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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 8FC8DC43331 for ; Wed, 1 Apr 2020 14:22:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5953120705 for ; Wed, 1 Apr 2020 14:22:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="K3Rq6mtq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733010AbgDAOWk (ORCPT ); Wed, 1 Apr 2020 10:22:40 -0400 Received: from merlin.infradead.org ([205.233.59.134]:33330 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732205AbgDAOWj (ORCPT ); Wed, 1 Apr 2020 10:22:39 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Jt6kQ/7jZjF4jIZ7hA0fedkh4c/2dLW/5f5OfnJUwJc=; b=K3Rq6mtqzo1MfYlTy0XL3DhPfY WphMt+rBISm0SvqpYzIiev/E74tOx3kpd+Q7cYiI9PP7mH3d294QmI4T/HngO8HdeFa3h+LV3LtZK VETPHEJWaYE/BoZgxp5GglRfgdFvfOqg6iNv2384cC8XsoR4MaV8iAfGiuOjDpdKlF4UBVZhYXtau S5njnbWmPbAvwZ/e2VpP8VIXErlQSH+2WCcpks8TcojMDPCGbkiO/OfVeEi2g3b/GFg/cmgfs8oC4 QzgxOGx+Hhbb2AyLNZvIm9IAvlAWqLnXrGP0JousyKNZBf1UoKybMCt8g5Mwf9MGq/rufXcj73hb9 G0cErhlA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jJeGC-0006zU-10; Wed, 01 Apr 2020 14:22:28 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8E00C3060FD; Wed, 1 Apr 2020 16:22:26 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 765F429D8618F; Wed, 1 Apr 2020 16:22:26 +0200 (CEST) Date: Wed, 1 Apr 2020 16:22:26 +0200 From: Peter Zijlstra To: Josh Poimboeuf Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, x86@kernel.org, mhiramat@kernel.org, mbenes@suse.cz, Steven Rostedt Subject: Re: [PATCH v2] objtool,ftrace: Implement UNWIND_HINT_RET_OFFSET Message-ID: <20200401142226.GU20696@hirez.programming.kicks-ass.net> References: <20200330170200.GU20713@hirez.programming.kicks-ass.net> <20200330190205.k5ssixd5hpshpjjq@treble> <20200330200254.GV20713@hirez.programming.kicks-ass.net> <20200331111652.GH20760@hirez.programming.kicks-ass.net> <20200331202315.zialorhlxmml6ec7@treble> <20200331204047.GF2452@worktop.programming.kicks-ass.net> <20200331211755.pb7f3wa6oxzjnswc@treble> <20200331212040.7lrzmj7tbbx2jgrj@treble> <20200331222703.GH2452@worktop.programming.kicks-ass.net> <20200401141402.m4klvezp5futb7ff@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200401141402.m4klvezp5futb7ff@treble> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 01, 2020 at 09:14:02AM -0500, Josh Poimboeuf wrote: > On Wed, Apr 01, 2020 at 12:27:03AM +0200, Peter Zijlstra wrote: > > On Tue, Mar 31, 2020 at 04:20:40PM -0500, Josh Poimboeuf wrote: > > > On Tue, Mar 31, 2020 at 04:17:58PM -0500, Josh Poimboeuf wrote: > > > > > I'm not against adding a second/separate hint for this. In fact, I > > > > > almost considered teaching objtool how to interpret the whole IRET frame > > > > > so that we can do it without hints. It's just that that's too much code > > > > > for this one case. > > > > > > > > > > HINT_IRET_SELF ? > > > > > > > > Despite my earlier complaint about stack size knowledge, we could just > > > > forget the hint and make "iretq in C code" equivalent to "reduce stack > > > > size by arch_exception_stack_size()" and keep going. There's > > > > file->c_file which tells you it's a C file. > > > > > > Or maybe "iretq in an STT_FUNC" is better since this pattern could > > > presumably happen in a callable asm function. > > > > Like