From patchwork Thu Dec 2 22:32:07 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alexander Lobakin X-Patchwork-Id: 12653687 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 D8E29C43217 for ; Thu, 2 Dec 2021 22:33:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349730AbhLBWgr (ORCPT ); Thu, 2 Dec 2021 17:36:47 -0500 Received: from mga03.intel.com ([134.134.136.65]:52308 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245276AbhLBWgg (ORCPT ); Thu, 2 Dec 2021 17:36:36 -0500 X-IronPort-AV: E=McAfee;i="6200,9189,10186"; a="236795822" X-IronPort-AV: E=Sophos;i="5.87,282,1631602800"; d="scan'208";a="236795822" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Dec 2021 14:33:12 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.87,282,1631602800"; d="scan'208";a="459836417" Received: from irvmail001.ir.intel.com ([10.43.11.63]) by orsmga003.jf.intel.com with ESMTP; 02 Dec 2021 14:33:04 -0800 Received: from newjersey.igk.intel.com (newjersey.igk.intel.com [10.102.20.203]) by irvmail001.ir.intel.com (8.14.3/8.13.6/MailSET/Hub) with ESMTP id 1B2MWmYY028552; Thu, 2 Dec 2021 22:33:01 GMT From: Alexander Lobakin To: linux-hardening@vger.kernel.org, x86@kernel.org Cc: Alexander Lobakin , Jesse Brandeburg , Kristen Carlson Accardi , Kees Cook , Miklos Szeredi , Ard Biesheuvel , Tony Luck , Bruce Schlobohm , Jessica Yu , kernel test robot , Miroslav Benes , Evgenii Shatokhin , Jonathan Corbet , Masahiro Yamada , Michal Marek , Nick Desaulniers , Herbert Xu , "David S. Miller" , Thomas Gleixner , Will Deacon , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnd Bergmann , Josh Poimboeuf , Nathan Chancellor , Masami Hiramatsu , Marios Pomonis , Sami Tolvanen , linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-arch@vger.kernel.org, live-patching@vger.kernel.org, llvm@lists.linux.dev Subject: [PATCH v8 07/14] kallsyms: Hide layout Date: Thu, 2 Dec 2021 23:32:07 +0100 Message-Id: <20211202223214.72888-8-alexandr.lobakin@intel.com> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20211202223214.72888-1-alexandr.lobakin@intel.com> References: <20211202223214.72888-1-alexandr.lobakin@intel.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org From: Kristen Carlson Accardi This patch makes /proc/kallsyms display in a random order, rather than sorted by address in order to hide the newly randomized address layout. Signed-off-by: Kristen Carlson Accardi Reviewed-by: Tony Luck Tested-by: Tony Luck Reported-by: kernel test robot # swap.cocci Signed-off-by: Alexander Lobakin --- kernel/kallsyms.c | 158 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 157 insertions(+), 1 deletion(-) diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 3011bc33a5ba..ff9d8b651966 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -583,6 +583,12 @@ struct kallsym_iter { int show_value; }; +struct kallsyms_shuffled_iter { + struct kallsym_iter iter; + loff_t total_syms; + loff_t shuffled_index[]; +}; + int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value, char *type, char *name) { @@ -830,7 +836,7 @@ bool kallsyms_show_value(const struct cred *cred) } } -static int kallsyms_open(struct inode *inode, struct file *file) +static int __kallsyms_open(struct inode *inode, struct file *file) { /* * We keep iterator in m->private, since normal case is to @@ -851,6 +857,156 @@ static int kallsyms_open(struct inode *inode, struct file *file) return 0; } +/* + * When function granular kaslr is enabled, we need to print out the symbols + * at random so we don't reveal the new layout. + */ +#ifdef CONFIG_FG_KASLR +static int update_random_pos(struct