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=-9.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 4C862C33CB1 for ; Thu, 16 Jan 2020 06:26:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 09D752075B for ; Thu, 16 Jan 2020 06:26:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=axtens.net header.i=@axtens.net header.b="Uhihq+6r" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730710AbgAPG0l (ORCPT ); Thu, 16 Jan 2020 01:26:41 -0500 Received: from mail-pl1-f196.google.com ([209.85.214.196]:46319 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730684AbgAPG0k (ORCPT ); Thu, 16 Jan 2020 01:26:40 -0500 Received: by mail-pl1-f196.google.com with SMTP id y8so7884575pll.13 for ; Wed, 15 Jan 2020 22:26:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=axtens.net; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=ecViW2B6K6MgjtfxW3TT7mCoLEuRKAGSK4ebp685lGI=; b=Uhihq+6rfB5UyQl+9UDv+i3ThvZFs5H/8nw3PJ9UAbz3R2r3AMJzgomMFAzOXhQixb 9c4b8qrhyrPfdzEOkv05oUMvhz2JnmwO7kdW6N8LsZbFuuF4bvwkNyNZ4AOA+k+w3p4A vn7BPofvQmrLxHWpcX8lHyw7JZ1dUbkAXFCGQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=ecViW2B6K6MgjtfxW3TT7mCoLEuRKAGSK4ebp685lGI=; b=H0rVHJywUklkahjnWtJxdnBhvZtBJ6NsOOARsw5hUc0ZCMZ0z40yTm9e3X6nXMPbtu 2N6pnAeoqR85k6EbnA72pFPyQJVdhjP5zZWUYacuE4YthnXS+Cy48CA4DPK1TCm99Zgk ZbLF6h5X1vmdxTKk/yS8Gy4F9kmXXzSAKth9I2N/KpjMXZU84MJXg0ZxHJVzD4XaNijG 4hIRL5hJKRgBBNRO44Yi6Te8Pu3lDvqeWoY8MW/DfCDzWEUhplK9VDj0hOSGWg7+x9qQ l5n3e6/0mUFRwym6AyV7g027WDwbIT2cfI3pIaHN+z3n6NsJ/Ifmed+kr0VjEKVxeSTx k2Pg== X-Gm-Message-State: APjAAAWv+VFiG0h9LcMG+azCAmuETdbIKFV7ZkHyhRBI3khuhymcA//R qg3Z+5PMTUEcphiUdAHqPPnMEABT0co= X-Google-Smtp-Source: APXvYqw19UTxY8Hi9APh86aEtqUHLB8ch68t3FABEMRmpJHJbbxu4RZM4Mz69GnkzexI90XRmebJvQ== X-Received: by 2002:a17:90a:a608:: with SMTP id c8mr4785355pjq.36.1579155999384; Wed, 15 Jan 2020 22:26:39 -0800 (PST) Received: from localhost (2001-44b8-1113-6700-097c-7eed-afd4-cd15.static.ipv6.internode.on.net. [2001:44b8:1113:6700:97c:7eed:afd4:cd15]) by smtp.gmail.com with ESMTPSA id o16sm22735174pgl.58.2020.01.15.22.26.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2020 22:26:38 -0800 (PST) From: Daniel Axtens To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com Cc: linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-s390@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, dvyukov@google.com, christophe.leroy@c-s.fr, Daniel Axtens , Daniel Micay , Andrey Ryabinin , Alexander Potapenko Subject: [PATCH v2 2/3] string.h: fix incompatibility between FORTIFY_SOURCE and KASAN Date: Thu, 16 Jan 2020 17:26:24 +1100 Message-Id: <20200116062625.32692-3-dja@axtens.net> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200116062625.32692-1-dja@axtens.net> References: <20200116062625.32692-1-dja@axtens.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The memcmp KASAN self-test fails on a kernel with both KASAN and FORTIFY_SOURCE. 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. Using __builtins may bypass KASAN checks if the compiler decides to inline it's own implementation as sequence of instructions, rather than emit a function call that goes out to a KASAN-instrumented implementation. Why is only memcmp affected? ============================ Of the string and string-like functions that kasan_test tests, only memcmp is replaced by an inline sequence of instructions in my testing on x86 with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2). I believe this is due to compiler heuristics. For example, if I annotate kmalloc calls with the alloc_size annotation (and disable some fortify compile-time checking!), the compiler will replace every memset except the one in kmalloc_uaf_memset with inline instructions. (I have some WIP patches to add this annotation.) Does this affect other functions in string.h? ============================================= Yes. Anything that uses __builtin_* rather than __real_* could be affected. This looks like: - strncpy - strcat - strlen - strlcpy maybe, under some circumstances? - strncat under some circumstances - memset - memcpy - memmove - memcmp (as noted) - memchr - strcpy Whether a function call is emitted always depends on the compiler. Most bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows that this is not always the case. Isn't FORTIFY_SOURCE disabled with KASAN? ========================================- The string headers on all arches supporting KASAN disable fortify with kasan, but only when address sanitisation is _also_ disabled. For example from x86: #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__) /* * For files that are not instrumented (e.g. mm/slub.c) we * should use not instrumented version of mem* functions. */ #define memcpy(dst, src, len) __memcpy(dst, src, len) #define memmove(dst, src, len) __memmove(dst, src, len) #define memset(s, c, n) __memset(s, c, n) #ifndef __NO_FORTIFY #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */ #endif #endif This comes from commit 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions"), and doesn't work when KASAN is enabled and the file is supposed to be