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SubjectRe: Regression with arm in next with stack protector
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.

--
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