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Date:   Tue, 12 Jan 2021 14:07:19 +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 03/11] kasan: clean up comments in tests

On Tue, Jan 05, 2021 at 07:27PM +0100, Andrey Konovalov wrote:
> Clarify and update comments and info messages in KASAN tests.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> Link: https://linux-review.googlesource.com/id/I6c816c51fa1e0eb7aa3dead6bda1f339d2af46c8

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

> ---
>  lib/test_kasan.c        | 94 +++++++++++++++++++++++------------------
>  lib/test_kasan_module.c |  5 ++-
>  2 files changed, 55 insertions(+), 44 deletions(-)
> 
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 2947274cc2d3..46e578c8e842 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -28,10 +28,9 @@
>  #define OOB_TAG_OFF (IS_ENABLED(CONFIG_KASAN_GENERIC) ? 0 : KASAN_GRANULE_SIZE)
>  
>  /*
> - * We assign some test results to these globals to make sure the tests
> - * are not eliminated as dead code.
> + * Some tests use these global variables to store return values from function
> + * calls that could otherwise be eliminated by the compiler as dead code.
>   */
> -
>  void *kasan_ptr_result;
>  int kasan_int_result;
>  
> @@ -39,14 +38,13 @@ static struct kunit_resource resource;
>  static struct kunit_kasan_expectation fail_data;
>  static bool multishot;
>  
> +/*
> + * Temporarily enable multi-shot mode. Otherwise, KASAN would only report the
> + * first detected bug and panic the kernel if panic_on_warn is enabled.
> + */
>  static int kasan_test_init(struct kunit *test)
>  {
> -	/*
> -	 * Temporarily enable multi-shot mode and set panic_on_warn=0.
> -	 * Otherwise, we'd only get a report for the first case.
> -	 */
>  	multishot = kasan_save_enable_multi_shot();
> -
>  	return 0;
>  }
>  
> @@ -56,12 +54,12 @@ static void kasan_test_exit(struct kunit *test)
>  }
>  
>  /**
> - * KUNIT_EXPECT_KASAN_FAIL() - Causes a test failure when the expression does
> - * not cause a KASAN error. This uses a KUnit resource named "kasan_data." Do
> - * Do not use this name for a KUnit resource outside here.
> - *
> + * KUNIT_EXPECT_KASAN_FAIL() - check that the executed expression produces a
> + * KASAN report; causes a test failure otherwise. This relies on a KUnit
> + * resource named "kasan_data". Do not use this name for KUnit resources
> + * outside of KASAN tests.
>   */
> -#define KUNIT_EXPECT_KASAN_FAIL(test, condition) do { \
> +#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
>  	fail_data.report_expected = true; \
>  	fail_data.report_found = false; \
>  	kunit_add_named_resource(test, \
> @@ -69,7 +67,7 @@ static void kasan_test_exit(struct kunit *test)
>  				NULL, \
>  				&resource, \
>  				"kasan_data", &fail_data); \
> -	condition; \
> +	expression; \
>  	KUNIT_EXPECT_EQ(test, \
>  			fail_data.report_expected, \
>  			fail_data.report_found); \
> @@ -117,11 +115,12 @@ static void kmalloc_pagealloc_oob_right(struct kunit *test)
>  	size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
>  
>  	if (!IS_ENABLED(CONFIG_SLUB)) {
> -		kunit_info(test, "CONFIG_SLUB is not enabled.");
> +		kunit_info(test, "skipping, CONFIG_SLUB required");
>  		return;
>  	}
>  
> -	/* Allocate a chunk that does not fit into a SLUB cache to trigger
> +	/*
> +	 * Allocate a chunk that does not fit into a SLUB cache to trigger
>  	 * the page allocator fallback.
