From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C4B7C433DF for ; Wed, 3 Jun 2020 22:56:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id F191320659 for ; Wed, 3 Jun 2020 22:56:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="mAh8GtBS" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F191320659 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 9C4FC280009; Wed, 3 Jun 2020 18:56:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 94F58280003; Wed, 3 Jun 2020 18:56:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8171B280009; Wed, 3 Jun 2020 18:56:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0037.hostedemail.com [216.40.44.37]) by kanga.kvack.org (Postfix) with ESMTP id 63C1C280003 for ; Wed, 3 Jun 2020 18:56:46 -0400 (EDT) Received: from smtpin25.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 34456181AEF09 for ; Wed, 3 Jun 2020 22:56:46 +0000 (UTC) X-FDA: 76889412012.25.drum25_d14b2dc0024 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin25.hostedemail.com (Postfix) with ESMTP id 0EEAC1804E3A0 for ; Wed, 3 Jun 2020 22:56:46 +0000 (UTC) X-HE-Tag: drum25_d14b2dc0024 X-Filterd-Recvd-Size: 7231 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Wed, 3 Jun 2020 22:56:45 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1200620734; Wed, 3 Jun 2020 22:56:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591225004; bh=P4xu64ApR2ejvlybB8SI55WM30pJfGDBSDtHHZf/4gw=; h=Date:From:To:Subject:In-Reply-To:From; b=mAh8GtBSEquFgdiVIUNBmRczM954Sr/vABIUHyc58p39UxqPgfV7/wKW2vCg52fW2 a++ONrS9n8pfizTZp0qc57kUrIImywl8IHzDrLS9558+2DIah33ZJvYH3XQ595UHKv abT9q6k39Bu2UoEmrQACMlpaVa1xDy1O26dBwxhM= Date: Wed, 03 Jun 2020 15:56:43 -0700 From: Andrew Morton To: akpm@linux-foundation.org, aryabinin@virtuozzo.com, danielmicay@gmail.com, davidgow@google.com, dja@axtens.net, dvyukov@google.com, glider@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 008/131] kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE Message-ID: <20200603225643.BSVxCW3H1%akpm@linux-foundation.org> In-Reply-To: <20200603155549.e041363450869eaae4c7f05b@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Queue-Id: 0EEAC1804E3A0 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Daniel Axtens Subject: kasan: stop tests being eliminated as dead code with FORTIFY_SOURCE Patch series "Fix some incompatibilites between KASAN and FORTIFY_SOURCE", v4. 3 KASAN self-tests fail on a kernel with both KASAN and FORTIFY_SOURCE: memchr, memcmp and strlen. When FORTIFY_SOURCE is on, a number of functions are replaced with fortified versions, which attempt to check the sizes of the operands. However, these functions often directly invoke __builtin_foo() once they have performed the fortify check. The compiler can detect that the results of these functions are not used, and knows that they have no other side effects, and so can eliminate them as dead code. Why are only memchr, memcmp and strlen affected? ================================================ Of string and string-like functions, kasan_test tests: * strchr -> not affected, no fortified version * strrchr -> likewise * strcmp -> likewise * strncmp -> likewise * strnlen -> not affected, the fortify source implementation calls the underlying strnlen implementation which is instrumented, not a builtin * strlen -> affected, the fortify souce implementation calls a __builtin version which the compiler can determine is dead. * memchr -> likewise * memcmp -> likewise * memset -> not affected, the compiler knows that memset writes to its first argument and therefore is not dead. Why does this not affect the functions normally? ================================================ In string.h, these