sanitised - as with test_kasan.c I'm pretty sure this is not wrong, but not as expansive it should be: * we shouldn't use __builtin_memcpy etc in files where we don't have instrumentation - it could devolve into a function call to memcpy, which will be instrumented. Rather, we should use __memcpy which by convention is not instrumented. * we also shouldn't be using __builtin_memcpy when we have a KASAN instrumented file, because it could be replaced with inline asm that will not be instrumented. What is correct behaviour? ========================== Firstly, there is some overlap between fortification and KASAN: both provide some level of _runtime_ checking. Only fortify provides compile-time checking. KASAN and fortify can pick up different things at runtime: - Some fortify functions, notably the string functions, could easily be modified to consider sub-object sizes (e.g. members within a struct), and I have some WIP patches to do this. KASAN cannot detect these because it cannot insert poision between members of a struct. - KASAN can detect many over-reads/over-writes when the sizes of both operands are unknown, which fortify cannot. So there are a couple of options: 1) Flip the test: disable fortify in santised files and enable it in unsanitised files. This at least stops us missing KASAN checking, but we lose the fortify checking. 2) Make the fortify code always call out to real versions. Do this only for KASAN, for fear of losing the inlining opportunities we get from __builtin_*. (We can't use kasan_check_{read,write}: because the fortify functions are _extern inline_, you can't include _static_ inline functions without a compiler warning. kasan_check_{read,write} are static inline so we can't use them even when they would otherwise be suitable.) Take approach 2 and call out to real versions when KASAN is enabled. Use __underlying_foo to distinguish from __real_foo: __real_foo always refers to the kernel's implementation of foo, __underlying_foo could be either the kernel implementation or the __builtin_foo implementation. This is sometimes enough to make the memcmp test succeed with FORTIFY_SOURCE enabled. It is at least enough to get the function call into the module. One more fix is needed to make it reliable: see the next patch. Cc: Daniel Micay Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Dmitry Vyukov Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions") Signed-off-by: Daniel Axtens --- v2: add #undefs, do not drop arch code: Dmitry pointed out that we _do_ want to disable fortify in non-sanitised files because of how __builtin_memcpy might end up as a call to regular memcpy rather than __memcpy. Dmitry, this might cause a few new syzkaller splats - I first picked it up building from a syskaller config. Or it might not, it just depends what gets replaced with an inline sequence of instructions. checkpatch complains about some over-long lines, happy to change the format if anyone has better ideas for how to lay it out. --- include/linux/string.h | 60 +++++++++++++++++++++++++++++++++--------- 1 file changed, 48 insertions(+), 12 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index 3b8e8b12dd37..18d3f7a4b2b9 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -317,6 +317,31 @@ void __read_overflow3(void) __compiletime_error("detected read beyond size of ob void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter"); #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE) + +#ifdef CONFIG_KASAN +extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr); +extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp); +extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy); +extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove); +extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset); +extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat); +extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy); +extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen); +extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat); +extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy); +#else +#define __underlying_memchr __builtin_memchr +#define __underlying_memcmp __builtin_memcmp +#define __underlying_memcpy __builtin_memcpy +#define __underlying_memmove __builtin_memmove +#define __underlying_memset __builtin_memset +#define __underlying_strcat __builtin_strcat +#define __underlying_strcpy __builtin_strcpy +#define __underlying_strlen __builtin_strlen +#define __underlying_strncat __builtin_strncat +#define __underlying_strncpy __builtin_strncpy +#endif + __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 0); @@ -324,14 +349,14 @@ __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) __write_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_strncpy(p, q, size); + return __underlying_strncpy(p, q, size); } __FORTIFY_INLINE char *strcat(char *p, const char *q) { size_t p_size = __builtin_object_size(p, 0); if (p_size == (size_t)-1) - return __builtin_strcat(p, q); + return __underlying_strcat(p, q); if (strlcat(p, q, p_size) >= p_size) fortify_panic(__func__); return