>  	 */
>  	ptr = kmalloc(size, GFP_KERNEL);
> @@ -137,7 +136,7 @@ static void kmalloc_pagealloc_uaf(struct kunit *test)
>  	size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
>  
>  	if (!IS_ENABLED(CONFIG_SLUB)) {
> -		kunit_info(test, "CONFIG_SLUB is not enabled.");
> +		kunit_info(test, "skipping, CONFIG_SLUB required");
>  		return;
>  	}
>  
> @@ -154,7 +153,7 @@ static void kmalloc_pagealloc_invalid_free(struct kunit *test)
>  	size_t size = KMALLOC_MAX_CACHE_SIZE + 10;
>  
>  	if (!IS_ENABLED(CONFIG_SLUB)) {
> -		kunit_info(test, "CONFIG_SLUB is not enabled.");
> +		kunit_info(test, "skipping, CONFIG_SLUB required");
>  		return;
>  	}
>  
> @@ -168,7 +167,9 @@ static void kmalloc_large_oob_right(struct kunit *test)
>  {
>  	char *ptr;
>  	size_t size = KMALLOC_MAX_CACHE_SIZE - 256;
> -	/* Allocate a chunk that is large enough, but still fits into a slab
> +
> +	/*
> +	 * Allocate a chunk that is large enough, but still fits into a slab
>  	 * and does not trigger the page allocator fallback in SLUB.
>  	 */
>  	ptr = kmalloc(size, GFP_KERNEL);
> @@ -218,7 +219,7 @@ static void kmalloc_oob_16(struct kunit *test)
>  
>  	/* This test is specifically crafted for the generic mode. */
>  	if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> -		kunit_info(test, "CONFIG_KASAN_GENERIC required\n");
> +		kunit_info(test, "skipping, CONFIG_KASAN_GENERIC required");
>  		return;
>  	}
>  
> @@ -454,7 +455,7 @@ static void kasan_global_oob(struct kunit *test)
>  
>  	/* Only generic mode instruments globals. */
>  	if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> -		kunit_info(test, "CONFIG_KASAN_GENERIC required");
> +		kunit_info(test, "skipping, CONFIG_KASAN_GENERIC required");
>  		return;
>  	}
>  
> @@ -469,10 +470,13 @@ static void ksize_unpoisons_memory(struct kunit *test)
>  	ptr = kmalloc(size, GFP_KERNEL);
>  	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>  	real_size = ksize(ptr);
> -	/* This access doesn't trigger an error. */
> +
> +	/* This access shouldn't trigger a KASAN report. */
>  	ptr[size] = 'x';
> -	/* This one does. */
> +
> +	/* This one must. */
>  	KUNIT_EXPECT_KASAN_FAIL(test, ptr[real_size] = 'y');
> +
>  	kfree(ptr);
>  }
>  
> @@ -483,7 +487,7 @@ static void kasan_stack_oob(struct kunit *test)
>  	char *p = &stack_array[ARRAY_SIZE(stack_array) + i];
>  
>  	if (!IS_ENABLED(CONFIG_KASAN_STACK)) {
> -		kunit_info(test, "CONFIG_KASAN_STACK is not enabled");
> +		kunit_info(test, "skipping, CONFIG_KASAN_STACK required");
>  		return;
>  	}
>  
> @@ -498,12 +502,12 @@ static void kasan_alloca_oob_left(struct kunit *test)
>  
>  	/* Only generic mode instruments dynamic allocas. */
>  	if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> -		kunit_info(test, "CONFIG_KASAN_GENERIC required");
> +		kunit_info(test, "skipping, CONFIG_KASAN_GENERIC required");
>  		return;
>  	}
>  
>  	if (!IS_ENABLED(CONFIG_KASAN_STACK)) {
> -		kunit_info(test, "CONFIG_KASAN_STACK is not enabled");
> +		kunit_info(test, "skipping, CONFIG_KASAN_STACK required");
>  		return;
>  	}
>  
> @@ -518,12 +522,12 @@ static void kasan_alloca_oob_right(struct kunit *test)
>  
>  	/* Only generic mode instruments dynamic allocas. */
>  	if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> -		kunit_info(test, "CONFIG_KASAN_GENERIC required");
> +		kunit_info(test, "skipping, CONFIG_KASAN_GENERIC required");
>  		return;
>  	}
>  
>  	if (!IS_ENABLED(CONFIG_KASAN_STACK)) {
> -		kunit_info(test, "CONFIG_KASAN_STACK is not enabled");
> +		kunit_info(test, "skipping, CONFIG_KASAN_STACK required");
>  		return;
>  	}
>  
> @@ -568,7 +572,7 @@ static void kmem_cache_invalid_free(struct kunit *test)
>  		return;
>  	}
>  
> -	/* Trigger invalid free, the object doesn't get freed */
> +	/* Trigger invalid free, the object doesn't get freed. */
>  	KUNIT_EXPECT_KASAN_FAIL(test, kmem_cache_free(cache, p + 1));
>  
>  	/*
> @@ -585,10 +589,12 @@ static void kasan_memchr(struct kunit *test)
>  	char *ptr;
>  	size_t size = 24;
>  
> -	/* See https://bugzilla.kernel.org/show_bug.cgi?id=206337 */
> +	/*
> +	 * str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT.
