From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: Regression with arm in next with stack protector Date: Tue, 27 Mar 2018 12:34:53 +0100 Message-ID: <20180327113453.GC10990@n2100.armlinux.org.uk> References: <20180323181452.GJ5799@atomide.com> <20180327090409.GA10990@n2100.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20180327090409.GA10990@n2100.armlinux.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Tony Lindgren Cc: Stephen Rothwell , Rich Felker , Yoshinori Sato , linux-kernel@vger.kernel.org, Ralf Baechle , linux-omap@vger.kernel.org, Huacai Chen , Andrew Morton , James Hogan , linux-arm-kernel@lists.infradead.org List-Id: linux-omap@vger.kernel.org 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. Is there any reason we can't do this in misc.c: const unsigned int __stack_chk_guard = 0x000a0dff; ? That would save having runtime code to set that value up, and after all, it is constant. Arguments about it potentially ending up at a fixed offset into the image need not be said - that's already the case with placing it in the early assembly code, and as has been established, it needs to be initialised prior to any C code being called. -- 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