p; @@ -345,7 +370,7 @@ __FORTIFY_INLINE __kernel_size_t strlen(const char *p) /* Work around gcc excess stack consumption issue */ if (p_size == (size_t)-1 || (__builtin_constant_p(p[p_size - 1]) && p[p_size - 1] == '\0')) - return __builtin_strlen(p); + return __underlying_strlen(p); ret = strnlen(p, p_size); if (p_size <= ret) fortify_panic(__func__); @@ -378,7 +403,7 @@ __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size) __write_overflow(); if (len >= p_size) fortify_panic(__func__); - __builtin_memcpy(p, q, len); + __underlying_memcpy(p, q, len); p[len] = '\0'; } return ret; @@ -391,12 +416,12 @@ __FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); if (p_size == (size_t)-1 && q_size == (size_t)-1) - return __builtin_strncat(p, q, count); + return __underlying_strncat(p, q, count); p_len = strlen(p); copy_len = strnlen(q, count); if (p_size < p_len + copy_len + 1) fortify_panic(__func__); - __builtin_memcpy(p + p_len, q, copy_len); + __underlying_memcpy(p + p_len, q, copy_len); p[p_len + copy_len] = '\0'; return p; } @@ -408,7 +433,7 @@ __FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size) __write_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_memset(p, c, size); + return __underlying_memset(p, c, size); } __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) @@ -423,7 +448,7 @@ __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memcpy(p, q, size); + return __underlying_memcpy(p, q, size); } __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) @@ -438,7 +463,7 @@ __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memmove(p, q, size); + return __underlying_memmove(p, q, size); } extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); @@ -464,7 +489,7 @@ __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memcmp(p, q, size); + return __underlying_memcmp(p, q, size); } __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) @@ -474,7 +499,7 @@ __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) __read_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_memchr(p, c, size); + return __underlying_memchr(p, c, size); } void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); @@ -505,11 +530,22 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q) size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); if (p_size == (size_t)-1 && q_size == (size_t)-1) - return __builtin_strcpy(p, q); + return __underlying_strcpy(p, q); memcpy(p, q, strlen(q) + 1); return p; } +/* Don't use these outside the FORITFY_SOURCE implementation */ +#undef __underlying_memchr +#undef __underlying_memcmp +#undef __underlying_memcpy +#undef __underlying_memmove +#undef __underlying_memset +#undef __underlying_strcat +#undef __underlying_strcpy +#undef __underlying_strlen +#undef __underlying_strncat +#undef __underlying_strncpy #endif /** -- 2.20.1 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=-9.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 BC3F9C33CB1 for ; Thu, 16 Jan 2020 06:33:00 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 42F262077B for ; Thu, 16 Jan 2020 06:33:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=axtens.net header.i=@axtens.net header.b="Uhihq+6r" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 42F262077B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=axtens.net Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 47yvWt3VVGzDqXS for ; Thu, 16 Jan 2020 17:32:58 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=axtens.net (client-ip=2607:f8b0:4864:20::1041; helo=mail-pj1-x1041.google.com; envelope-from=dja@axtens.net; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=axtens.net Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=axtens.net header.i=@axtens.net header.a=rsa-sha256 header.s=google header.b=Uhihq+6r; dkim-atps=neutral Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 47yvNf4100zDqW2 for ; Thu, 16 Jan 2020 17:26:42 +1100 (AEDT) Received: by mail-pj1-x1041.google.com with SMTP id n59so1086969pjb.1 for ; Wed, 15 Jan 2020 22:26:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=axtens.net; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=ecViW2B6K6MgjtfxW3TT7mCoLEuRKAGSK4ebp685lGI=; b=Uhihq+6rfB5UyQl+9UDv+i3ThvZFs5H/8nw3PJ9UAbz3R2r3AMJzgomMFAzOXhQixb 9c4b8qrhyrPfdzEOkv05oUMvhz2JnmwO7kdW6N8LsZbFuuF4bvwkNyNZ4AOA+k+w3p4A vn7BPofvQmrLxHWpcX8lHyw7JZ1dUbkAXFCGQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=ecViW2B6K6MgjtfxW3TT7mCoLEuRKAGSK4ebp685lGI=; b=jCc+EI3fZ1hi2t2/TRxbMauOZw68CWlgdsgvGbv0wdeSUosMfkyQeoFzV8j09ruplS TJXS79FJhpRA+HZeTDmAGEBG7b1AdR/ib/6qQTbaQydjivpWv4PR+ywaRA2E6es//TH8 1AzXPz2gcSk7xIvI8oIf+kpSFfIIOdUmusUCydaSmbVFRMRN0NLfStUV/fsYOgC22KO8 OM0PdEihKy/wy+SWWW8Pabxs612gJx07dC0d6e0w3XVBULHT8+DFVrtswTmcKe8Kc3/g sSHGBpiN2lD8hr41RDuYmCKtj/Tlg6ecqpALPcblmtmLKzfjrFsRD263qwKrDcP+XXnT xYwA== X-Gm-Message-State: APjAAAXgmJRqSGKh4GdQIrlFGEPRpf33uyW/kTBqiyeBA89/3wa5usAa Qt1iInzc5gc5DIO5zMg16JIF5w== X-Google-Smtp-Source: APXvYqw19UTxY8Hi9APh86aEtqUHLB8ch68t3FABEMRmpJHJbbxu4RZM4Mz69GnkzexI90XRmebJvQ== X-Received: by 2002:a17:90a:a608:: with SMTP id c8mr4785355pjq.36.1579155999384; Wed, 15 Jan 2020 22:26:39 -0800 (PST) Received: from localhost (2001-44b8-1113-6700-097c-7eed-afd4-cd15.static.ipv6.internode.on.net. [2001:44b8:1113:6700:97c:7eed:afd4:cd15]) by smtp.gmail.com with ESMTPSA id o16sm22735174pgl.58.2020.01.15.22.26.