so then? > > I'd suggest a patch split like: > > 1) objtool: automagic IRET-in-func > 2) objtool: add RET_OFFSET > 3) ftrace: re-organize asm (and use RET_OFFSET hint) > 4) objtool: remove now-unused SAVE/RESTORE Sure. > > --- a/arch/x86/include/asm/orc_types.h > > +++ b/arch/x86/include/asm/orc_types.h > > @@ -58,8 +58,13 @@ > > #define ORC_TYPE_CALL 0 > > #define ORC_TYPE_REGS 1 > > #define ORC_TYPE_REGS_IRET 2 > > -#define UNWIND_HINT_TYPE_SAVE 3 > > -#define UNWIND_HINT_TYPE_RESTORE 4 > > + > > +/* > > + * RET_OFFSET: Used on instructions that terminate a function; mostly RETURN > > + * and sibling calls. On these, sp_offset denotes the expected offset from > > + * initial_func_cfi. > > + */ > > +#define UNWIND_HINT_TYPE_RET_OFFSET 3 > > I think this comment belongs at the UNWIND_HINT_RET_OFFSET macro > definition. Humph, ok, but there's two of those :/ > > --- a/arch/x86/kernel/ftrace.c > > +++ b/arch/x86/kernel/ftrace.c > > @@ -282,7 +282,8 @@ static inline void tramp_free(void *tram > > > > /* Defined as markers to the end of the ftrace default trampolines */ > > extern void ftrace_regs_caller_end(void); > > -extern void ftrace_epilogue(void); > > +extern void ftrace_regs_caller_ret(void); > > +extern void ftrace_caller_end(void); > > extern void ftrace_caller_op_ptr(void); > > extern void ftrace_regs_caller_op_ptr(void); > > > > @@ -334,7 +335,7 @@ create_trampoline(struct ftrace_ops *ops > > call_offset = (unsigned long)ftrace_regs_call; > > } else { > > start_offset = (unsigned long)ftrace_caller; > > - end_offset = (unsigned long)ftrace_epilogue; > > + end_offset = (unsigned long)ftrace_caller_end; > > op_offset = (unsigned long)ftrace_caller_op_ptr; > > call_offset = (unsigned long)ftrace_call; > > } > > @@ -366,6 +367,13 @@ create_trampoline(struct ftrace_ops *ops > > if (WARN_ON(ret < 0)) > > goto fail; > > > > + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) { > > + ip = ftrace_regs_caller_ret; > > + ret = probe_kernel_read(ip, (void *)retq, RET_SIZE); > > + if (WARN_ON(ret < 0)) > > + goto fail; > > + } > > + > > Hm? This function creates a trampoline but it looks like this change is > overwriting the original ftrace_64 code itself? Ahh. So if you look at what the trampoline copies, you'll note we'll copy until -- but *NOT* including -- the jmp ftrace_epilogue. Instead we'll write a RET at the end. However, due to splitting the return path, such that each instruction has a unique stack offset, we now have a second jmp ftrace_epilogue in the middle of the function. That too needs to be overwritten by a RET. > > --- a/tools/objtool/Makefile > > +++ b/tools/objtool/Makefile > > @@ -31,7 +31,7 @@ INCLUDES := -I$(srctree)/tools/include \ > > -I$(srctree)/tools/arch/$(HOSTARCH)/include/uapi \ > > -I$(srctree)/tools/arch/$(SRCARCH)/include > > WARNINGS := $(EXTRA_WARNINGS) -Wno-switch-default -Wno-switch-enum -Wno-packed > > -CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -g $(INCLUDES) $(LIBELF_FLAGS) > > +CFLAGS := -Werror $(WARNINGS) $(KBUILD_HOSTCFLAGS) -ggdb3 $(INCLUDES) $(LIBELF_FLAGS) > > LDFLAGS += $(LIBELF_LIBS) $(LIBSUBCMD) $(KBUILD_HOSTLDFLAGS) > > Why? Smells like a separate patch at least. Oh, whoops :-) I keep doing this every time I need to run gdb on it. I'll make it go away.