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Date:   Tue, 12 Jan 2021 14:17:34 +0100
From:   Marco Elver <elver@...gle.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Will Deacon <will.deacon@....com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/11] kasan: add match-all tag tests

On Tue, Jan 05, 2021 at 07:27PM +0100, Andrey Konovalov wrote:
> Add 3 new tests for tag-based KASAN modes:
> 
> 1. Check that match-all pointer tag is not assigned randomly.
> 2. Check that 0xff works as a match-all pointer tag.
> 3. Check that there are no match-all memory tags.
> 
> Note, that test #3 causes a significant number (255) of KASAN reports
> to be printed during execution for the SW_TAGS mode.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> Link: https://linux-review.googlesource.com/id/I78f1375efafa162b37f3abcb2c5bc2f3955dfd8e
> ---
>  lib/test_kasan.c | 93 ++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/kasan/kasan.h |  6 ++++
>  2 files changed, 99 insertions(+)
> 
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 46e578c8e842..f1eda0bcc780 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -13,6 +13,7 @@
>  #include <linux/mman.h>
>  #include <linux/module.h>
>  #include <linux/printk.h>
> +#include <linux/random.h>
>  #include <linux/slab.h>
>  #include <linux/string.h>
>  #include <linux/uaccess.h>
> @@ -790,6 +791,95 @@ static void vmalloc_oob(struct kunit *test)
>  	vfree(area);
>  }
>  
> +/*
> + * Check that match-all pointer tag is not assigned randomly for
> + * tag-based modes.
> + */
> +static void match_all_not_assigned(struct kunit *test)
> +{
> +	char *ptr;
> +	struct page *pages;
> +	int i, size, order;
> +
> +	for (i = 0; i < 256; i++) {
> +		size = get_random_int() % KMALLOC_MAX_SIZE;

size appears to be unused?

> +		ptr = kmalloc(128, GFP_KERNEL);
> +		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> +		KUNIT_EXPECT_NE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
> +		kfree(ptr);
> +	}
> +
> +	for (i = 0; i < 256; i++) {
> +		order = get_random_int() % 4;
> +		pages = alloc_pages(GFP_KERNEL, order);
> +		ptr = page_address(pages);
> +		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> +		KUNIT_EXPECT_NE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
> +		free_pages((unsigned long)ptr, order);
> +	}
> +}
> +
> +/* Check that 0xff works as a match-all pointer tag for tag-based modes. */
> +static void match_all_ptr_tag(struct kunit *test)
> +{
> +	char *ptr;
> +	u8 tag;
> +
> +	if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> +		kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
> +		return;
> +	}
> +
> +	ptr = kmalloc(128, GFP_KERNEL);
> +	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> +
> +	/* Backup the assigned tag. */
> +	tag = get_tag(ptr);
> +	KUNIT_EXPECT_NE(test, tag, (u8)KASAN_TAG_KERNEL);
> +
> +	/* Reset the tag to 0xff.*/
> +	ptr = set_tag(ptr, KASAN_TAG_KERNEL);
> +
> +	/* This access shouldn't trigger a KASAN report. */
> +	*ptr = 0;
> +
> +	/* Recover the pointer tag and free. */
> +	ptr = set_tag(ptr, tag);
> +	kfree(ptr);
> +}
> +
> +/* Check that there are no match-all memory tags for tag-based modes. */
> +static void match_all_mem_tag(struct kunit *test)
> +{
> +	char *ptr;
> +	int tag;
> +
> +	if (IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> +		kunit_info(test, "skipping, CONFIG_KASAN_SW/HW_TAGS required");
> +		return;
> +	}
> +
> +	ptr = kmalloc(128, GFP_KERNEL);
> +	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> +	KUNIT_EXPECT_NE(test, (u8)get_tag(ptr), (u8)KASAN_TAG_KERNEL);
> +
> +	/* For each possible tag value not matching the pointer tag. */
> +	for (tag = KASAN_TAG_MIN; tag <= KASAN_TAG_KERNEL; tag++) {
> +		if (tag == get_tag(ptr))
> +			continue;
> +
> +		/* Mark the first memory granule with the chosen memory tag. */
> +		kasan_poison(ptr, KASAN_GRANULE_SIZE, (u8)tag);
> +
> +		/* This access must cause a KASAN report. */
> +		KUNIT_EXPECT_KASAN_FAIL(test, *ptr = 0);
> +	}
> +
> +	/* Recover the memory tag and free. */
> +	kasan_poison(ptr, KASAN_GRANULE_SIZE, get_tag(ptr));
> +	kfree(ptr);
> +}
> +
>  static struct kunit_case kasan_kunit_test_cases[] = {
>  	KUNIT_CASE(kmalloc_oob_right),
>  	KUNIT_CASE(kmalloc_oob_left),
> @@ -829,6 +919,9 @@ static struct kunit_case kasan_kunit_test_cases[] = {
>  	KUNIT_CASE(kasan_bitops_tags),
>  	KUNIT_CASE(kmalloc_double_kzfree),
>  	KUNIT_CASE(vmalloc_oob),
> +	KUNIT_CASE(match_all_not_assigned),
> +	KUNIT_CASE(match_all_ptr_tag),
> +	KUNIT_CASE(match_all_mem_tag),
>  	{}
>  };
>  
> diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> index 3b38baddec47..c3fb9bf241d3 100644
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -36,6 +36,12 @@ extern bool kasan_flag_panic __ro_after_init;
>  #define KASAN_TAG_INVALID	0xFE /* inaccessible memory tag */
>  #define KASAN_TAG_MAX		0xFD /* maximum value for random tags */
>  
> +#ifdef CONFIG_KASAN_HW_TAGS
> +#define KASAN_TAG_MIN		0xF0 /* mimimum value for random tags */
> +#else
> +#define KASAN_TAG_MIN		0x00 /* mimimum value for random tags */
> +#endif
> +
>  #ifdef CONFIG_KASAN_GENERIC
>  #define KASAN_FREE_PAGE         0xFF  /* page was freed */
>  #define KASAN_PAGE_REDZONE      0xFE  /* redzone for kmalloc_large allocations */
> -- 
> 2.29.2.729.g45daf8777d-goog
> 

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