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Date:   Tue, 12 Jan 2021 14:55:18 +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>,
        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 09/11] kasan: fix memory corruption in kasan_bitops_tags
 test
Message-ID: <X/2qRlGsBj06ellk@elver.google.com>
References: <cover.1609871239.git.andreyknvl@google.com>
 <0c51a7266ea851797dc9816405fc40d860a48db1.1609871239.git.andreyknvl@google.com>
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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 <andreyknvl@google.com>
> Link: https://linux-review.googlesource.com/id/I67f51d1ee48f0a8d0fe2658c2a39e4879fe0832a

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

> ---
>  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
>