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2020 22:26:38 -0800 (PST) From: Daniel Axtens To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com Subject: [PATCH v2 2/3] string.h: fix incompatibility between FORTIFY_SOURCE and KASAN Date: Thu, 16 Jan 2020 17:26:24 +1100 Message-Id: <20200116062625.32692-3-dja@axtens.net> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200116062625.32692-1-dja@axtens.net> References: <20200116062625.32692-1-dja@axtens.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-s390@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, Daniel Micay , Alexander Potapenko , linux-arm-kernel@lists.infradead.org, Andrey Ryabinin , linuxppc-dev@lists.ozlabs.org, dvyukov@google.com, Daniel Axtens Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" The memcmp KASAN self-test fails on a kernel with both KASAN and FORTIFY_SOURCE. 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. Using __builtins may bypass KASAN checks if the compiler decides to inline it's own implementation as sequence of instructions, rather than emit a function call that goes out to a KASAN-instrumented implementation. Why is only memcmp affected? ============================ Of the string and string-like functions that kasan_test tests, only memcmp is replaced by an inline sequence of instructions in my testing on x86 with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2). I believe this is due to compiler heuristics. For example, if I annotate kmalloc calls with the alloc_size annotation (and disable some fortify compile-time checking!), the compiler will replace every memset except the one in kmalloc_uaf_memset with inline instructions. (I have some WIP patches to add this annotation.) Does this affect other functions in string.h? ============================================= Yes. Anything that uses __builtin_* rather than __real_* could be affected. This looks like: - strncpy - strcat - strlen - strlcpy maybe, under some circumstances? - strncat under some circumstances - memset - memcpy - memmove - memcmp (as noted) - memchr - strcpy Whether a function call is emitted always depends on the compiler. Most bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows that this is not always the case. Isn't FORTIFY_SOURCE disabled with KASAN? ========================================- The string headers on all arches supporting KASAN disable fortify with kasan, but only when address sanitisation is _also_ disabled. For example from x86: #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__) /* * For files that are not instrumented (e.g. mm/slub.c) we * should use not instrumented version of mem* functions. */ #define memcpy(dst, src, len) __memcpy(dst, src, len) #define memmove(dst, src, len) __memmove(dst, src, len) #define memset(s, c, n) __memset(s, c, n) #ifndef __NO_FORTIFY #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */ #endif #endif This comes from commit 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions"), and doesn't work when KASAN is enabled and the file is supposed to be sanitised - as with test_kasan.c I'm pretty sure this is not wrong, but not as expansive it should be: * we shouldn't use __builtin_memcpy etc in files where we don't have instrumentation - it could devolve into a function call to memcpy, which will be instrumented. Rather, we should use __memcpy which by convention is not instrumented. * we also shouldn't be using __builtin_memcpy when we have a KASAN instrumented file, because it could be replaced with inline asm that will not be instrumented. What is correct behaviour? ========================== Firstly, there is some overlap between fortification and KASAN: both provide some level of _runtime_ checking. Only fortify provides compile-time checking. KASAN and fortify can pick up different things at runtime: - Some fortify functions, notably the string functions, could easily be modified to consider sub-object sizes (e.g. members within a struct), and I have some WIP patches to do this. KASAN cannot detect these because it cannot insert poision between members of a struct. - KASAN can detect many over-reads/over-writes when the sizes of both operands are unknown, which fortify cannot. So there are a couple of options: 1) Flip the test: disable fortify in santised files and enable it in unsanitised files. This at least stops us missing KASAN checking, but we lose the fortify checking. 