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Date:   Fri, 13 Jan 2023 16:57:59 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        David Gow <davidgow@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        linux-hardening@vger.kernel.org, Vlastimil Babka <vbabka@suse.cz>,
        Daniel Latypov <dlatypov@google.com>,
        Josh Poimboeuf <jpoimboe@kernel.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Miguel Ojeda <ojeda@kernel.org>,
        Isabella Basso <isabbasso@riseup.net>,
        Dan Williams <dan.j.williams@intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kunit: memcpy: Split slow memcpy tests into
 MEMCPY_SLOW_KUNIT_TEST
Message-ID: <202301131657.8E076628@keescook>
References: <20230114005408.never.756-kees@kernel.org>
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gah. this is actually v2. :(

On Fri, Jan 13, 2023 at 04:54:12PM -0800, Kees Cook wrote:
> Since the long memcpy tests may stall a system for tens of seconds
> in virtualized architecture environments, split those tests off under
> CONFIG_MEMCPY_SLOW_KUNIT_TEST so they can be separately disabled.
> 
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Link: https://lore.kernel.org/lkml/20221226195206.GA2626419@roeck-us.net
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-and-tested-by: Guenter Roeck <linux@roeck-us.net>
> Reviewed-by: David Gow <davidgow@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v2: fix tristate to bool
> v1: https://lore.kernel.org/lkml/20230107040203.never.112-kees@kernel.org
> ---
>  lib/Kconfig.debug  |  9 +++++++++
>  lib/memcpy_kunit.c | 15 ++++++++++++---
>  2 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index c2c78d0e761c..f90637171453 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2621,6 +2621,15 @@ config MEMCPY_KUNIT_TEST
>  
>  	  If unsure, say N.
>  
> +config MEMCPY_SLOW_KUNIT_TEST
> +	bool "Include exhaustive memcpy tests" if !KUNIT_ALL_TESTS
> +	depends on MEMCPY_KUNIT_TEST
> +	default KUNIT_ALL_TESTS
> +	help
> +	  Some memcpy tests are quite exhaustive in checking for overlaps
> +	  and bit ranges. These can be very slow, so they are split out
> +	  as a separate config.
> +
>  config IS_SIGNED_TYPE_KUNIT_TEST
>  	tristate "Test is_signed_type() macro" if !KUNIT_ALL_TESTS
>  	depends on KUNIT
> diff --git a/lib/memcpy_kunit.c b/lib/memcpy_kunit.c
> index 89128551448d..5a545e1b5dbb 100644
> --- a/lib/memcpy_kunit.c
> +++ b/lib/memcpy_kunit.c
> @@ -307,8 +307,12 @@ static void set_random_nonzero(struct kunit *test, u8 *byte)
>  	}
>  }
>  
> -static void init_large(struct kunit *test)
> +static int init_large(struct kunit *test)
>  {
> +	if (!IS_ENABLED(CONFIG_MEMCPY_SLOW_KUNIT_TEST)) {
> +		kunit_skip(test, "Slow test skipped. Enable with CONFIG_MEMCPY_SLOW_KUNIT_TEST=y");
> +		return -EBUSY;
> +	}
>  
>  	/* Get many bit patterns. */
>  	get_random_bytes(large_src, ARRAY_SIZE(large_src));
> @@ -319,6 +323,8 @@ static void init_large(struct kunit *test)
>  
>  	/* Explicitly zero the entire destination. */
>  	memset(large_dst, 0, ARRAY_SIZE(large_dst));
> +
> +	return 0;
>  }
>  
>  /*
> @@ -327,7 +333,9 @@ static void init_large(struct kunit *test)
>   */
>  static void copy_large_test(struct kunit *test, bool use_memmove)
>  {
> -	init_large(test);
> +
> +	if (init_large(test))
> +		return;
>  
>  	/* Copy a growing number of non-overlapping bytes ... */
>  	for (int bytes = 1; bytes <= ARRAY_SIZE(large_src); bytes++) {
> @@ -472,7 +480,8 @@ static void memmove_overlap_test(struct kunit *test)
>  	static const int bytes_start = 1;
>  	static const int bytes_end = ARRAY_SIZE(large_src) + 1;
>  
> -	init_large(test);
> +	if (init_large(test))
> +		return;
>  
>  	/* Copy a growing number of overlapping bytes ... */
>  	for (int bytes = bytes_start; bytes < bytes_end;
> -- 
> 2.34.1
> 

-- 
Kees Cook