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 870FAC43217 for ; Wed, 9 Feb 2022 19:02:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241622AbiBITBx (ORCPT ); Wed, 9 Feb 2022 14:01:53 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34194 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241982AbiBITAp (ORCPT ); Wed, 9 Feb 2022 14:00:45 -0500 Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 411E5C03C19D; Wed, 9 Feb 2022 11:00:36 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1644433236; x=1675969236; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=3TFoJ8hml7DfFEwN1MeCftGLxN9fAc0FL9jRFOXIT44=; b=iY3BbgsG9rBd08M2OkWr5HiRdpN7sRL89OQ1Ycj1kYMbTokO//Hg/bi8 djm+x+5+OjUKdZRfKLbFvBc0kh5JgcEy7tRBREWCZtuwkR+vBQiRaNGVX mGZ4RX7egvS6AXw4tBwFz60XQDz2BHubi3dTsG3MmfpIXlE9MT8N7UtEI gNYgdAToX77bcTcogrdS2SUuXFMGPx0GOcoStgqujJr69rG1+hE3AMlqi Peg6lPrGmthtRR0ajHb8je/7QkUtIxNfVbbEcSriSTHB5kAaCkZxH4YuA dS1Yu/mClY9RB4E2gPPi6OTk1dCWcutj6bGsMiFxHqiNfLcdjQ+uO5z0G A==; X-IronPort-AV: E=McAfee;i="6200,9189,10253"; a="232869378" X-IronPort-AV: E=Sophos;i="5.88,356,1635231600"; d="scan'208";a="232869378" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Feb 2022 10:59:04 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.88,356,1635231600"; d="scan'208";a="541248491" Received: from irvmail001.ir.intel.com ([10.43.11.63]) by orsmga008.jf.intel.com with ESMTP; 09 Feb 2022 10:58:52 -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 219IwjQP031082; Wed, 9 Feb 2022 18:58:50 GMT From: Alexander Lobakin To: linux-hardening@vger.kernel.org, x86@kernel.org Cc: Alexander Lobakin , Borislav Petkov , 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 , Christoph Hellwig , Dave Hansen , "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Arnd Bergmann , Josh Poimboeuf , Nathan Chancellor , Masami Hiramatsu , Marios Pomonis , Sami Tolvanen , "H.J. Lu" , Nicolas Pitre , 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 v10 02/15] livepatch: avoid position-based search if `-z unique-symbol` is available Date: Wed, 9 Feb 2022 19:57:39 +0100 Message-Id: <20220209185752.1226407-3-alexandr.lobakin@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220209185752.1226407-1-alexandr.lobakin@intel.com> References: <20220209185752.1226407-1-alexandr.lobakin@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org Position-based search, which means that if there are several symbols with the same name, the user needs to additionally provide the "index" of a desired symbol, is fragile. For example, it breaks when two symbols with the same name are located in different sections. Since a while, LD has a flag `-z unique-symbol` which appends numeric suffixes to the functions with the same name (in symtab and strtab). It can be used to effectively prevent from having any ambiguity when referring to a symbol by its name. Check for its availability and always prefer when the livepatching is on. It can be used unconditionally later on after broader testing on a wide variety of machines, but for now let's stick to the actual CONFIG_LIVEPATCH=y case, which is true for most of distro configs anyways. This needs a little adjustment to the modpost to make it strip suffixes before adding exports. depmod needs some treatment as well, tho its false-positive warnings about unknown symbols are harmless and don't alter the return code. There is probably a bunch more livepatch code to optimize-out after introducing this, leave it for later as well. Suggested-by: H.J. Lu Suggested-by: Peter Zijlstra Suggested-by: Josh Poimboeuf Suggested-by: Miroslav Benes Signed-off-by: Alexander Lobakin --- Makefile | 6 ++++++ init/Kconfig | 3 +++ kernel/livepatch/core.c | 17 +++++++++++++---- scripts/mod/modpost.c | 42 ++++++++++++++++++++++------------------- 4 files changed, 45 insertions(+), 23 deletions(-) diff --git a/Makefile b/Makefile index ceb987e5c87b..fa9f947c9839 100644 --- a/Makefile +++ b/Makefile @@ -871,6 +871,12 @@ ifdef CONFIG_DEBUG_SECTION_MISMATCH KBUILD_CFLAGS += -fno-inline-functions-called-once endif +# Prefer linking with the `-z unique-symbol` if available, this eliminates +# position-based search +ifeq ($(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL)$(CONFIG_LIVEPATCH),yy) +KBUILD_LDFLAGS += -z unique-symbol +endif + ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION KBUILD_CFLAGS_KERNEL += -ffunction-sections -fdata-sections LDFLAGS_vmlinux += --gc-sections diff --git a/init/Kconfig b/init/Kconfig index e9119bf54b1f..8e900d17d42b 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -86,6 +86,9 @@ config CC_HAS_ASM_INLINE config CC_HAS_NO_PROFILE_FN_ATTR def_bool $(success,echo '__attribute__((no_profile_instrument_function)) int x();' | $(CC) -x c - -c -o /dev/null -Werror) +config LD_HAS_Z_UNIQUE_SYMBOL + def_bool $(ld-option,-z unique-symbol) + config CONSTRUCTORS bool diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index 585494ec464f..7a330465a8c7 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -143,11 +143,13 @@ static int klp_find_callback(void *data, const char *name, args->count++; /* - * Finish the search when the symbol is found for the desired position - * or the position is not defined for a non-unique symbol. + * Finish the search when unique symbol names are enabled + * or the symbol is found for the desired position or the + * position is not defined for a non-unique symbol. */ - if ((args->pos && (args->count == args->pos)) || - (!args->pos && (args->count > 1))) + if (IS_ENABLED(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL) || + (args->pos && args->count == args->pos) || + (!args->pos && args->count > 1)) return 1; return 0; @@ -169,6 +171,13 @@ static int klp_find_object_symbol(const char *objname, const char *name, else kallsyms_on_each_symbol(klp_find_callback, &args); + /* + * If the LD's `-z unique-symbol` flag is available and enabled, + * sympos checks are not relevant. + */ + if (IS_ENABLED(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL)) + sympos = 0; + /* * Ensure an address was found. If sympos is 0, ensure symbol is unique; * otherwise ensure the symbol position count matches sympos. diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c index 4648b7afe5cc..ec521ccebea6 100644 --- a/scripts/mod/modpost.c +++ b/scripts/mod/modpost.c @@ -689,11 +689,28 @@ static void handle_modversion(const struct module *mod, sym_set_crc(symname, crc); } +static char *remove_dot(char *s) +{ + size_t n = strcspn(s, "."); + + if (n && s[n]) { + size_t m = strspn(s + n + 1, "0123456789"); + + if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0)) + s[n] = 0; + + /* strip trailing .lto */ + if (strends(s, ".lto")) + s[strlen(s) - 4] = '\0'; + } + + return s; +} + static void handle_symbol(struct module *mod, struct elf_info *info, const Elf_Sym *sym, const char *symname) { enum export export; - const char *name; if (strstarts(symname, "__ksymtab")) export = export_from_secname(info, get_secindex(info, sym)); @@ -734,8 +751,11 @@ static void handle_symbol(struct module *mod, struct elf_info *info, default: /* All exported symbols */ if (strstarts(symname, "__ksymtab_")) { - name = symname + strlen("__ksymtab_"); - sym_add_exported(name, mod, export); + char *name; + + name = NOFAIL(strdup(symname + strlen("__ksymtab_"))); + sym_add_exported(remove_dot(name), mod, export); + free(name); } if (strcmp(symname, "init_module") == 0) mod->has_init = 1; @@ -1980,22 +2000,6 @@ static void check_sec_ref(struct module *mod, const char *modname, } } -static char *remove_dot(char *s) -{ - size_t n = strcspn(s, "."); - - if (n && s[n]) { - size_t m = strspn(s + n + 1, "0123456789"); - if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0)) - s[n] = 0; - - /* strip trailing .lto */ - if (strends(s, ".lto")) - s[strlen(s) - 4] = '\0'; - } - return s; -} - static void read_symbols(const char *modname) { const char *symname; -- 2.34.1