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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 99EE3C433C1 for ; Sat, 27 Mar 2021 13:03:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6E4A661927 for ; Sat, 27 Mar 2021 13:03:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230233AbhC0NBF (ORCPT ); Sat, 27 Mar 2021 09:01:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:58440 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229582AbhC0NBE (ORCPT ); Sat, 27 Mar 2021 09:01:04 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 75A6561971; Sat, 27 Mar 2021 13:01:03 +0000 (UTC) Date: Sat, 27 Mar 2021 13:01:01 +0000 From: Catalin Marinas To: Andrei Vagin Cc: Will Deacon , Oleg Nesterov , linux-arm-kernel@lists.infradead.org, LKML , Dave Martin , Keno Fischer Subject: Re: [PATCH 1/4] arm64: expose orig_x0 in the user_pt_regs structure Message-ID: <20210327130100.GA31076@arm.com> References: <20210322225053.428615-1-avagin@gmail.com> <20210322225053.428615-2-avagin@gmail.com> <20210326182839.GE5126@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 26, 2021 at 05:35:19PM -0700, Andrei Vagin wrote: > On Fri, Mar 26, 2021 at 11:28 AM Catalin Marinas > wrote: > > > > On Mon, Mar 22, 2021 at 03:50:50PM -0700, Andrei Vagin wrote: > > > diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h > > > index 758ae984ff97..3c118c5b0893 100644 > > > --- a/arch/arm64/include/uapi/asm/ptrace.h > > > +++ b/arch/arm64/include/uapi/asm/ptrace.h > > > @@ -90,6 +90,7 @@ struct user_pt_regs { > > > __u64 sp; > > > __u64 pc; > > > __u64 pstate; > > > + __u64 orig_x0; > > > }; > > > > That's a UAPI change, likely to go wrong. For example, a > > ptrace(PTRACE_GETREGSET, pid, REGSET_GPR, data) would write past the end > > of an old struct user_pt_regs in the debugger. > > ptrace(PTRACE_GETREGSET, ...) receives iovec: > ptrace(PTRACE_GETREGSET, pid, NT_PRSTATUS, &iov) > > iov contains a pointer to a buffer and its size and the kernel fills > only the part that fits the buffer. > I think this interface was invented to allow extending structures > without breaking backward compatibility. You are right here, it doesn't write past the end of the iov buffer. However, it's still an ABI change. An unaware program using a newer user_pt_regs but running on an older kernel may be surprised that the updated iov.len is smaller than sizeof (struct user_pt_regs). Changing this structure also changes the core dump format, see ELF_NGREG and ELF_CORE_COPY_REGS. Maybe this doesn't matter much either since the ELF note would have size information but I'd prefer if we didn't modify this structure. -- Catalin