2) Make the fortify code always call out to real versions. Do this only for KASAN, for fear of losing the inlining opportunities we get from __builtin_*. (We can't use kasan_check_{read,write}: because the fortify functions are _extern inline_, you can't include _static_ inline functions without a compiler warning. kasan_check_{read,write} are static inline so we can't use them even when they would otherwise be suitable.) Take approach 2 and call out to real versions when KASAN is enabled. Use __underlying_foo to distinguish from __real_foo: __real_foo always refers to the kernel's implementation of foo, __underlying_foo could be either the kernel implementation or the __builtin_foo implementation. This is sometimes enough to make the memcmp test succeed with FORTIFY_SOURCE enabled. It is at least enough to get the function call into the module. One more fix is needed to make it reliable: see the next patch. Cc: Daniel Micay Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Dmitry Vyukov Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions") Signed-off-by: Daniel Axtens --- v2: add #undefs, do not drop arch code: Dmitry pointed out that we _do_ want to disable fortify in non-sanitised files because of how __builtin_memcpy might end up as a call to regular memcpy rather than __memcpy. Dmitry, this might cause a few new syzkaller splats - I first picked it up building from a syskaller config. Or it might not, it just depends what gets replaced with an inline sequence of instructions. checkpatch complains about some over-long lines, happy to change the format if anyone has better ideas for how to lay it out. --- include/linux/string.h | 60 +++++++++++++++++++++++++++++++++--------- 1 file changed, 48 insertions(+), 12 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index 3b8e8b12dd37..18d3f7a4b2b9 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -317,6 +317,31 @@ void __read_overflow3(void) __compiletime_error("detected read beyond size of ob void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter"); #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE) + +#ifdef CONFIG_KASAN +extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr); +extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp); +extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy); +extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove); +extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset); +extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat); +extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy); +extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen); +extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat); +extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy); +#else +#define __underlying_memchr __builtin_memchr +#define __underlying_memcmp __builtin_memcmp +#define __underlying_memcpy __builtin_memcpy +#define __underlying_memmove __builtin_memmove +#define __underlying_memset __builtin_memset +#define __underlying_strcat __builtin_strcat +#define __underlying_strcpy __builtin_strcpy +#define __underlying_strlen __builtin_strlen +#define __underlying_strncat __builtin_strncat +#define __underlying_strncpy __builtin_strncpy +#endif + __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 0); @@ -324,14 +349,14 @@ __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) __write_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_strncpy(p, q, size); + return __underlying_strncpy(p, q, size); } __FORTIFY_INLINE char *strcat(char *p, const char *q) { size_t p_size = __builtin_object_size(p, 0); if (p_size == (size_t)-1) - return __builtin_strcat(p, q); + return __underlying_strcat(p, q); if (strlcat(p, q, p_size) >= p_size) fortify_panic(__func__); return p; @@ -345,7 +370,7 @@ __FORTIFY_INLINE __kernel_size_t strlen(const char *p) /* Work around gcc excess stack consumption issue */ if (p_size == (size_t)-1 || (__builtin_constant_p(p[p_size - 1]) && p[p_size - 1] == '\0')) - return __builtin_strlen(p); + return __underlying_strlen(p); ret = strnlen(p, p_size); if (p_size <= ret) fortify_panic(__func__); @@ -378,7 +403,7 @@ __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size) __write_overflow(); if (len >= p_size) fortify_panic(__func__); - __builtin_memcpy(p, q, len); + __underlying_memcpy(p, q, len); p[len] = '\0'; } return ret; @@ -391,12 +416,12 @@ __FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); if (p_size == (size_t)-1 && q_size == (size_t)-1) - return __builtin_strncat(p, q, count); + return __underlying_strncat(p, q, count); p_len = strlen(p); copy_len = strnlen(q, count); if (p_size < p_len + copy_len + 1) fortify_panic(__func__); - __builtin_memcpy(p + p_len, q, copy_len); + __underlying_memcpy(p + p_len, q, copy_len); p[p_len + copy_len] = '\0'; return p; } @@ -408,7 +433,7 @@ __FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size) __write_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_memset(p, c, size); + return __underlying_memset(p, c, size); } __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) @@ -423,7 +448,7 @@ __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memcpy(p, q, size); + return __underlying_memcpy(p, q, size); } __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) @@ -438,7 +463,7 @@ __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memmove(p, q, size); + return __underlying_memmove(p, q, size); } extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); @@ -464,7 +489,7 @@ __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memcmp(p, q, size); + return __underlying_memcmp(p, q, size); } __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) @@ -474,7 +499,7 @@ __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) __read_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_memchr(p, c, size); + return __underlying_memchr(p, c, size); } void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); @@ -505,11 +530,22 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q) size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); if (p_size == (size_t)-1 && q_size == (size_t)-1) - return __builtin_strcpy(p, q); + return __underlying_strcpy(p, q); memcpy(p, q, strlen(q) + 1); return p; } +/* Don't use these outside the FORITFY_SOURCE implementation */ +#undef __underlying_memchr +#undef __underlying_memcmp +#undef __underlying_memcpy +#undef __underlying_memmove +#undef __underlying_memset +#undef __underlying_strcat +#undef __underlying_strcpy +#undef __underlying_strlen +#undef __underlying_strncat +#undef __underlying_strncpy #endif /** -- 2.20.1 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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 993ACC33CB1 for ; Thu, 16 Jan 2020 06:27:15 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0A6552075B for ; Thu, 16 Jan 2020 06:27:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Squ/PzDz"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=axtens.net header.i=@axtens.net header.b="Uhihq+6r" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0A6552075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=axtens.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=V98mWI7SXTZQvqSbAivwGGjn1SEuJZ2vojX4bZwfUrE=; b=Squ/PzDzKIHCJq cZ8wOEQ7KIBsjIkL53f3CbG3JH3a0bCfLVOkeA7rcPSIXdjTigQftnRG0wnJYgkEjCPTVaj+Ywi/O 82BiD33OS/ClOy4LlH09lf6SzX2H2yWQh0wn4F3WxlAMjDFzNJfbEub7dIGMyM/LFE84gAeZibet6 CWT90m3SBmst0U4PnGYPOB6k93dZLp9AmjUq5OVMrF6AD7vGXEKH6C3vVz6u9BsC2yx26IW2kymtb 5i/kwvqqIzsHcS+a5CDmhdKUnLP+GyPK0dtanzE2+ZIJPs9BT4TBugf1PHhACdVn4AimC3qRV5nav oLByvzRYzYYE0728h2vQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1irycT-0001i6-V0; Thu, 16 Jan 2020 06:27:05 +0000 Received: from mail-pl1-x642.google.com ([2607:f8b0:4864:20::642]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1iryc4-0001IS-If for linux-arm-kernel@lists.infradead.org; Thu, 16 Jan 2020 06:26:44 +0000 Received: by mail-pl1-x642.google.com with SMTP id b22so7885461pls.12 for ; Wed, 15 Jan 2020 22:26:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=axtens.net; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=ecViW2B6K6MgjtfxW3TT7mCoLEuRKAGSK4ebp685lGI=; b=Uhihq+6rfB5UyQl+9UDv+i3ThvZFs5H/8nw3PJ9UAbz3R2r3AMJzgomMFAzOXhQixb 9c4b8qrhyrPfdzEOkv05oUMvhz2JnmwO7kdW6N8LsZbFuuF4bvwkNyNZ4AOA+k+w3p4A vn7BPofvQmrLxHWpcX8lHyw7JZ1dUbkAXFCGQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=ecViW2B6K6MgjtfxW3TT7mCoLEuRKAGSK4ebp685lGI=; b=Syx9/L1s36qlRvAiJ8nz+ZvlckeV8igmrf2cguS+PGPxukeEyTgVf/mFkLc+xlLKQF NK7yp6P0DCj32C9iHjLTpiCwPm1hmqQqjA6fhDpp6uVGCBYkEmJzJeRmk6gKxhp9ozdN XJDcL44M/t52MpbSfZzbJ33cwJW5q4KF52fe3M1QtScFUAnCSio9U6pIswHrNfkC/B70 75CNBGx/E3ErGlMINdE8pQbF/Bo/sz/LUOW59NwyayqqN8Fo61AaCDNGUySwcaemtK3Y 1KJg43S5KxcqG59D+8V3OiMnIbTnd+J35z9i4d+q2253q0VGllFKCx8VvsQieDsN/Nbe e9Ow== X-Gm-Message-State: APjAAAVbI5U9a9q2puBx7YGCPfna1c90xrueL1eu4d+qy1ei0h15eb5C MIz6jgB3G/7kHcYw/fpt0P1v9A== X-Google-Smtp-Source: APXvYqw19UTxY8Hi9APh86aEtqUHLB8ch68t3FABEMRmpJHJbbxu4RZM4Mz69GnkzexI90XRmebJvQ== X-Received: by 2002:a17:90a:a608:: with SMTP id c8mr4785355pjq.36.1579155999384; Wed, 15 Jan 2020 22:26:39 -0800 (PST) Received: from localhost (2001-44b8-1113-6700-097c-7eed-afd4-cd15.static.ipv6.internode.on.net. [2001:44b8:1113:6700:97c:7eed:afd4:cd15]) by smtp.gmail.com with ESMTPSA id o16sm22735174pgl.58.2020.01.15.22.26.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Jan 2020 22:26:38 -0800 (PST) From: Daniel Axtens To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com Subject: [PATCH v2 2/3] string.h: fix incompatibility between FORTIFY_SOURCE and KASAN Date: Thu, 16 Jan 2020 17:26:24 +1100 Message-Id: <20200116062625.32692-3-dja@axtens.net> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20200116062625.32692-1-dja@axtens.net> References: <20200116062625.32692-1-dja@axtens.net> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200115_222640_676266_592C42CD X-CRM114-Status: GOOD ( 28.61 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: christophe.leroy@c-s.fr, linux-s390@vger.kernel.org, linux-xtensa@linux-xtensa.org, x86@kernel.org, Daniel Micay , Alexander Potapenko , linux-arm-kernel@lists.infradead.org, Andrey Ryabinin , linuxppc-dev@lists.ozlabs.org, dvyukov@google.com, Daniel Axtens Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org The memcmp KASAN self-test fails on a kernel with both KASAN and FORTIFY_SOURCE. 