> +	 * See https://bugzilla.kernel.org/show_bug.cgi?id=206337 for details.
> +	 */
>  	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
> -		kunit_info(test,
> -			"str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT");
> +		kunit_info(test, "skipping, CONFIG_AMD_MEM_ENCRYPT enabled");
>  		return;
>  	}
>  
> @@ -610,10 +616,12 @@ static void kasan_memcmp(struct kunit *test)
>  	size_t size = 24;
>  	int arr[9];
>  
> -	/* See https://bugzilla.kernel.org/show_bug.cgi?id=206337 */
> +	/*
> +	 * str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT.
> +	 * See https://bugzilla.kernel.org/show_bug.cgi?id=206337 for details.
> +	 */
>  	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
> -		kunit_info(test,
> -			"str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT");
> +		kunit_info(test, "skipping, CONFIG_AMD_MEM_ENCRYPT enabled");
>  		return;
>  	}
>  
> @@ -634,10 +642,12 @@ static void kasan_strings(struct kunit *test)
>  	char *ptr;
>  	size_t size = 24;
>  
> -	/* See https://bugzilla.kernel.org/show_bug.cgi?id=206337 */
> +	/*
> +	 * str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT.
> +	 * See https://bugzilla.kernel.org/show_bug.cgi?id=206337 for details.
> +	 */
>  	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
> -		kunit_info(test,
> -			"str* functions are not instrumented with CONFIG_AMD_MEM_ENCRYPT");
> +		kunit_info(test, "skipping, CONFIG_AMD_MEM_ENCRYPT enabled");
>  		return;
>  	}
>  
> @@ -701,12 +711,12 @@ static void kasan_bitops_generic(struct kunit *test)
>  
>  	/* This test is specifically crafted for the generic mode. */
>  	if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) {
> -		kunit_info(test, "CONFIG_KASAN_GENERIC required\n");
> +		kunit_info(test, "skipping, CONFIG_KASAN_GENERIC required");
>  		return;
>  	}
>  
>  	/*
> -	 * Allocate 1 more byte, which causes kzalloc to round up to 16-bytes;
> +	 * Allocate 1 more byte, which causes kzalloc to round up to 16 bytes;
>  	 * this way we do not actually corrupt other memory.
>  	 */
>  	bits = kzalloc(sizeof(*bits) + 1, GFP_KERNEL);
> @@ -733,7 +743,7 @@ 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, "CONFIG_KASAN_SW_TAGS required\n");
> +		kunit_info(test, "skipping, CONFIG_KASAN_SW_TAGS required");
>  		return;
>  	}
>  
> @@ -765,7 +775,7 @@ static void vmalloc_oob(struct kunit *test)
>  	void *area;
>  
>  	if (!IS_ENABLED(CONFIG_KASAN_VMALLOC)) {
> -		kunit_info(test, "CONFIG_KASAN_VMALLOC is not enabled.");
> +		kunit_info(test, "skipping, CONFIG_KASAN_VMALLOC required");
>  		return;
>  	}
>  
> diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
> index 3b4cc77992d2..eee017ff8980 100644
> --- a/lib/test_kasan_module.c
> +++ b/lib/test_kasan_module.c
> @@ -123,8 +123,9 @@ static noinline void __init kasan_workqueue_uaf(void)
>  static int __init test_kasan_module_init(void)
>  {
>  	/*
> -	 * Temporarily enable multi-shot mode. Otherwise, we'd only get a
> -	 * report for the first case.
> +	 * Temporarily enable multi-shot mode. Otherwise, KASAN would only
> +	 * report the first detected bug and panic the kernel if panic_on_warn
> +	 * is enabled.
>  	 */
>  	bool multishot = kasan_save_enable_multi_shot();
>  
> -- 
> 2.29.2.729.g45daf8777d-goog
> 

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