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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 290AFC433E0 for ; Thu, 14 May 2020 12:17:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0BABC206A5 for ; Thu, 14 May 2020 12:17:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726389AbgENMRC (ORCPT ); Thu, 14 May 2020 08:17:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1725955AbgENMRB (ORCPT ); Thu, 14 May 2020 08:17:01 -0400 Received: from Galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90A7EC061A0C for ; Thu, 14 May 2020 05:17:01 -0700 (PDT) Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jZCms-0005wZ-KQ; Thu, 14 May 2020 14:16:30 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id C5F561004CE; Thu, 14 May 2020 14:16:29 +0200 (CEST) From: Thomas Gleixner To: Andy Lutomirski Cc: LKML , X86 ML , "Paul E. McKenney" , Andy Lutomirski , Alexandre Chartre , Frederic Weisbecker , Paolo Bonzini , Sean Christopherson , Masami Hiramatsu , Petr Mladek , Steven Rostedt , Joel Fernandes , Boris Ostrovsky , Juergen Gross , Brian Gerst , Mathieu Desnoyers , Josh Poimboeuf , Will Deacon Subject: Re: [patch V4 part 3 13/29] x86/traps: Prepare for using DEFINE_IDTENTRY In-Reply-To: References: <20200505134354.774943181@linutronix.de> <20200505134904.556327833@linutronix.de> Date: Thu, 14 May 2020 14:16:29 +0200 Message-ID: <87mu6azp7m.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andy, Andy Lutomirski writes: > On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner wrote: >> >> +static __always_inline void __user *error_get_trap_addr(struct pt_regs *regs) >> +{ >> + return (void __user *)uprobe_get_trap_addr(regs); >> +} > > My mind boggles. WTF is this? That's an inline version of the same nonsense in that macro maze. > Perhaps this should have a comment like: > > /* > * Returns the address from which a user trap originated. This would be the same as regs->ip, > * except for frhgnieawfn nvlrkvklsrvs and mfkealwf, and this lets the thingummy pass a > * modified value to the signal frame, but only for #DE and #UD, because #*!&@&#@. > */ > > except with the blanks filled in. Hmm. Filling the blanks gives me: /* **0Returns1the2address3from4which5a6user7trap8originated.90This1would... That's not really more readable than yours :) > After reading a bit of uprobe code, I assume this is a fixup for when > we're running code that got moved out of line because it got replaced > by a breakpoint. I'm still mystified by why it only seems to apply to > #DE and #UD. man sigaction(2): * SIGILL, SIGFPE, SIGSEGV, SIGBUS, and SIGTRAP fill in si_addr with the address of the fault. On some architectures, these signals also fill in the si_trapno field. Posix spec says: In addition, the following signal-specific information shall be available: Signal Member Value SIGILL void * si_addr Address of faulting instruction. SIGFPE SIGSEGV void * si_addr Address of faulting memory reference. SIGBUS For some implementations, the value of si_addr may be inaccurate. In historic kernels si_addr was simply set to regs->ip and the uprobe muck changed that in commit b02ef20a9fba08 ("uprobes/x86: Fix the wrong ->si_addr when xol triggers a trap") If the probed insn triggers a trap, ->si_addr = regs->ip is technically correct, but this is not what the signal handler wants; we need to pass the address of the probed insn, not the address of xol slot. Now that I filled my own blanks, I think that I can come up with a halfways useful comment. Thanks, tglx