functions are not marked as __pure, so the compiler cannot know that they do not have side effects. If relevant functions are marked as __pure in string.h, we see the following warnings and the functions are elided: lib/test_kasan.c: In function `kasan_memchr': lib/test_kasan.c:606:2: warning: statement with no effect [-Wunused-value] memchr(ptr, '1', size + 1); ^~~~~~~~~~~~~~~~~~~~~~~~~~ lib/test_kasan.c: In function `kasan_memcmp': lib/test_kasan.c:622:2: warning: statement with no effect [-Wunused-value] memcmp(ptr, arr, size+1); ^~~~~~~~~~~~~~~~~~~~~~~~ lib/test_kasan.c: In function `kasan_strings': lib/test_kasan.c:645:2: warning: statement with no effect [-Wunused-value] strchr(ptr, '1'); ^~~~~~~~~~~~~~~~ ... This annotation would make sense to add and could be added at any point, so the behaviour of test_kasan.c should change. The fix ======= Make all the functions that are pure write their results to a global, which makes them live. The strlen and memchr tests now pass. The memcmp test still fails to trigger, which is addressed in the next patch. [dja@axtens.net: drop patch 3] Link: http://lkml.kernel.org/r/20200424145521.8203-2-dja@axtens.net Link: http://lkml.kernel.org/r/20200423154503.5103-1-dja@axtens.net Link: http://lkml.kernel.org/r/20200423154503.5103-2-dja@axtens.net Fixes: 0c96350a2d2f ("lib/test_kasan.c: add tests for several string/memory API functions") Signed-off-by: Daniel Axtens Reviewed-by: Dmitry Vyukov Tested-by: David Gow Cc: Daniel Micay Cc: Andrey Ryabinin Cc: Alexander Potapenko Signed-off-by: Andrew Morton --- lib/test_kasan.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) --- a/lib/test_kasan.c~kasan-stop-tests-being-eliminated-as-dead-code-with-fortify_source +++ a/lib/test_kasan.c @@ -24,6 +24,14 @@ #include /* + * We assign some test results to these globals to make sure the tests + * are not eliminated as dead code. + */ + +int kasan_int_result; +void *kasan_ptr_result; + +/* * Note: test functions are marked noinline so that their names appear in * reports. */ @@ -622,7 +630,7 @@ static noinline void __init kasan_memchr if (!ptr) return; - memchr(ptr, '1', size + 1); + kasan_ptr_result = memchr(ptr, '1', size + 1); kfree(ptr); } @@ -638,7 +646,7 @@ static noinline void __init kasan_memcmp return; memset(arr, 0, sizeof(arr)); - memcmp(ptr, arr, size+1); + kasan_int_result = memcmp(ptr, arr, size + 1); kfree(ptr); } @@ -661,22 +669,22 @@ static noinline void __init kasan_string * will likely point to zeroed byte. */ ptr += 16; - strchr(ptr, '1'); + kasan_ptr_result = strchr(ptr, '1'); pr_info("use-after-free in strrchr\n"); - strrchr(ptr, '1'); + kasan_ptr_result = strrchr(ptr, '1'); pr_info("use-after-free in strcmp\n"); - strcmp(ptr, "2"); + kasan_int_result = strcmp(ptr, "2"); pr_info("use-after-free in strncmp\n"); - strncmp(ptr, "2", 1); + kasan_int_result = strncmp(ptr, "2", 1); pr_info("use-after-free in strlen\n"); - strlen(ptr); + kasan_int_result = strlen(ptr); pr_info("use-after-free in strnlen\n"); - strnlen(ptr, 1); + kasan_int_result = strnlen(ptr, 1); } static noinline void __init kasan_bitops(void) @@ -743,11 +751,12 @@ static noinline void __init kasan_bitops __test_and_change_bit(BITS_PER_LONG + BITS_PER_BYTE, bits); pr_info("out-of-bounds in test_bit\n"); - (void)test_bit(BITS_PER_LONG + BITS_PER_BYTE, bits); + kasan_int_result = test_bit(BITS_PER_LONG + BITS_PER_BYTE, bits); #if defined(clear_bit_unlock_is_negative_byte) pr_info("out-of-bounds in clear_bit_unlock_is_negative_byte\n"); - clear_bit_unlock_is_negative_byte(BITS_PER_LONG + BITS_PER_BYTE, bits); + kasan_int_result = clear_bit_unlock_is_negative_byte(BITS_PER_LONG + + BITS_PER_BYTE, bits); #endif kfree(bits); } _