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Date:   Wed, 3 Feb 2021 15:48:25 +0100
From:   Marco Elver <elver@google.com>
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will.deacon@arm.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 06/12] kasan: rework krealloc tests
Message-ID: <YBq3uZOKeRnW3eBl@elver.google.com>
References: <cover.1612208222.git.andreyknvl@google.com>
 <995edb531f4f976277d7da9ca8a78a96a2ea356e.1612208222.git.andreyknvl@google.com>
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On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> This patch reworks KASAN-KUnit tests for krealloc() to:
> 
> 1. Check both slab and page_alloc based krealloc() implementations.
> 2. Allow at least one full granule to fit between old and new sizes for
>    each KASAN mode, and check accesses to that granule accordingly.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

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

> ---
>  lib/test_kasan.c | 91 ++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 81 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 5699e43ca01b..2bb52853f341 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -258,11 +258,14 @@ static void kmalloc_large_oob_right(struct kunit *test)
>  	kfree(ptr);
>  }
>  
> -static void kmalloc_oob_krealloc_more(struct kunit *test)
> +static void krealloc_more_oob_helper(struct kunit *test,
> +					size_t size1, size_t size2)
>  {
>  	char *ptr1, *ptr2;
> -	size_t size1 = 17;
> -	size_t size2 = 19;
> +	size_t middle;
> +
> +	KUNIT_ASSERT_LT(test, size1, size2);
> +	middle = size1 + (size2 - size1) / 2;
>  
>  	ptr1 = kmalloc(size1, GFP_KERNEL);
>  	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
> @@ -270,15 +273,31 @@ static void kmalloc_oob_krealloc_more(struct kunit *test)
>  	ptr2 = krealloc(ptr1, size2, GFP_KERNEL);
>  	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
>  
> -	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2 + OOB_TAG_OFF] = 'x');
> +	/* All offsets up to size2 must be accessible. */
> +	ptr2[size1 - 1] = 'x';
> +	ptr2[size1] = 'x';
> +	ptr2[middle] = 'x';
> +	ptr2[size2 - 1] = 'x';
> +
> +	/* Generic mode is precise, so unaligned size2 must be inaccessible. */
> +	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +		KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2] = 'x');
> +
> +	/* For all modes first aligned offset after size2 must be inaccessible. */
> +	KUNIT_EXPECT_KASAN_FAIL(test,
> +		ptr2[round_up(size2, KASAN_GRANULE_SIZE)] = 'x');
> +
>  	kfree(ptr2);
>  }
>  
> -static void kmalloc_oob_krealloc_less(struct kunit *test)
> +static void krealloc_less_oob_helper(struct kunit *test,
> +					size_t size1, size_t size2)
>  {
>  	char *ptr1, *ptr2;
> -	size_t size1 = 17;
> -	size_t size2 = 15;
> +	size_t middle;
> +
> +	KUNIT_ASSERT_LT(test, size2, size1);
> +	middle = size2 + (size1 - size2) / 2;
>  
>  	ptr1 = kmalloc(size1, GFP_KERNEL);
>  	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr1);
> @@ -286,10 +305,60 @@ static void kmalloc_oob_krealloc_less(struct kunit *test)
>  	ptr2 = krealloc(ptr1, size2, GFP_KERNEL);
>  	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
>  
> -	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2 + OOB_TAG_OFF] = 'x');
> +	/* Must be accessible for all modes. */
> +	ptr2[size2 - 1] = 'x';
> +
> +	/* Generic mode is precise, so unaligned size2 must be inaccessible. */
> +	if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +		KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size2] = 'x');
> +
> +	/* For all modes first aligned offset after size2 must be inaccessible. */
> +	KUNIT_EXPECT_KASAN_FAIL(test,
> +		ptr2[round_up(size2, KASAN_GRANULE_SIZE)] = 'x');
> +
> +	/*
> +	 * For all modes both middle and size1 should land in separate granules

middle, size1, and size2?

> +	 * and thus be inaccessible.
> +	 */
> +	KUNIT_EXPECT_LE(test, round_up(size2, KASAN_GRANULE_SIZE),
> +				round_down(middle, KASAN_GRANULE_SIZE));
> +	KUNIT_EXPECT_LE(test, round_up(middle, KASAN_GRANULE_SIZE),
> +				round_down(size1, KASAN_GRANULE_SIZE));
> +	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[middle] = 'x');
> +	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size1 - 1] = 'x');
> +	KUNIT_EXPECT_KASAN_FAIL(test, ptr2[size1] = 'x');
> +
>  	kfree(ptr2);
>  }
>  
> +static void krealloc_more_oob(struct kunit *test)
> +{
> +	krealloc_more_oob_helper(test, 201, 235);
> +}
> +
> +static void krealloc_less_oob(struct kunit *test)
> +{
> +	krealloc_less_oob_helper(test, 235, 201);
> +}
> +
> +static void krealloc_pagealloc_more_oob(struct kunit *test)
> +{
> +	/* page_alloc fallback in only implemented for SLUB. */
> +	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_SLUB);
> +
> +	krealloc_more_oob_helper(test, KMALLOC_MAX_CACHE_SIZE + 201,
> +					KMALLOC_MAX_CACHE_SIZE + 235);
> +}
> +
> +static void krealloc_pagealloc_less_oob(struct kunit *test)
> +{
> +	/* page_alloc fallback in only implemented for SLUB. */
> +	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_SLUB);
> +
> +	krealloc_less_oob_helper(test, KMALLOC_MAX_CACHE_SIZE + 235,
> +					KMALLOC_MAX_CACHE_SIZE + 201);
> +}
> +
>  static void kmalloc_oob_16(struct kunit *test)
>  {
>  	struct {
> @@ -983,8 +1052,10 @@ static struct kunit_case kasan_kunit_test_cases[] = {
>  	KUNIT_CASE(pagealloc_oob_right),
>  	KUNIT_CASE(pagealloc_uaf),
>  	KUNIT_CASE(kmalloc_large_oob_right),
> -	KUNIT_CASE(kmalloc_oob_krealloc_more),
> -	KUNIT_CASE(kmalloc_oob_krealloc_less),
> +	KUNIT_CASE(krealloc_more_oob),
> +	KUNIT_CASE(krealloc_less_oob),
> +	KUNIT_CASE(krealloc_pagealloc_more_oob),
> +	KUNIT_CASE(krealloc_pagealloc_less_oob),
>  	KUNIT_CASE(kmalloc_oob_16),
>  	KUNIT_CASE(kmalloc_uaf_16),
>  	KUNIT_CASE(kmalloc_oob_in_memset),
> -- 
> 2.30.0.365.g02bc693789-goog
>