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=-5.0 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 B4B49C5517A for ; Fri, 30 Oct 2020 16:53:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31E012075E for ; Fri, 30 Oct 2020 16:53:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=armlinux.org.uk header.i=@armlinux.org.uk header.b="jX3FXm1X" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726424AbgJ3Qxp (ORCPT ); Fri, 30 Oct 2020 12:53:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57588 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725844AbgJ3Qxp (ORCPT ); Fri, 30 Oct 2020 12:53:45 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D5EC0C0613CF; Fri, 30 Oct 2020 09:53:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=KEeA33OEqDGWbAtgRNQqJFf7DgtZxfBU7JaReRDm16k=; b=jX3FXm1XC8wFy0ppOFkRv0VZg S/xciqwX5i4N+Lb7KH1fWrhIUHgt+d8DdDmlJ1tX5644PUSgZ+NHLdh6K0IaR4IHPTQ5eyGe/SV44 eEA4Sz7tvDIvBgMj6t2nocefChfW3EP3RX/x2Ch/f05gnqOtRAmPyLFjHBySJx6LZtcsJfixpP/04 vbftM9PvBzSxTYvr2a3H2GzWPOd6JBffM9umOGDmEgptm6jukqAoSIbCllqnhfKs8283efkI6tcMh LMF2s9QxgP7W/VKypWL/4AJ3OoYBqk9ceaTWO4dukcWLCV+D5FJBA9iWz9hW5J7L9chX3TfkUM20O 3/N2Sf7mg==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:52960) by pandora.armlinux.org.uk with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1kYXem-0006Ot-8l; Fri, 30 Oct 2020 16:53:40 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.92) (envelope-from ) id 1kYXel-0007KL-3L; Fri, 30 Oct 2020 16:53:39 +0000 Date: Fri, 30 Oct 2020 16:53:39 +0000 From: Russell King - ARM Linux admin To: Arnd Bergmann Cc: Christoph Hellwig , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, viro@zeniv.linux.org.uk, linus.walleij@linaro.org, arnd@arndb.de Subject: Re: [PATCH 4/9] ARM: syscall: always store thread_info->syscall Message-ID: <20201030165338.GG1551@shell.armlinux.org.uk> References: <20201030154519.1245983-1-arnd@kernel.org> <20201030154919.1246645-1-arnd@kernel.org> <20201030154919.1246645-4-arnd@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201030154919.1246645-4-arnd@kernel.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: Russell King - ARM Linux admin Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 30, 2020 at 04:49:14PM +0100, Arnd Bergmann wrote: > From: Arnd Bergmann > > The system call number is used in a a couple of places, in particular > ptrace, seccomp and /proc//syscall. > > The last one apparently never worked reliably on ARM for tasks > that are not currently getting traced. > > Storing the syscall number in the normal entry path makes it work, > as well as allowing us to see if the current system call is for > OABI compat mode, which is the next thing I want to hook into. I'm not sure this patch is correct. Tracing the existing code for OABI: asmlinkage int syscall_trace_enter(struct pt_regs *regs, int scno) { current_thread_info()->syscall = scno; /* Legacy ABI only. */ USER( ldr scno, [saved_pc, #-4] ) @ get SWI instruction bic scno, scno, #0xff000000 @ mask off SWI op-code eor scno, scno, #__NR_SYSCALL_BASE @ check OS number tst r10, #_TIF_SYSCALL_WORK @ are we tracing syscalls? bne __sys_trace __sys_trace: mov r1, scno add r0, sp, #S_OFF bl syscall_trace_enter So, thread_info->syscall does not include __NR_SYSCALL_BASE. The reason for this is the code that makes use of that via syscall_get_nr(). kernel/trace/trace_syscalls.c: syscall_nr = trace_get_syscall_nr(current, regs); if (syscall_nr < 0 || syscall_nr >= NR_syscalls) return; and NR_syscalls is the number of syscalls, which doesn't include the __NR_SYSCALL_BASE offset. So, I think this patch actually breaks OABI. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!