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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49BEDCD13D8 for ; Sun, 17 Sep 2023 19:26:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239548AbjIQT0Y (ORCPT ); Sun, 17 Sep 2023 15:26:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239698AbjIQT0M (ORCPT ); Sun, 17 Sep 2023 15:26:12 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F9E3119; Sun, 17 Sep 2023 12:26:05 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B67ADC433C9; Sun, 17 Sep 2023 19:26:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1694978765; bh=bZIPkQ41DTNfms13oHVUudCcifvu53l1vSPYEk6CNI8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dw/Qwm4nEGzgoowEvZPGuy9vyHCeJLvQ7jF4t+RHH6VwhUcaqUj8SoZJ5yGYHVH3v Q3RQ5T+kHkyBA7vHBciqBmUXeNnZDdsgyxsFtUEbFqfXZRKoizTSItoyeCqoA52XE9 lL5PwulK261xed0NKEX78vAedm4WVdHOTgOVaVo4= Date: Sun, 17 Sep 2023 12:26:03 -0700 From: Andrew Morton To: Greg Ungerer Cc: linux-arm@lists.infradead.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, eescook@chromium.org, ebiederm@xmission.com, brauner@kernel.org, viro@zeniv.linux.org.uk Subject: Re: [PATCH v2] fs: binfmt_elf_efpic: fix personality for ELF-FDPIC Message-Id: <20230917122603.5466b1fc6d05ea9e9edee340@linux-foundation.org> In-Reply-To: <20230907011808.2985083-1-gerg@kernel.org> References: <20230907011808.2985083-1-gerg@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 7 Sep 2023 11:18:08 +1000 Greg Ungerer wrote: > The elf-fdpic loader hard sets the process personality to either > PER_LINUX_FDPIC for true elf-fdpic binaries or to PER_LINUX for > normal ELF binaries (in this case they would be constant displacement > compiled with -pie for example). The problem with that is that it > will lose any other bits that may be in the ELF header personality > (such as the "bug emulation" bits). > > On the ARM architecture the ADDR_LIMIT_32BIT flag is used to signify > a normal 32bit binary - as opposed to a legacy 26bit address binary. > This matters since start_thread() will set the ARM CPSR register as > required based on this flag. If the elf-fdpic loader loses this bit > the process will be mis-configured and crash out pretty quickly. > > Modify elf-fdpic loader personality setting so that it preserves the > upper three bytes by using the SET_PERSONALITY macro to set it. This > macro in the generic case sets PER_LINUX and preserves the upper bytes. > Architectures can override this for their specific use case, and ARM > does exactly this. > > The problem shows up quite easily running under qemu using the ARM > architecture, but not necessarily on all types of real ARM hardware. > If the underlying ARM processor does not support the legacy 26-bit > addressing mode then everything will work as expected. I'm thinking Fixes: 1bde925d23547 ("fs/binfmt_elf_fdpic.c: provide NOMMU loader for regular ELF binaries") Cc: ?