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=-16.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 DA2AAC433DB for ; Wed, 10 Feb 2021 05:18:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 74F4664E56 for ; Wed, 10 Feb 2021 05:18:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 74F4664E56 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 11F726B0073; Wed, 10 Feb 2021 00:18:35 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0F7026B0074; Wed, 10 Feb 2021 00:18:35 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E155B8D0001; Wed, 10 Feb 2021 00:18:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0126.hostedemail.com [216.40.44.126]) by kanga.kvack.org (Postfix) with ESMTP id CC25E6B0073 for ; Wed, 10 Feb 2021 00:18:34 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 9C36D8248076 for ; Wed, 10 Feb 2021 05:18:34 +0000 (UTC) X-FDA: 77801202948.04.music27_4c16d1c2760d Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin04.hostedemail.com (Postfix) with ESMTP id 84B998045FB9 for ; Wed, 10 Feb 2021 05:18:34 +0000 (UTC) X-HE-Tag: music27_4c16d1c2760d X-Filterd-Recvd-Size: 7261 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Wed, 10 Feb 2021 05:18:33 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 5E59464E45; Wed, 10 Feb 2021 05:18:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612934313; bh=V5tnoziY2hMH/8D5UdgC5pB8GP//YpSeQXh/fPdcfMg=; h=From:To:Subject:Date:In-Reply-To:References:From; b=G5+MQtyLVJ4v/LNssd7nAFVCymdSi+QU/n68hkrUFBoYkTUSsS8i4iO3pOQ2qwL6i 31A8/E+qR+5M+MlfNzmYWTlIc+gXTmRTcDw+9fpRjpwlW0pPdZl9+xZ20QxJRxLZG2 pdacZbioJnRVcq8r2EbKQSYKokHMx5GQZapiLYYuH00n/LrTPm/1pAjqLmEV64cZZi 26PgvlLCOzskmzmwrip2JmcCZiPv4KKZ9EY6pMjG23gRxidIADVQxG/5YjAqFxW36U tyZBb3yrIXUfL+OaYQKBI7A096qzxfj4/XKWkrLmwh2Rd4EK0PLWDCHis3Z6yVZjT7 x6i+sAoqpIFOQ== From: Timur Tabi To: Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Vlastimil Babka , Andy Shevchenko , Matthew Wilcox , akpm@linux-foundation.org, Linus Torvalds , roman.fietze@magna.com, Kees Cook , John Ogness , akinobu.mita@gmail.com, glider@google.com, Andrey Konovalov , Marco Elver , Rasmus Villemoes , Pavel Machek , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 3/3] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed Date: Tue, 9 Feb 2021 23:18:14 -0600 Message-Id: <20210210051814.845713-4-timur@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210210051814.845713-1-timur@kernel.org> References: <20210210051814.845713-1-timur@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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: If the make-printk-non-secret command line parameter is set, then printk("%p") will print pointers as unhashed. This is useful for debugging purposes. A large warning message is displayed if this option is enabled. Unhashed pointers, while useful for debugging, expose kernel addresses which can be a security risk. Also update test_printf to skip the hashed pointer tests if the command-line option is set. Signed-off-by: Timur Tabi Acked-by: Petr Mladek Acked-by: Randy Dunlap Acked-by: Sergey Senozhatsky --- .../admin-guide/kernel-parameters.txt | 15 ++++++++ lib/test_printf.c | 8 ++++ lib/vsprintf.c | 38 ++++++++++++++++++- 3 files changed, 59 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentat= ion/admin-guide/kernel-parameters.txt index a10b545c2070..6962379469e4 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2613,6 +2613,21 @@ different yeeloong laptops. Example: machtype=3Dlemote-yeeloong-2f-7inch =20 + make-printk-non-secret + Force pointers printed to the console to be unhashed. + By default, when a pointer is printed to the kernel + console (via %p format string), that pointer is + "hashed", i.e. obscured by hashing the pointer value. + This is a security feature that hides actual kernel + addresses from unprivileged users, but it also makes + debugging the kernel more difficult since unequal + pointers can no longer be compared. If this option is + specified, then all normal pointers will have their + true value printed. Pointers printed via %pK may + still be hashed. This option should only be specified + when debugging the kernel. Please do not use on + production kernels. + max_addr=3Dnn[KMG] [KNL,BOOT,ia64] All physical memory greater than or equal to this physical address is ignored. =20 diff --git a/lib/test_printf.c b/lib/test_printf.c index ad2bcfa8caa1..b0b62d76e598 100644 --- a/lib/test_printf.c +++ b/lib/test_printf.c @@ -35,6 +35,8 @@ KSTM_MODULE_GLOBALS(); static char *test_buffer __initdata; static char *alloced_buffer __initdata; =20 +extern bool debug_never_hash_pointers; + static int __printf(4, 0) __init do_test(int bufsize, const char *expect, int elen, const char *fmt, va_list ap) @@ -301,6 +303,12 @@ plain(void) { int err; =20 + if (debug_never_hash_pointers) { + pr_warn("skipping plain 'p' tests"); + skipped_tests +=3D 2; + return; + } + err =3D plain_hash(); if (err) { pr_warn("plain 'p' does not appear to be hashed\n"); diff --git a/lib/vsprintf.c b/lib/vsprintf.c index 3b53c73580c5..1296d9b0b328 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -2090,6 +2090,34 @@ char *fwnode_string(char *buf, char *end, struct f= wnode_handle *fwnode, return widen_string(buf, buf - buf_start, end, spec); } =20 +/* Disable pointer hashing if requested */ +bool debug_never_hash_pointers __ro_after_init; +EXPORT_SYMBOL_GPL(debug_never_hash_pointers); + +static int __init debug_never_hash_pointers_enable(char *str) +{ + debug_never_hash_pointers =3D true; + + pr_warn("**********************************************************\n")= ; + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n")= ; + pr_warn("** **\n")= ; + pr_warn("** All pointers that are printed to the console will **\n")= ; + pr_warn("** be printed as unhashed. **\n")= ; + pr_warn("** **\n")= ; + pr_warn("** Kernel memory addresses are exposed, which may **\n")= ; + pr_warn("** reduce the security of your system. **\n")= ; + pr_warn("** **\n")= ; + pr_warn("** If you see this message and you are not debugging **\n")= ; + pr_warn("** the kernel, report this immediately to your system **\n")= ; + pr_warn("** administrator! **\n")= ; + pr_warn("** **\n")= ; + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n")= ; + pr_warn("**********************************************************\n")= ; + + return 0; +} +early_param("make-printk-non-secret", debug_never_hash_pointers_enable); + /* * Show a '%p' thing. A kernel extension is that the '%p' is followed * by an extra set of alphanumeric characters that are extended format @@ -2297,8 +2325,14 @@ char *pointer(const char *fmt, char *buf, char *en= d, void *ptr, } } =20 - /* default is to _not_ leak addresses, hash before printing */ - return ptr_to_id(buf, end, ptr, spec); + /* + * default is to _not_ leak addresses, so hash before printing unless + * make-printk-non-secret is specified on the command line. + */ + if (unlikely(debug_never_hash_pointers)) + return pointer_string(buf, end, ptr, spec); + else + return ptr_to_id(buf, end, ptr, spec); } =20 /* --=20 2.25.1