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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 B13A5C11F64 for ; Mon, 28 Jun 2021 21:20:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9429B61CF9 for ; Mon, 28 Jun 2021 21:20:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236995AbhF1VWf (ORCPT ); Mon, 28 Jun 2021 17:22:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:35390 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233305AbhF1VWX (ORCPT ); Mon, 28 Jun 2021 17:22:23 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 6AF0661CF1; Mon, 28 Jun 2021 21:19:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624915197; bh=JLgA83Go9kNBblh6xu8yREwWPanuBbL0eeKHdxt1AyY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CwXXvT+2Vazdq7oS8qjSrQfXxM7sPZpW7kw2UrU+thxrWfRw762qwB5FOLOTuCQeL vAhvDuL5GMP0SZ+boEOmMul9XQcpQ0GUXv6NG9eVF+VWYNDoVy7RSQTKPF2QzLRGjF lN4IlMrvFTTcsX6xzyPoUIuMuUdzcEW+RXPTk3CvYqG+l1/ZN+OoKgnbqtUgBm/MeA rMztQmnu1lcfy4wi40nkOn0+Yh5+OJrWGcXHbj4um7xri7rkTvEvAz0nA2l463Tm4A j/9IM18Tnf3iadLbF410Om+liwWfUoGkEK8FFvDBZ32FRtvaOp5rsFTcdiEMsMGVNh mNnAEO4RT0qfg== Date: Mon, 28 Jun 2021 14:19:52 -0700 From: Nathan Chancellor To: Nick Desaulniers Cc: Kees Cook , Fangrui Song , "KE . LI" , Andrew Morton , Stephen Rothwell , Miguel Ojeda , Joe Perches , "Gustavo A. R. Silva" , Randy Dunlap , Sami Tolvanen , Stephen Boyd , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com Subject: Re: [PATCH v3] kallsyms: strip LTO suffixes from static functions Message-ID: References: <20210628203109.2501792-1-ndesaulniers@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210628203109.2501792-1-ndesaulniers@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 28, 2021 at 01:31:06PM -0700, Nick Desaulniers 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 v2 -> V3: > * Un-nest preprocessor checks, as per Nathan. > > 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 | 32 +++++++++++++++++++++++++++++--- > 1 file changed, 29 insertions(+), 3 deletions(-) > > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c > index 4067564ec59f..143c69e7e75d 100644 > --- a/kernel/kallsyms.c > +++ b/kernel/kallsyms.c > @@ -171,6 +171,26 @@ static unsigned long kallsyms_sym_address(int idx) > return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; > } > > +#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; > +} > +#else > +static bool cleanup_symbol_name_thinlto(char *s) { return false; } > +#endif /* CONFIG_LTO_CLANG_THIN */ > + > #if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN) > /* > * LLVM appends a hash to static function names when ThinLTO and CFI are > @@ -178,7 +198,7 @@ static unsigned long kallsyms_sym_address(int idx) > * 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 +209,14 @@ 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 && CONFIG_LTO_CLANG_THIN */ > + > +static bool cleanup_symbol_name(char *s) > +{ > + return cleanup_symbol_name_thinlto(s) && > + cleanup_symbol_name_thinlto_cfi(s); > +} > > /* Lookup the address for this symbol. Returns 0 if not found. */ > unsigned long kallsyms_lookup_name(const char *name) > -- > 2.32.0.93.g670b81a890-goog > Is there any reason that we cannot eliminate the stubs and combine the functions, or am I missing something? Completely untested diff. diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index c851ca0ed357..014b59ad68a3 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -161,26 +161,36 @@ 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) -/* - * LLVM appends a hash to static function names when ThinLTO and CFI are - * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b. - * This causes confusion and potentially breaks user space tools, so we - * strip the suffix from expanded symbol names. - */ -static inline bool cleanup_symbol_name(char *s) +static inline bool cleanup_symbol_name_thinlto(char *s) { char *res; - res = strrchr(s, '$'); + if (!IS_ENABLED(CONFIG_LTO_CLANG_THIN)) + return false; + + /* + * LLVM appends a suffix for local variables that must be promoted to global + * scope as part of ThinLTO. foo() becomes foo.llvm.974640843467629774. This + * can break hooking of static functions with kprobes. + */ + res = strstr(s, ".llvm."); if (res) *res = '\0'; + /* + * LLVM appends a hash to static function names when ThinLTO and CFI are + * both enabled, i.e. foo() becomes foo$707af9a22804d33c81801f27dcfe489b. + * This causes confusion and potentially breaks user space tools, so we + * strip the suffix from expanded symbol names. + */ + if (IS_ENABLED(CONFIG_CFI_CLANG)) { + res = strrchr(s, '$'); + if (res) + *res = '\0'; + } + return res != NULL; } -#else -static inline bool cleanup_symbol_name(char *s) { return false; } -#endif /* Lookup the address for this symbol. Returns 0 if not found. */ unsigned long kallsyms_lookup_name(const char *name) @@ -195,7 +205,7 @@ unsigned long kallsyms_lookup_name(const char *name) if (strcmp(namebuf, name) == 0) return kallsyms_sym_address(i); - if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0) + if (cleanup_symbol_name_thinlto(namebuf) && strcmp(namebuf, name) == 0) return kallsyms_sym_address(i); } return module_kallsyms_lookup_name(name);