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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 51942C43219 for ; Wed, 1 May 2019 08:26:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 22D2920835 for ; Wed, 1 May 2019 08:26:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726349AbfEAI0h convert rfc822-to-8bit (ORCPT ); Wed, 1 May 2019 04:26:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:36760 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726014AbfEAI0h (ORCPT ); Wed, 1 May 2019 04:26:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C859AACFA; Wed, 1 May 2019 08:26:34 +0000 (UTC) From: Nicolai Stange To: Steven Rostedt Cc: Linus Torvalds , Andy Lutomirski , Peter Zijlstra , Nicolai Stange , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , "the arch\/x86 maintainers" , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , Shuah Khan , Konrad Rzeszutek Wilk , Tim Chen , Sebastian Andrzej Siewior , Mimi Zohar , Juergen Gross , Nick Desaulniers , Nayna Jain , Masahiro Yamada , Joerg Roedel , Linux List Kernel Mailing , live-patching@vger.kernel.org, "open list\:KERNEL SELFTEST FRAMEWORK" Subject: Re: [RFC][PATCH v2] ftrace/x86: Emulate call function while updating in breakpoint handler References: <20190428133826.3e142cfd@oasis.local.home> <20190430135602.GD2589@hirez.programming.kicks-ass.net> <20190430130359.330e895b@gandalf.local.home> <20190430132024.0f03f5b8@gandalf.local.home> <20190430134913.4e29ce72@gandalf.local.home> <20190430175334.423821c0@gandalf.local.home> Date: Wed, 01 May 2019 10:26:32 +0200 In-Reply-To: <20190430175334.423821c0@gandalf.local.home> (Steven Rostedt's message of "Tue, 30 Apr 2019 17:53:34 -0400") Message-ID: <87muk6vavb.fsf@suse.de> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steve, many thanks for moving this forward! Steven Rostedt writes: > > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index ef49517f6bb2..9160f5cc3b6d 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -17,6 +17,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -232,6 +233,9 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, > > static unsigned long ftrace_update_func; > > +/* Used within inline asm below */ > +unsigned long ftrace_update_func_call; > + > static int update_ftrace_func(unsigned long ip, void *new) > { > unsigned char old[MCOUNT_INSN_SIZE]; > @@ -259,6 +263,8 @@ int ftrace_update_ftrace_func(ftrace_func_t func) > unsigned char *new; > int ret; > > + ftrace_update_func_call = (unsigned long)func; > + > new = ftrace_call_replace(ip, (unsigned long)func); > ret = update_ftrace_func(ip, new); > > @@ -280,6 +286,125 @@ static nokprobe_inline int is_ftrace_caller(unsigned long ip) > return 0; > } > > +/* > + * We need to handle the "call func1" -> "call func2" case. > + * Just skipping the call is not sufficient as it will be like > + * changing to "nop" first and then updating the call. But some > + * users of ftrace require calls never to be missed. > + * > + * To emulate the call while converting the call site with a breakpoint, > + * some trampolines are used along with per CPU buffers. > + * There are three trampolines for the call sites and three trampolines > + * for the updating of the call in ftrace trampoline. The three > + * trampolines are: > + * > + * 1) Interrupts are enabled when the breakpoint is hit > + * 2) Interrupts are disabled when the breakpoint is hit > + * 3) The breakpoint was hit in an NMI > + * > + * As per CPU data is used, interrupts must be disabled to prevent them > + * from corrupting the data. A separate NMI trampoline is used for the > + * NMI case. If interrupts are already disabled, then the return path > + * of where the breakpoint was hit (saved in the per CPU data) is pushed > + * on the stack and then a jump to either the ftrace_caller (which will > + * loop through all registered ftrace_ops handlers depending on the ip > + * address), or if its a ftrace trampoline call update, it will call > + * ftrace_update_func_call which will hold the call that should be > + * called. > + */ > +extern asmlinkage void ftrace_emulate_call_irqon(void); > +extern asmlinkage void ftrace_emulate_call_irqoff(void); > +extern asmlinkage void ftrace_emulate_call_nmi(void); > +extern asmlinkage void ftrace_emulate_call_update_irqoff(void); > +extern asmlinkage void ftrace_emulate_call_update_irqon(void); > +extern asmlinkage void ftrace_emulate_call_update_nmi(void); > + > +static DEFINE_PER_CPU(void *, ftrace_bp_call_return); > +static DEFINE_PER_CPU(void *, ftrace_bp_call_nmi_return); Andy mentioned #DB and #MC exceptions here: https://lkml.kernel.org/r/C55DED25-C60D-4731-9A6B-92BDA8771766@amacapital.net I think that #DB won't be possible, provided the trampolines below get tagged as NOKPROBE (do_int3() and ftrace_int3_handler() already have it). It's highly theoretic, but tracing do_machine_check() could clobber ftrace_bp_call_return or ftrace_bp_call_nmi_return? > +#ifdef CONFIG_SMP > +#ifdef CONFIG_X86_64 > +# define BP_CALL_RETURN "%gs:ftrace_bp_call_return" > +# define BP_CALL_NMI_RETURN "%gs:ftrace_bp_call_nmi_return" > +#else > +# define BP_CALL_RETURN "%fs:ftrace_bp_call_return" > +# define BP_CALL_NMI_RETURN "%fs:ftrace_bp_call_nmi_return" > +#endif > +#else /* SMP */ > +# define BP_CALL_RETURN "ftrace_bp_call_return" > +# define BP_CALL_NMI_RETURN "ftrace_bp_call_nmi_return" > +#endif > + > +/* To hold the ftrace_caller address to push on the stack */ > +void *ftrace_caller_func = (void *)ftrace_caller; The live patching ftrace_ops need ftrace_regs_caller. > + > +asm( > + ".text\n" > + > + /* Trampoline for function update with interrupts enabled */ > + ".global ftrace_emulate_call_irqoff\n" > + ".type ftrace_emulate_call_irqoff, @function\n" > + "ftrace_emulate_call_irqoff:\n\t" > + "push "BP_CALL_RETURN"\n\t" > + "push ftrace_caller_func\n" > + "sti\n\t" > + "ret\n\t" > + ".size ftrace_emulate_call_irqoff, .-ftrace_emulate_call_irqoff\n" > + > + /* Trampoline for function update with interrupts disabled*/ > + ".global ftrace_emulate_call_irqon\n" The naming is perhaps a bit confusing, i.e. "update with interrupts disabled" vs. "irqon"... How about swapping irqoff<->irqon? Thanks, Nicolai > + ".type ftrace_emulate_call_irqon, @function\n" > + "ftrace_emulate_call_irqon:\n\t" > + "push "BP_CALL_RETURN"\n\t" > + "push ftrace_caller_func\n" > + "ret\n\t" > + ".size ftrace_emulate_call_irqon, .-ftrace_emulate_call_irqon\n" > + > + /* Trampoline for function update in an NMI */ > + ".global ftrace_emulate_call_nmi\n" > + ".type ftrace_emulate_call_nmi, @function\n" > + "ftrace_emulate_call_nmi:\n\t" > + "push "BP_CALL_NMI_RETURN"\n\t" > + "push ftrace_caller_func\n" > + "ret\n\t" > + ".size ftrace_emulate_call_nmi, .-ftrace_emulate_call_nmi\n" > + -- SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)