From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754975AbeC0RU6 (ORCPT ); Tue, 27 Mar 2018 13:20:58 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:34388 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754831AbeC0RUy (ORCPT ); Tue, 27 Mar 2018 13:20:54 -0400 Date: Tue, 27 Mar 2018 18:20:27 +0100 From: Russell King - ARM Linux To: Rich Felker Cc: Tony Lindgren , Huacai Chen , Andrew Morton , Stephen Rothwell , Ralf Baechle , James Hogan , Yoshinori Sato , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-omap@vger.kernel.org Subject: Re: Regression with arm in next with stack protector Message-ID: <20180327172027.GA14598@n2100.armlinux.org.uk> References: <20180323181452.GJ5799@atomide.com> <20180327090409.GA10990@n2100.armlinux.org.uk> <20180327153525.GI1436@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180327153525.GI1436@brightrain.aerifal.cx> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Mar 27, 2018 at 11:35:25AM -0400, Rich Felker wrote: > On Tue, Mar 27, 2018 at 10:04:10AM +0100, Russell King - ARM Linux wrote: > > On Fri, Mar 23, 2018 at 11:14:53AM -0700, Tony Lindgren wrote: > > > Hi, > > > > > > Looks like commit 5638790dadae ("zboot: fix stack protector in > > > compressed boot phase") breaks booting on arm. > > > > > > This is all I get from the bootloader on omap3: > > > > > > Starting kernel ... > > > > > > data abort > > > pc : [<810002d0>] lr : [<100110a8>] > > > reloc pc : [<9d6002d0>] lr : [<2c6110a8>] > > > sp : 81467c18 ip : 81466bf0 fp : 81466bf0 > > > r10: 80fc2c40 r9 : 81000258 r8 : 86fec000 > > > r7 : ffffffff r6 : 81466bf8 r5 : 00000000 r4 : 80008000 > > > r3 : 81466c14 r2 : 81466c18 r1 : 000a0dff r0 : 00466bf8 > > > Flags: nZCv IRQs off FIQs off Mode SVC_32 > > > Resetting CPU ... > > > > > > resetting ... > > > > The reason for this is the following code that was introduced by the > > referenced patch: > > > > + ldr r0, =__stack_chk_guard > > + ldr r1, =0x000a0dff > > + str r1, [r0] > > > > This uses the absolute address of __stack_chk_guard in the decompressor, > > which is a self-relocatable image. As with all constructs like the > > above, this absolute address doesn't get fixed up, and so it ends up > > pointing at invalid memory (in this case 0x466bf8) vs RAM at 0x80000000, > > and the decompressor looks to be around 0x81000000. > > > > Such constructs can not be used in the decompressor for exactly this > > reason - they need to use PC-relative addressing instead just like > > everything else does in head.S. > > Can someone please answer why this is even needed to begin with? I > don't see any compelling reason __stack_chk_guard needs a particular > value in the decompressor, which is not dealing with any non-constant > input. Untrue - it can do some parsing of the DT and updating/appending information from ATAGs. However, all that should be coming from a trusted environment, so I don't see much of a "trust" issue here. (If the parent environment is not trusted, then the environment we're running in is not trusted.) > Just putting __stack_chk_guard in its bss should be fine and > would eliminate all the risks of wrong code to load a value into it. > Alternatively put it in initialized data with the desired value. I'm no expert with this, so I can't comment. I build my kernels with gcc 4.7.4, which I don't think supports this feature. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 8.8Mbps down 630kbps up According to speedtest.net: 8.21Mbps down 510kbps up