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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 12 Jan 2021 21:06:56 +0100
Message-ID: <CAAeHK+xbYpuipd3+Jew7=fL8Mn2J1ZzOVyzK+X6bvtLCeiGFuw@mail.gmail.com>
Subject: Re: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test
To:     Alexander Potapenko <glider@google.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will.deacon@arm.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Jan 12, 2021 at 9:30 AM Alexander Potapenko <glider@google.com> wrote:
>
> On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov <andreyknvl@google.com> wrote:
> >
> > Since the hardware tag-based KASAN mode might not have a redzone that
> > comes after an allocated object (when kasan.mode=prod is enabled), the
> > kasan_bitops_tags() test ends up corrupting the next object in memory.
> >
> > Change the test so it always accesses the redzone that lies within the
> > allocated object's boundaries.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> > Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a
> > ---
> >  lib/test_kasan.c | 12 ++++++------
> >  1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > index b67da7f6e17f..3ea52da52714 100644
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -771,17 +771,17 @@ static void kasan_bitops_tags(struct kunit *test)
> >
> >         /* This test is specifically crafted for the tag-based mode. */
> >         if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> > -               kunit_info(test, "skipping, CONFIG_KASAN_SW_TAGS required");
> > +               kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
> >                 return;
> >         }
> >
> > -       /* Allocation size will be rounded to up granule size, which is 16. */
> > -       bits = kzalloc(sizeof(*bits), GFP_KERNEL);
> > +       /* kmalloc-64 cache will be used and the last 16 bytes will be the redzone. */
> > +       bits = kzalloc(48, GFP_KERNEL);
>
> I think it might make sense to call ksize() here to ensure we have
> these spare bytes.

Calling ksize() will unpoison the whole object.

I think it's OK to make assumptions about KASAN internals in tests. I
would actually say that we need more tests that check such internal
properties.

Thanks!