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. Using __builtins may bypass KASAN checks if the compiler decides to inline it's own implementation as sequence of instructions, rather than emit a function call that goes out to a KASAN-instrumented implementation. Why is only memcmp affected? ============================ Of the string and string-like functions that kasan_test tests, only memcmp is replaced by an inline sequence of instructions in my testing on x86 with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2). I believe this is due to compiler heuristics. For example, if I annotate kmalloc calls with the alloc_size annotation (and disable some fortify compile-time checking!), the compiler will replace every memset except the one in kmalloc_uaf_memset with inline instructions. (I have some WIP patches to add this annotation.) Does this affect other functions in string.h? ============================================= Yes. Anything that uses __builtin_* rather than __real_* could be affected. This looks like: - strncpy - strcat - strlen - strlcpy maybe, under some circumstances? - strncat under some circumstances - memset - memcpy - memmove - memcmp (as noted) - memchr - strcpy Whether a function call is emitted always depends on the compiler. Most bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows that this is not always the case. Isn't FORTIFY_SOURCE disabled with KASAN? ========================================- The string headers on all arches supporting KASAN disable fortify with kasan, but only when address sanitisation is _also_ disabled. For example from x86: #if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__) /* * For files that are not instrumented (e.g. mm/slub.c) we * should use not instrumented version of mem* functions. */ #define memcpy(dst, src, len) __memcpy(dst, src, len) #define memmove(dst, src, len) __memmove(dst, src, len) #define memset(s, c, n) __memset(s, c, n) #ifndef __NO_FORTIFY #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */ #endif #endif This comes from commit 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions"), and doesn't work when KASAN is enabled and the file is supposed to be sanitised - as with test_kasan.c I'm pretty sure this is not wrong, but not as expansive it should be: * we shouldn't use __builtin_memcpy etc in files where we don't have instrumentation - it could devolve into a function call to memcpy, which will be instrumented. Rather, we should use __memcpy which by convention is not instrumented. * we also shouldn't be using __builtin_memcpy when we have a KASAN instrumented file, because it could be replaced with inline asm that will not be instrumented. What is correct behaviour? ========================== Firstly, there is some overlap between fortification and KASAN: both provide some level of _runtime_ checking. Only fortify provides compile-time checking. KASAN and fortify can pick up different things at runtime: - Some fortify functions, notably the string functions, could easily be modified to consider sub-object sizes (e.g. members within a struct), and I have some WIP patches to do this. KASAN cannot detect these because it cannot insert poision between members of a struct. - KASAN can detect many over-reads/over-writes when the sizes of both operands are unknown, which fortify cannot. So there are a couple of options: 1) Flip the test: disable fortify in santised files and enable it in unsanitised files. This at least stops us missing KASAN checking, but we lose the fortify checking. 2) Make the fortify code always call out to real versions. Do this only for KASAN, for fear of losing the inlining opportunities we get from __builtin_*. (We can't use kasan_check_{read,write}: because the fortify functions are _extern inline_, you can't include _static_ inline functions without a compiler warning. kasan_check_{read,write} are static inline so we can't use them even when they would otherwise be suitable.) Take approach 2 and call out to real versions when KASAN is enabled. Use __underlying_foo to distinguish from __real_foo: __real_foo always refers to the kernel's implementation of foo, __underlying_foo could be either the kernel implementation or the __builtin_foo implementation. This is sometimes enough to make the memcmp test succeed with FORTIFY_SOURCE enabled. It is at least enough to get the function call into the module. One more fix is needed to make it reliable: see the next patch. Cc: Daniel Micay Cc: Andrey Ryabinin Cc: Alexander Potapenko Cc: Dmitry Vyukov Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions") Signed-off-by: Daniel Axtens --- v2: add #undefs, do not drop arch code: Dmitry pointed out that we _do_ want to disable fortify in non-sanitised files because of how __builtin_memcpy might end up as a call to regular memcpy rather than __memcpy. Dmitry, this might cause a few new syzkaller splats - I first picked it up building from a syskaller config. Or it might not, it just depends what gets replaced with an inline sequence of instructions. checkpatch complains about some over-long lines, happy to change the format if anyone has better ideas for how to lay it out. --- include/linux/string.h | 60 +++++++++++++++++++++++++++++++++--------- 1 file changed, 48 insertions(+), 12 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index 