kexec failures with DEBUG_RODATA

[bhe@redhat.com (Baoquan He)]

On 06/14/16 at 11:05am, Kees Cook wrote:
> On Tue, Jun 14, 2016 at 10:59 AM, Russell King - ARM Linux
> <linux@armlinux.org.uk> wrote:
> > Since the kernel now has CONFIG_DEBUG_RODATA by default, this means
> > that these kinds of ratio-based assumptions are even more invalid
> > than they have been.
> >
> > Right now, a zImage doesn't advertise the size of its uncompressed
> > image, but I think with things like CONFIG_DEBUG_RODATA, we can no
> > longer make assumptions like we have done in the past, and we need
> > the zImage to provide this information so that the boot environment
> > can be setup sanely by boot loaders/kexec rather than relying on
> > broken heuristics like this.
> >
> > Thoughts?
> 
> I'm much less familiar with the ARM decompression stub, but is there a
> boot image header (like x86 has)? If not, perhaps we can invent one,
> and it can carry all the details needed for a bootloader to do the
> right things.

Yes, x86 stores addr and size of initrd into boot header. When
decompressing kernel it will choose a safe starting position before the
loaded place according to the max evaluation of decompressing algorithm.

ARM only use a rough 4 times evaluation, sounds too hasty. Simplest way
is to increase times to 8 for now. The final way should be as Kees
suggested.

Thanks
Baoquan