _cc_dst->induce_padding, 0);                      \
> > +       memcpy(&padding, &_cc_dst->induce_padding + sizeof(_cc_dst->induce_padding), \
> > +              sizeof(padding));                                                \
> > +       /* Padding should be zero too. */                                       \
> > +       KUNIT_EXPECT_EQ(test, padding, 0);                                      \
> > +       KUNIT_EXPECT_EQ(test, src->count, _cc_dst->count);                      \
> > +       KUNIT_EXPECT_EQ(test, _cc_dst->count, TEST_TARGET);                     \
> > +       for (i = 0; i < _cc_dst->count - 1; i++) {                              \
> > +               /* 'A' is 0x41, and here repeated in a u32. */                  \
> 
> Would it be simpler to just note that the magic value is 0x41, rather
> than have it be the character 'A'?

Yeah, now fixed.

> [...]
> > +       CHECK_COPY(&encap->fas);
> > +       /* Check that items external to "fas" are zero. */
> > +       KUNIT_EXPECT_EQ(test, encap->flags, 0);
> > +       KUNIT_EXPECT_EQ(test, encap->junk, 0);
> > +       kfree(encap);
> > +#undef MAGIC_WORD
> 
> MAGIC_WORD isn't defined (or used) for flux_dup_test? Is it worth
> using it (or something similar) for the 'A' / 0x14141414 and the
> CHECK_COPY() macro?

Oops, yes. Fixed.

Thanks again!

-Kees

-- 
Kees Cook

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