3b8e8b12dd37..18d3f7a4b2b9 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -317,6 +317,31 @@ void __read_overflow3(void) __compiletime_error("detected read beyond size of ob void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter"); #if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE) + +#ifdef CONFIG_KASAN +extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr); +extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp); +extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy); +extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove); +extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset); +extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat); +extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy); +extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen); +extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat); +extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy); +#else +#define __underlying_memchr __builtin_memchr +#define __underlying_memcmp __builtin_memcmp +#define __underlying_memcpy __builtin_memcpy +#define __underlying_memmove __builtin_memmove +#define __underlying_memset __builtin_memset +#define __underlying_strcat __builtin_strcat +#define __underlying_strcpy __builtin_strcpy +#define __underlying_strlen __builtin_strlen +#define __underlying_strncat __builtin_strncat +#define __underlying_strncpy __builtin_strncpy +#endif + __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) { size_t p_size = __builtin_object_size(p, 0); @@ -324,14 +349,14 @@ __FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size) __write_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_strncpy(p, q, size); + return __underlying_strncpy(p, q, size); } __FORTIFY_INLINE char *strcat(char *p, const char *q) { size_t p_size = __builtin_object_size(p, 0); if (p_size == (size_t)-1) - return __builtin_strcat(p, q); + return __underlying_strcat(p, q); if (strlcat(p, q, p_size) >= p_size) fortify_panic(__func__); return p; @@ -345,7 +370,7 @@ __FORTIFY_INLINE __kernel_size_t strlen(const char *p) /* Work around gcc excess stack consumption issue */ if (p_size == (size_t)-1 || (__builtin_constant_p(p[p_size - 1]) && p[p_size - 1] == '\0')) - return __builtin_strlen(p); + return __underlying_strlen(p); ret = strnlen(p, p_size); if (p_size <= ret) fortify_panic(__func__); @@ -378,7 +403,7 @@ __FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size) __write_overflow(); if (len >= p_size) fortify_panic(__func__); - __builtin_memcpy(p, q, len); + __underlying_memcpy(p, q, len); p[len] = '\0'; } return ret; @@ -391,12 +416,12 @@ __FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count) size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); if (p_size == (size_t)-1 && q_size == (size_t)-1) - return __builtin_strncat(p, q, count); + return __underlying_strncat(p, q, count); p_len = strlen(p); copy_len = strnlen(q, count); if (p_size < p_len + copy_len + 1) fortify_panic(__func__); - __builtin_memcpy(p + p_len, q, copy_len); + __underlying_memcpy(p + p_len, q, copy_len); p[p_len + copy_len] = '\0'; return p; } @@ -408,7 +433,7 @@ __FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size) __write_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_memset(p, c, size); + return __underlying_memset(p, c, size); } __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) @@ -423,7 +448,7 @@ __FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memcpy(p, q, size); + return __underlying_memcpy(p, q, size); } __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) @@ -438,7 +463,7 @@ __FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memmove(p, q, size); + return __underlying_memmove(p, q, size); } extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan); @@ -464,7 +489,7 @@ __FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size) } if (p_size < size || q_size < size) fortify_panic(__func__); - return __builtin_memcmp(p, q, size); + return __underlying_memcmp(p, q, size); } __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) @@ -474,7 +499,7 @@ __FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size) __read_overflow(); if (p_size < size) fortify_panic(__func__); - return __builtin_memchr(p, c, size); + return __underlying_memchr(p, c, size); } void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv); @@ -505,11 +530,22 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q) size_t p_size = __builtin_object_size(p, 0); size_t q_size = __builtin_object_size(q, 0); if (p_size == (size_t)-1 && q_size == (size_t)-1) - return __builtin_strcpy(p, q); + return __underlying_strcpy(p, q); memcpy(p, q, strlen(q) + 1); return p; } +/* Don't use these outside the FORITFY_SOURCE implementation */ +#undef __underlying_memchr +#undef __underlying_memcmp +#undef __underlying_memcpy +#undef __underlying_memmove +#undef __underlying_memset +#undef __underlying_strcat +#undef __underlying_strcpy +#undef __underlying_strlen +#undef __underlying_strncat +#undef __underlying_strncpy #endif /** -- 2.20.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel