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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 DFBA4C433B4 for ; Sat, 15 May 2021 00:27:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7EE26145B for ; Sat, 15 May 2021 00:27:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234522AbhEOA2l (ORCPT ); Fri, 14 May 2021 20:28:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:43912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230022AbhEOA2k (ORCPT ); Fri, 14 May 2021 20:28:40 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2E13261176; Sat, 15 May 2021 00:27:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1621038448; bh=bSGxouT3kOSPsbFK7LM4HYQDu0TSOgVamWpI66joQqU=; h=Date:From:To:Subject:In-Reply-To:From; b=MVhk/ftv2XEmif8cs8Sat4o7zjUpCR2ILVcYrfeKc9E5br/mhkRUUZpXBxMu5D4zU BveyxaXhEoGZNwcoX5/IZiSgReUdTw3vMeCoDT6yNvG4pRnf+mUZidT/kGqJwZ3z2+ xeMR1v+hQqRTj40aFyi8qRLjZrXsDKFkgz1x++qg= Date: Fri, 14 May 2021 17:27:27 -0700 From: Andrew Morton To: akpm@linux-foundation.org, andreyknvl@gmail.com, eugenis@google.com, georgepope@android.com, glider@google.com, lenaptr@google.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, pcc@google.com, stable@vger.kernel.org, torvalds@linux-foundation.org Subject: [patch 09/13] kasan: fix unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled Message-ID: <20210515002727.2LmnD7uG3%akpm@linux-foundation.org> In-Reply-To: <20210514172634.9018621171d5334ceee97e95@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Peter Collingbourne Subject: kasan: fix unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled These tests deliberately access these arrays out of bounds, which will cause the dynamic local bounds checks inserted by CONFIG_UBSAN_LOCAL_BOUNDS to fail and panic the kernel. To avoid this problem, access the arrays via volatile pointers, which will prevent the compiler from being able to determine the array bounds. These accesses use volatile pointers to char (char *volatile) rather than the more conventional pointers to volatile char (volatile char *) because we want to prevent the compiler from making inferences about the pointer itself (i.e. its array bounds), not the data that it refers to. Link: https://lkml.kernel.org/r/20210507025915.1464056-1-pcc@google.com Link: https://linux-review.googlesource.com/id/I90b1713fbfa1bf68ff895aef099ea77b98a7c3b9 Signed-off-by: Peter Collingbourne Tested-by: Alexander Potapenko Reviewed-by: Andrey Konovalov Cc: Peter Collingbourne Cc: George Popescu Cc: Elena Petrova Cc: Evgenii Stepanov Cc: Signed-off-by: Andrew Morton --- lib/test_kasan.c | 29 +++++++++++++++++++++++------ 1 file changed, 23 insertions(+), 6 deletions(-) --- a/lib/test_kasan.c~kasan-fix-unit-tests-with-config_ubsan_local_bounds-enabled +++ a/lib/test_kasan.c @@ -654,8 +654,20 @@ static char global_array[10]; static void kasan_global_oob(struct kunit *test) { - volatile int i = 3; - char *p = &global_array[ARRAY_SIZE(global_array) + i]; + /* + * Deliberate out-of-bounds access. To prevent CONFIG_UBSAN_LOCAL_BOUNDS + * from failing here and panicing the kernel, access the array via a + * volatile pointer, which will prevent the compiler from being able to + * determine the array bounds. + * + * This access uses a volatile pointer to char (char *volatile) rather + * than the more conventional pointer to volatile char (volatile char *) + * because we want to prevent the compiler from making inferences about + * the pointer itself (i.e. its array bounds), not the data that it + * refers to. + */ + char *volatile array = global_array; + char *p = &array[ARRAY_SIZE(global_array) + 3]; /* Only generic mode instruments globals. */ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC); @@ -703,8 +715,9 @@ static void ksize_uaf(struct kunit *test static void kasan_stack_oob(struct kunit *test) { char stack_array[10]; - volatile int i = OOB_TAG_OFF; - char *p = &stack_array[ARRAY_SIZE(stack_array) + i]; + /* See comment in kasan_global_oob. */ + char *volatile array = stack_array; + char *p = &array[ARRAY_SIZE(stack_array) + OOB_TAG_OFF]; KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_STACK); @@ -715,7 +728,9 @@ static void kasan_alloca_oob_left(struct { volatile int i = 10; char alloca_array[i]; - char *p = alloca_array - 1; + /* See comment in kasan_global_oob. */ + char *volatile array = alloca_array; + char *p = array - 1; /* Only generic mode instruments dynamic allocas. */ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC); @@ -728,7 +743,9 @@ static void kasan_alloca_oob_right(struc { volatile int i = 10; char alloca_array[i]; - char *p = alloca_array + i; + /* See comment in kasan_global_oob. */ + char *volatile array = alloca_array; + char *p = array + i; /* Only generic mode instruments dynamic allocas. */ KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC); _