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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5DFCDC4321E for ; Sun, 9 Oct 2022 20:54:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230129AbiJIUyf (ORCPT ); Sun, 9 Oct 2022 16:54:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44960 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230310AbiJIUxh (ORCPT ); Sun, 9 Oct 2022 16:53:37 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AA4C830557; Sun, 9 Oct 2022 13:52:41 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id DAA47B80DC4; Sun, 9 Oct 2022 20:52:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 090B9C433D6; Sun, 9 Oct 2022 20:52:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1665348758; bh=hzbiDCjgP4PWpxtEpRK2mCWbxYUpFdc6paCISbBKNxg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=VPmd5hluPJe5Mjr6czZ3IznGYFbRVwrIKDmKnxVxc23tY4G7sGy1WW3Qiw+KzZSex n2NAmDA97sZkqAUhcs69JZx3A4m7AQN9lfxGCVQKp6HhbDBl1cJuqXlsOkQBzWHtOl MT8uP4LjnKH5ZJpDQ/6devxq24ipNwOAnzeGCF6+1Nrvd9Hu7C03I/7C16pBYUwV3o zDvN2r7MT6gbN156fgW9ZgQHTvB/GD+NDy+VrAxxdb59Y3VRgP5BZHBBU2MxDE2gCd 0DLQ+LCt1Wsbw9yQdJbLuyMIQmVHV7nkE0zQGJsUeoYL4fxyT81hKNwo98tazDyn5b qT7MU4Bho0RGQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Kees Cook , Nathan Chancellor , Tom Rix , Andrew Morton , Vlastimil Babka , "Steven Rostedt (Google)" , David Gow , Yury Norov , Masami Hiramatsu , Sander Vanheule , linux-hardening@vger.kernel.org, llvm@lists.linux.dev, Nick Desaulniers , Sasha Levin Subject: [PATCH AUTOSEL 5.19 06/16] fortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL Date: Sun, 9 Oct 2022 16:52:15 -0400 Message-Id: <20221009205226.1202133-6-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221009205226.1202133-1-sashal@kernel.org> References: <20221009205226.1202133-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kees Cook [ Upstream commit d07c0acb4f41cc42a0d97530946965b3e4fa68c1 ] With CONFIG_FORTIFY=y and CONFIG_UBSAN_LOCAL_BOUNDS=y enabled, we observe a runtime panic while running Android's Compatibility Test Suite's (CTS) android.hardware.input.cts.tests. This is stemming from a strlen() call in hidinput_allocate(). __compiletime_strlen() is implemented in terms of __builtin_object_size(), then does an array access to check for NUL-termination. A quirk of __builtin_object_size() is that for strings whose values are runtime dependent, __builtin_object_size(str, 1 or 0) returns the maximum size of possible values when those sizes are determinable at compile time. Example: static const char *v = "FOO BAR"; static const char *y = "FOO BA"; unsigned long x (int z) { // Returns 8, which is: // max(__builtin_object_size(v, 1), __builtin_object_size(y, 1)) return __builtin_object_size(z ? v : y, 1); } So when FORTIFY_SOURCE is enabled, the current implementation of __compiletime_strlen() will try to access beyond the end of y at runtime using the size of v. Mixed with UBSAN_LOCAL_BOUNDS we get a fault. hidinput_allocate() has a local C string whose value is control flow dependent on a switch statement, so __builtin_object_size(str, 1) evaluates to the maximum string length, making all other cases fault on the last character check. hidinput_allocate() could be cleaned up to avoid runtime calls to strlen() since the local variable can only have literal values, so there's no benefit to trying to fortify the strlen call site there. Perform a __builtin_constant_p() check against index 0 earlier in the macro to filter out the control-flow-dependant case. Add a KUnit test for checking the expected behavioral characteristics of FORTIFY_SOURCE internals. Cc: Nathan Chancellor Cc: Tom Rix Cc: Andrew Morton Cc: Vlastimil Babka Cc: "Steven Rostedt (Google)" Cc: David Gow Cc: Yury Norov Cc: Masami Hiramatsu Cc: Sander Vanheule Cc: linux-hardening@vger.kernel.org Cc: llvm@lists.linux.dev Reviewed-by: Nick Desaulniers Tested-by: Android Treehugger Robot Link: https://android-review.googlesource.com/c/kernel/common/+/2206839 Co-developed-by: Nick Desaulniers Signed-off-by: Nick Desaulniers Signed-off-by: Kees Cook Signed-off-by: Sasha Levin --- include/linux/fortify-string.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index 3b401fa0f374..fce2fb2fc962 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -19,7 +19,8 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning(" unsigned char *__p = (unsigned char *)(p); \ size_t __ret = (size_t)-1; \ size_t __p_size = __builtin_object_size(p, 1); \ - if (__p_size != (size_t)-1) { \ + if (__p_size != (size_t)-1 && \ + __builtin_constant_p(*__p)) { \ size_t __p_len = __p_size - 1; \ if (__builtin_constant_p(__p[__p_len]) && \ __p[__p_len] == '\0') \ -- 2.35.1