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=-17.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,URIBL_BLOCKED,USER_AGENT_SANE_1 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 78966C11F64 for ; Mon, 28 Jun 2021 19:46:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 57DD461CA5 for ; Mon, 28 Jun 2021 19:46:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237098AbhF1Ts3 (ORCPT ); Mon, 28 Jun 2021 15:48:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:45000 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236432AbhF1Ts1 (ORCPT ); Mon, 28 Jun 2021 15:48:27 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CA4B061CA1; Mon, 28 Jun 2021 19:46:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624909562; bh=GIsAOsOlZwmkiVWrdlHO/oPzADy/yO9yVmM1KN/GG3g=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=jwf8DgqEM/Z/H3zx4e7zaIlwO9qfoBmyRLwzRXltJ9ttwzg6s9G9TE10Hp0MieXBU Rd96lYRUjfOA4U1pjDRHO/VDh+UbQQ1JNHdO+T04yMghZQfTwmFwTkSjN4AQ2H2Whp 8PusfVCYM2htMrYc/r7EOOjFRkGh+2C8hb1pMWx7vYZyZ076hX/evA0GaqGCr9UDGJ mCcPpKYWCOH/TKDuH4mTfOjCwlfmIY9VR7CHztvYnKZydiP6bIzwPPT1HeHPei6ApF Sy9mzIs9kwk215+3FkHYbFWPBEvQ4E1821+1TJCnwwhHhX1LfOFc6oPvZs/uqjhEgt wD4vb0JWvyPTw== Subject: Re: [PATCH v2] kallsyms: strip LTO suffixes from static functions To: Nick Desaulniers , Kees Cook Cc: Fangrui Song , "KE . LI" , Andrew Morton , Stephen Rothwell , Miroslav Benes , Jessica Yu , Joe Perches , "Gustavo A. R. Silva" , Sami Tolvanen , Randy Dunlap , Stephen Boyd , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com References: <20210622201822.ayavok3d2fw3u2pl@google.com> <20210628190509.2486992-1-ndesaulniers@google.com> From: Nathan Chancellor Message-ID: Date: Mon, 28 Jun 2021 12:45:59 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210628190509.2486992-1-ndesaulniers@google.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/28/2021 12:05 PM, 'Nick Desaulniers' via Clang Built Linux wrote: > Similar to: > commit 8b8e6b5d3b01 ("kallsyms: strip ThinLTO hashes from static > functions") > > It's very common for compilers to modify the symbol name for static > functions as part of optimizing transformations. That makes hooking > static functions (that weren't inlined or DCE'd) with kprobes difficult. > > LLVM has yet another name mangling scheme used by thin LTO. Strip off > these suffixes so that we can continue to hook such static functions. > > Reported-by: KE.LI(Lieke) > Signed-off-by: Nick Desaulniers > --- > Changes v1 -> v2: > * Both mangling schemes can occur for thinLTO + CFI, this new scheme can > also occur for thinLTO without CFI. Split cleanup_symbol_name() into > two function calls. > * Drop KE.LI's tested by tag. > * Do not carry Fangrui's Reviewed by tag. > * Drop the inline keyword; it is meaningless. > > kernel/kallsyms.c | 33 +++++++++++++++++++++++++++++---- > 1 file changed, 29 insertions(+), 4 deletions(-) > > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c > index 4067564ec59f..fbce4a1ec700 100644 > --- a/kernel/kallsyms.c > +++ b/kernel/kallsyms.c > @@ -171,14 +171,30 @@ static unsigned long kallsyms_sym_address(int idx) > return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; > } > > -#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN) > +#ifdef CONFIG_LTO_CLANG_THIN > +/* > + * LLVM appends a suffix for local variables that must be promoted to global > + * scope as part of thin LTO. foo() becomes foo.llvm.974640843467629774. This > + * can break hooking of static functions with kprobes. > + */ > +static bool cleanup_symbol_name_thinlto(char *s) > +{ > + char *res; > + > + res = strstr(s, ".llvm."); > + if (res) > + *res = '\0'; > + > + return res != NULL; > +} > +#ifdef CONFIG_CFI_CLANG > /* > * LLVM appends a hash to static function names when ThinLTO and CFI are > * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b. > * This causes confusion and potentially breaks user space tools, so we > * strip the suffix from expanded symbol names. > */ > -static inline bool cleanup_symbol_name(char *s) > +static bool cleanup_symbol_name_thinlto_cfi(char *s) > { > char *res; > > @@ -189,8 +205,17 @@ static inline bool cleanup_symbol_name(char *s) > return res != NULL; > } > #else > -static inline bool cleanup_symbol_name(char *s) { return false; } > -#endif > +static bool cleanup_symbol_name_thinlto_cfi(char *s) { return false; } > +#endif /* CONFIG_CFI_CLANG */ > +#else > +static bool cleanup_symbol_name_thinlto(char *s) { return false; } > +#endif /* CONFIG_LTO_CLANG_THIN */ > + > +static bool cleanup_symbol_name(char *s) > +{ > + return cleanup_symbol_name_thinlto(s) && > + cleanup_symbol_name_thinlto_cfi(s); Won't this be a build error when CONFIG_LTO_CLANG_THIN=n and CONFIG_CFI_CLANG=n because cleanup_symbol_name_thinlto_cfi() will not be defined? Should the cleanup_symbol_name_thinlto_cfi() stub be in the last else block? Cheers, Nathan > +} > > /* Lookup the address for this symbol. Returns 0 if not found. */ > unsigned long kallsyms_lookup_name(const char *name) >