kallsyms_shuffled_iter *s_iter, + loff_t pos, loff_t *new_pos) +{ + loff_t new; + + if (pos >= s_iter->total_syms) + return 0; + + new = s_iter->shuffled_index[pos]; + + /* + * normally this would be done as part of update_iter, however, + * we want to avoid triggering this in the event that new is + * zero since we don't want to blow away our pos end indicators. + */ + if (new == 0) { + s_iter->iter.name[0] = '\0'; + s_iter->iter.nameoff = get_symbol_offset(new); + s_iter->iter.pos = new; + } + + *new_pos = new; + return 1; +} + +static void *shuffled_start(struct seq_file *m, loff_t *pos) +{ + struct kallsyms_shuffled_iter *s_iter = m->private; + loff_t new_pos; + + if (!update_random_pos(s_iter, *pos, &new_pos)) + return NULL; + + return s_start(m, &new_pos); +} + +static void *shuffled_next(struct seq_file *m, void *p, loff_t *pos) +{ + struct kallsyms_shuffled_iter *s_iter = m->private; + loff_t new_pos; + + (*pos)++; + + if (!update_random_pos(s_iter, *pos, &new_pos)) + return NULL; + + if (!update_iter(m->private, new_pos)) + return NULL; + + return p; +} + +/* + * shuffle_index_list() + * Use a Fisher Yates algorithm to shuffle a list of text sections. + */ +static void shuffle_index_list(loff_t *indexes, loff_t size) +{ + u32 i, j; + + for (i = size - 1; i > 0; i--) { + /* pick a random index from 0 to i */ + j = get_random_u32() % (i + 1); + + swap(indexes[i], indexes[j]); + } +} + +static const struct seq_operations kallsyms_shuffled_op = { + .start = shuffled_start, + .next = shuffled_next, + .stop = s_stop, + .show = s_show +}; + +static int kallsyms_random_open(struct inode *inode, struct file *file) +{ + loff_t pos; + struct kallsyms_shuffled_iter *shuffled_iter; + struct kallsym_iter iter; + bool show_value; + + /* + * If privileged, go ahead and use the normal algorithm for + * displaying symbols + */ + show_value = kallsyms_show_value(file->f_cred); + if (show_value) + return __kallsyms_open(inode, file); + + /* + * we need to figure out how many extra symbols there are + * to print out past kallsyms_num_syms + */ + pos = kallsyms_num_syms; + reset_iter(&iter, 0); + do { + if (!update_iter(&iter, pos)) + break; + pos++; + } while (1); + + /* + * add storage space for an array of loff_t equal to the size + * of the total number of symbols we need to print + */ + shuffled_iter = __seq_open_private(file, &kallsyms_shuffled_op, + sizeof(*shuffled_iter) + + (sizeof(pos) * pos)); + if (!shuffled_iter) + return -ENOMEM; + + reset_iter(&shuffled_iter->iter, 0); + shuffled_iter->iter.show_value = show_value; + shuffled_iter->total_syms = pos; + + /* + * the existing update_iter algorithm requires that we + * are either moving along increasing pos sequentially, + * or that these values are correct. Since these values + * were discovered above, initialize our new iter so we + * can use update_iter non-sequentially. + */ + shuffled_iter->iter.pos_arch_end = iter.pos_arch_end; + shuffled_iter->iter.pos_mod_end = iter.pos_mod_end; + shuffled_iter->iter.pos_ftrace_mod_end = iter.pos_ftrace_mod_end; + + /* + * initialize the array with all possible pos values, then + * shuffle the array so that the values will display in a random + * order. + */ + for (pos = 0; pos < shuffled_iter->total_syms; pos++) + shuffled_iter->shuffled_index[pos] = pos; + + shuffle_index_list(shuffled_iter->shuffled_index, shuffled_iter->total_syms); + + return 0; +} + +#define kallsyms_open kallsyms_random_open +#else +#define kallsyms_open __kallsyms_open +#endif /* !CONFIG_FG_KASLR */ + #ifdef CONFIG_KGDB_KDB const char *kdb_walk_kallsyms(loff_t *pos) {