[PATCH] kasan: test: add globals left-out-of-bounds test

[Marco Elver]

Add a test checking that KASAN generic can also detect out-of-bounds
accesses to the left of globals.

Unfortunately it seems that GCC doesn't catch this (tested GCC 10, 11).
The main difference between GCC's globals redzoning and Clang's is that
GCC relies on using increased alignment to producing padding, where
Clang's redzoning implementation actually adds real data after the
global and doesn't rely on alignment to produce padding. I believe this
is the main reason why GCC can't reliably catch globals out-of-bounds in
this case.

Given this is now a known issue, to avoid failing the whole test suite,
skip this test case with GCC.

Reported-by: Kaiwan N Billimoria <kaiwan.b...@gmail.com>
Signed-off-by: Marco Elver <el...@google.com>
---
lib/test_kasan.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 67ed689a0b1b..69c32c91420b 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -700,7 +700,7 @@ static void kmem_cache_bulk(struct kunit *test)

static char global_array[10];

-static void kasan_global_oob(struct kunit *test)
+static void kasan_global_oob_right(struct kunit *test)
{
/*
* Deliberate out-of-bounds access. To prevent CONFIG_UBSAN_LOCAL_BOUNDS
@@ -723,6 +723,19 @@ static void kasan_global_oob(struct kunit *test)
KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
}

+static void kasan_global_oob_left(struct kunit *test)
+{
+ char *volatile array = global_array;
+ char *p = array - 3;
+
+ /*
+ * GCC is known to fail this test, skip it.
+ */
+ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_CC_IS_CLANG);
+ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
+ KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
+}
+
/* Check that ksize() makes the whole object accessible. */
static void ksize_unpoisons_memory(struct kunit *test)
{
@@ -1160,7 +1173,8 @@ static struct kunit_case kasan_kunit_test_cases[] = {
KUNIT_CASE(kmem_cache_oob),
KUNIT_CASE(kmem_cache_accounted),
KUNIT_CASE(kmem_cache_bulk),
- KUNIT_CASE(kasan_global_oob),
+ KUNIT_CASE(kasan_global_oob_right),
+ KUNIT_CASE(kasan_global_oob_left),
KUNIT_CASE(kasan_stack_oob),
KUNIT_CASE(kasan_alloca_oob_left),
KUNIT_CASE(kasan_alloca_oob_right),
--
2.34.0.rc2.393.gf8c9666880-goog

[Andrey Konovalov]

On Wed, Nov 17, 2021 at 12:09 PM Marco Elver <el...@google.com> wrote:
>
> Add a test checking that KASAN generic can also detect out-of-bounds
> accesses to the left of globals.
>
> Unfortunately it seems that GCC doesn't catch this (tested GCC 10, 11).
> The main difference between GCC's globals redzoning and Clang's is that
> GCC relies on using increased alignment to producing padding, where
> Clang's redzoning implementation actually adds real data after the
> global and doesn't rely on alignment to produce padding. I believe this
> is the main reason why GCC can't reliably catch globals out-of-bounds in
> this case.
>
> Given this is now a known issue, to avoid failing the whole test suite,
> skip this test case with GCC.
>
> Reported-by: Kaiwan N Billimoria <kaiwan.b...@gmail.com>
> Signed-off-by: Marco Elver <el...@google.com>

Hi Marco,

> ---
> lib/test_kasan.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 67ed689a0b1b..69c32c91420b 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -700,7 +700,7 @@ static void kmem_cache_bulk(struct kunit *test)
>
> static char global_array[10];
>
> -static void kasan_global_oob(struct kunit *test)
> +static void kasan_global_oob_right(struct kunit *test)
> {
> /*
> * Deliberate out-of-bounds access. To prevent CONFIG_UBSAN_LOCAL_BOUNDS
> @@ -723,6 +723,19 @@ static void kasan_global_oob(struct kunit *test)
> KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
> }
>
> +static void kasan_global_oob_left(struct kunit *test)
> +{
> + char *volatile array = global_array;
> + char *p = array - 3;
> +
> + /*
> + * GCC is known to fail this test, skip it.
> + */

Please link the KASAN bugzilla issue here.

> + KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_CC_IS_CLANG);
> + KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
> + KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
> +}
> +
> /* Check that ksize() makes the whole object accessible. */
> static void ksize_unpoisons_memory(struct kunit *test)
> {
> @@ -1160,7 +1173,8 @@ static struct kunit_case kasan_kunit_test_cases[] = {
> KUNIT_CASE(kmem_cache_oob),
> KUNIT_CASE(kmem_cache_accounted),
> KUNIT_CASE(kmem_cache_bulk),
> - KUNIT_CASE(kasan_global_oob),
> + KUNIT_CASE(kasan_global_oob_right),
> + KUNIT_CASE(kasan_global_oob_left),
> KUNIT_CASE(kasan_stack_oob),
> KUNIT_CASE(kasan_alloca_oob_left),
> KUNIT_CASE(kasan_alloca_oob_right),
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>

Otherwise:

Reviewed-by: Andrey Konovalov <andre...@gmail.com>

Thanks!

[Marco Elver]

I was wondering how to solve the cyclic dependency, because I wanted
to link this patch from the bugzilla.

Now that the bugzilla entry exists, I guess I can add it and then
update bugzilla with link to this patch closing the cycle. :-)

> > + KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_CC_IS_CLANG);
> > + KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
> > + KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
> > +}
> > +
> > /* Check that ksize() makes the whole object accessible. */
> > static void ksize_unpoisons_memory(struct kunit *test)
> > {
> > @@ -1160,7 +1173,8 @@ static struct kunit_case kasan_kunit_test_cases[] = {
> > KUNIT_CASE(kmem_cache_oob),
> > KUNIT_CASE(kmem_cache_accounted),
> > KUNIT_CASE(kmem_cache_bulk),
> > - KUNIT_CASE(kasan_global_oob),
> > + KUNIT_CASE(kasan_global_oob_right),
> > + KUNIT_CASE(kasan_global_oob_left),
> > KUNIT_CASE(kasan_stack_oob),
> > KUNIT_CASE(kasan_alloca_oob_left),
> > KUNIT_CASE(kasan_alloca_oob_right),
> > --
> > 2.34.0.rc2.393.gf8c9666880-goog
> >
>
> Otherwise:
>
> Reviewed-by: Andrey Konovalov <andre...@gmail.com>
>
> Thanks!
>

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[Marco Elver]

Add a test checking that KASAN generic can also detect out-of-bounds
accesses to the left of globals.

Unfortunately it seems that GCC doesn't catch this (tested GCC 10, 11).
The main difference between GCC's globals redzoning and Clang's is that
GCC relies on using increased alignment to producing padding, where
Clang's redzoning implementation actually adds real data after the
global and doesn't rely on alignment to produce padding. I believe this
is the main reason why GCC can't reliably catch globals out-of-bounds in
this case.

Given this is now a known issue, to avoid failing the whole test suite,
skip this test case with GCC.

Reported-by: Kaiwan N Billimoria <kaiwan.b...@gmail.com>
Signed-off-by: Marco Elver <el...@google.com>

Reviewed-by: Andrey Konovalov <andre...@gmail.com>
---
v2:
* Add bugzilla link.
---
lib/test_kasan.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 67ed689a0b1b..40f7274297c1 100644

--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -700,7 +700,7 @@ static void kmem_cache_bulk(struct kunit *test)

static char global_array[10];

-static void kasan_global_oob(struct kunit *test)
+static void kasan_global_oob_right(struct kunit *test)
{
/*
* Deliberate out-of-bounds access. To prevent CONFIG_UBSAN_LOCAL_BOUNDS

@@ -723,6 +723,20 @@ static void kasan_global_oob(struct kunit *test)

KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
}

+static void kasan_global_oob_left(struct kunit *test)
+{
+ char *volatile array = global_array;
+ char *p = array - 3;
+
+ /*
+ * GCC is known to fail this test, skip it.

+ * See https://bugzilla.kernel.org/show_bug.cgi?id=215051.
+ */

+ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_CC_IS_CLANG);
+ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
+ KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p);
+}
+
/* Check that ksize() makes the whole object accessible. */
static void ksize_unpoisons_memory(struct kunit *test)
{

@@ -1160,7 +1174,8 @@ static struct kunit_case kasan_kunit_test_cases[] = {