linux-kernel - Re: [PATCH] kunit: kasan_test: disable fortify string checker on kmalloc_oob

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Date:   Wed, 13 Dec 2023 14:42:15 -0700
From:   Nico Pache <npache@...hat.com>
To:     Andrey Konovalov <andreyknvl@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com, akpm@...ux-foundation.org,
        vincenzo.frascino@....com, dvyukov@...gle.com, glider@...gle.com,
        ryabinin.a.a@...il.com
Subject: Re: [PATCH] kunit: kasan_test: disable fortify string checker on kmalloc_oob_memset

On Wed, Dec 13, 2023 at 7:34 AM Andrey Konovalov <andreyknvl@...il.com> wrote:
>
> On Wed, Dec 13, 2023 at 12:27 AM Nico Pache <npache@...hat.com> wrote:
> >
> > similar to commit 09c6304e38e4 ("kasan: test: fix compatibility with
> > FORTIFY_SOURCE") the kernel is panicing in kmalloc_oob_memset_*.
> >
> > This is due to the `ptr` not being hidden from the optimizer which would
> > disable the runtime fortify string checker.
> >
> > kernel BUG at lib/string_helpers.c:1048!
> > Call Trace:
> > [<00000000272502e2>] fortify_panic+0x2a/0x30
> > ([<00000000272502de>] fortify_panic+0x26/0x30)
> > [<001bffff817045c4>] kmalloc_oob_memset_2+0x22c/0x230 [kasan_test]
> >
> > Hide the `ptr` variable from the optimizer to fix the kernel panic.
> > Also define a size2 variable and hide that as well. This cleans up
> > the code and follows the same convention as other tests.
> >
> > Signed-off-by: Nico Pache <npache@...hat.com>
> > ---
> >  mm/kasan/kasan_test.c | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
> > index 8281eb42464b..5aeba810ba70 100644
> > --- a/mm/kasan/kasan_test.c
> > +++ b/mm/kasan/kasan_test.c
> > @@ -493,14 +493,17 @@ static void kmalloc_oob_memset_2(struct kunit *test)
> >  {
> >         char *ptr;
> >         size_t size = 128 - KASAN_GRANULE_SIZE;
> > +       size_t size2 = 2;
>
> Let's name this variable access_size or memset_size. Here and in the
> other changed tests.

Hi Andrey,

I agree that is a better variable name, but I chose size2 because
other kasan tests follow the same pattern.

Please let me know if you still want me to update it given that info
and I'll send a V2.

Cheers,
-- Nico

>
> >         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
> >
> >         ptr = kmalloc(size, GFP_KERNEL);
> >         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > +       OPTIMIZER_HIDE_VAR(ptr);
> >         OPTIMIZER_HIDE_VAR(size);
> > -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, 2));
> > +       OPTIMIZER_HIDE_VAR(size2);
> > +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, size2));
> >         kfree(ptr);
> >  }
> >
> > @@ -508,14 +511,17 @@ static void kmalloc_oob_memset_4(struct kunit *test)
> >  {
> >         char *ptr;
> >         size_t size = 128 - KASAN_GRANULE_SIZE;
> > +       size_t size2 = 4;
> >
> >         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
> >
> >         ptr = kmalloc(size, GFP_KERNEL);
> >         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > +       OPTIMIZER_HIDE_VAR(ptr);
> >         OPTIMIZER_HIDE_VAR(size);
> > -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, 4));
> > +       OPTIMIZER_HIDE_VAR(size2);
> > +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, size2));
> >         kfree(ptr);
> >  }
> >
> > @@ -523,14 +529,17 @@ static void kmalloc_oob_memset_8(struct kunit *test)
> >  {
> >         char *ptr;
> >         size_t size = 128 - KASAN_GRANULE_SIZE;
> > +       size_t size2 = 8;
> >
> >         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
> >
> >         ptr = kmalloc(size, GFP_KERNEL);
> >         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > +       OPTIMIZER_HIDE_VAR(ptr);
> >         OPTIMIZER_HIDE_VAR(size);
> > -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, 8));
> > +       OPTIMIZER_HIDE_VAR(size2);
> > +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, size2));
> >         kfree(ptr);
> >  }
> >
> > @@ -538,14 +547,17 @@ static void kmalloc_oob_memset_16(struct kunit *test)
> >  {
> >         char *ptr;
> >         size_t size = 128 - KASAN_GRANULE_SIZE;
> > +       size_t size2 = 16;
> >
> >         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
> >
> >         ptr = kmalloc(size, GFP_KERNEL);
> >         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > +       OPTIMIZER_HIDE_VAR(ptr);
> >         OPTIMIZER_HIDE_VAR(size);
> > -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, 16));
> > +       OPTIMIZER_HIDE_VAR(size2);
> > +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, size2));
> >         kfree(ptr);
> >  }
> >
> > --
> > 2.43.0
> >
>
> With the fix mentioned above addressed:
>
> Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>
>