linux-kernel - Re: [PATCH mm 2/3] kasan: migrate kasan_rcu

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Date:   Tue, 27 Sep 2022 15:16:20 +0200
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH mm 2/3] kasan: migrate kasan_rcu_uaf test to kunit

On Sat, Sep 24, 2022 at 08:31PM +0200, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Migrate the kasan_rcu_uaf test to the KUnit framework.
> 
> Changes to the implementation of the test:
> 
> - Call rcu_barrier() after call_rcu() to make that the RCU callbacks get
>   triggered before the test is over.
> 
> - Cast pointer passed to rcu_dereference_protected as __rcu to get rid of
>   the Sparse warning.
> 
> - Check that KASAN prints a report via KUNIT_EXPECT_KASAN_FAIL.
> 
> Initially, this test was intended to check that Generic KASAN prints
> auxiliary stack traces for RCU objects. Nevertheless, the test is enabled
> for all modes to make that KASAN reports bad accesses in RCU callbacks.
> 
> The presence of auxiliary stack traces for the Generic mode needs to be
> inspected manually.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

Reviewed-by: Marco Elver <elver@...gle.com>

> ---
>  mm/kasan/kasan_test.c        | 37 ++++++++++++++++++++++++++++++++++++
>  mm/kasan/kasan_test_module.c | 30 -----------------------------
>  2 files changed, 37 insertions(+), 30 deletions(-)
> 
> diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
> index 3a2886f85e69..005776325e20 100644
> --- a/mm/kasan/kasan_test.c
> +++ b/mm/kasan/kasan_test.c
> @@ -1134,6 +1134,42 @@ static void kmalloc_double_kzfree(struct kunit *test)
>  	KUNIT_EXPECT_KASAN_FAIL(test, kfree_sensitive(ptr));
>  }
>  
> +static struct kasan_rcu_info {
> +	int i;
> +	struct rcu_head rcu;
> +} *global_rcu_ptr;
> +
> +static void rcu_uaf_reclaim(struct rcu_head *rp)
> +{
> +	struct kasan_rcu_info *fp =
> +		container_of(rp, struct kasan_rcu_info, rcu);
> +
> +	kfree(fp);
> +	((volatile struct kasan_rcu_info *)fp)->i;
> +}
> +
> +/*
> + * Check that Generic KASAN prints auxiliary stack traces for RCU callbacks.
> + * The report needs to be inspected manually.
> + *
> + * This test is still enabled for other KASAN modes to make sure that all modes
> + * report bad accesses in tested scenarios.
> + */
> +static void rcu_uaf(struct kunit *test)
> +{
> +	struct kasan_rcu_info *ptr;
> +
> +	ptr = kmalloc(sizeof(struct kasan_rcu_info), GFP_KERNEL);
> +	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> +
> +	global_rcu_ptr = rcu_dereference_protected(
> +				(struct kasan_rcu_info __rcu *)ptr, NULL);
> +
> +	KUNIT_EXPECT_KASAN_FAIL(test,
> +		call_rcu(&global_rcu_ptr->rcu, rcu_uaf_reclaim);
> +		rcu_barrier());
> +}
> +
>  static void vmalloc_helpers_tags(struct kunit *test)
>  {
>  	void *ptr;
> @@ -1465,6 +1501,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
>  	KUNIT_CASE(kasan_bitops_generic),
>  	KUNIT_CASE(kasan_bitops_tags),
>  	KUNIT_CASE(kmalloc_double_kzfree),
> +	KUNIT_CASE(rcu_uaf),
>  	KUNIT_CASE(vmalloc_helpers_tags),
>  	KUNIT_CASE(vmalloc_oob),
>  	KUNIT_CASE(vmap_tags),
> diff --git a/mm/kasan/kasan_test_module.c b/mm/kasan/kasan_test_module.c
> index e4ca82dc2c16..4688cbcd722d 100644
> --- a/mm/kasan/kasan_test_module.c
> +++ b/mm/kasan/kasan_test_module.c
> @@ -62,35 +62,6 @@ static noinline void __init copy_user_test(void)
>  	kfree(kmem);
>  }
>  
> -static struct kasan_rcu_info {
> -	int i;
> -	struct rcu_head rcu;
> -} *global_rcu_ptr;
> -
> -static noinline void __init kasan_rcu_reclaim(struct rcu_head *rp)
> -{
> -	struct kasan_rcu_info *fp = container_of(rp,
> -						struct kasan_rcu_info, rcu);
> -
> -	kfree(fp);
> -	((volatile struct kasan_rcu_info *)fp)->i;
> -}
> -
> -static noinline void __init kasan_rcu_uaf(void)
> -{
> -	struct kasan_rcu_info *ptr;
> -
> -	pr_info("use-after-free in kasan_rcu_reclaim\n");
> -	ptr = kmalloc(sizeof(struct kasan_rcu_info), GFP_KERNEL);
> -	if (!ptr) {
> -		pr_err("Allocation failed\n");
> -		return;
> -	}
> -
> -	global_rcu_ptr = rcu_dereference_protected(ptr, NULL);
> -	call_rcu(&global_rcu_ptr->rcu, kasan_rcu_reclaim);
> -}
> -
>  static noinline void __init kasan_workqueue_work(struct work_struct *work)
>  {
>  	kfree(work);
> @@ -130,7 +101,6 @@ static int __init test_kasan_module_init(void)
>  	bool multishot = kasan_save_enable_multi_shot();
>  
>  	copy_user_test();
> -	kasan_rcu_uaf();
>  	kasan_workqueue_uaf();
>  
>  	kasan_restore_multi_shot(multishot);
> -- 
> 2.25.1