2021-01-05 18:31:20

by Andrey Konovalov

Subject: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

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 <[email protected]>
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);
KUNIT_ASSERT_NOT_ERR_OR_NULL(test, bits);

- /* Do the accesses past the 16 allocated bytes. */
- kasan_bitops_modify(test, BITS_PER_LONG, &bits[1]);
- kasan_bitops_test_and_modify(test, BITS_PER_LONG + BITS_PER_BYTE, &bits[1]);
+ /* Do the accesses past the 48 allocated bytes, but within the redone. */
+ kasan_bitops_modify(test, BITS_PER_LONG, (void *)bits + 48);
+ kasan_bitops_test_and_modify(test, BITS_PER_LONG + BITS_PER_BYTE, (void *)bits + 48);

kfree(bits);
}
--
2.29.2.729.g45daf8777d-goog

2021-01-12 13:57:53

by Marco Elver

Subject: Re: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

On Tue, Jan 05, 2021 at 07:27PM +0100, Andrey Konovalov 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 <[email protected]>
> Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a

Reviewed-by: Marco Elver <[email protected]>

> ---
> 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);
> KUNIT_ASSERT_NOT_ERR_OR_NULL(test, bits);
>
> - /* Do the accesses past the 16 allocated bytes. */
> - kasan_bitops_modify(test, BITS_PER_LONG, &bits[1]);
> - kasan_bitops_test_and_modify(test, BITS_PER_LONG + BITS_PER_BYTE, &bits[1]);
> + /* Do the accesses past the 48 allocated bytes, but within the redone. */
> + kasan_bitops_modify(test, BITS_PER_LONG, (void *)bits + 48);
> + kasan_bitops_test_and_modify(test, BITS_PER_LONG + BITS_PER_BYTE, (void *)bits + 48);
>
> kfree(bits);
> }
> --
> 2.29.2.729.g45daf8777d-goog
>

2021-01-12 23:19:56

by Alexander Potapenko

Subject: Re: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov <[email protected]> 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 <[email protected]>
> 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.

2021-01-13 02:32:40

by Andrey Konovalov

Subject: Re: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

On Tue, Jan 12, 2021 at 9:30 AM Alexander Potapenko <[email protected]> wrote:
>
> On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov <[email protected]> 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 <[email protected]>
> > 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!

2021-01-13 12:32:22

by Alexander Potapenko

Subject: Re: [PATCH 09/11] kasan: fix memory corruption in kasan_bitops_tags test

On Tue, Jan 12, 2021 at 9:07 PM 'Andrey Konovalov' via kasan-dev
<[email protected]> wrote:
>
> On Tue, Jan 12, 2021 at 9:30 AM Alexander Potapenko <[email protected]> wrote:
> >
> > On Tue, Jan 5, 2021 at 7:28 PM Andrey Konovalov <[email protected]> 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 <[email protected]>
> > > Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a
Reviewed-by: Alexander Potapenko <[email protected]>

> > > ---
> > > 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.

Ah, that's right.

> 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.

Agreed.