[U-Boot] [PATCH] ARM: rmobile: Convert to bootm_size

[Simon Goldschmidt]

On Tue, Nov 27, 2018 at 1:25 PM Marek Vasut <marek.vasut at gmail.com> wrote:
>
> On 11/27/2018 08:03 AM, Simon Goldschmidt wrote:
> > On Tue, Nov 27, 2018 at 1:11 AM Marek Vasut <marek.vasut at gmail.com> wrote:
> >>
> >> Convert all Renesas R-Car boards to bootm_size of 256 MiB and drop both
> >> fdt_high and initrd_high. This change implies that the FDT and initrd
> >> will always be copied into the first 256 MiB of RAM instead of being
> >> used in place, which can cause various kinds of inobvious problems.
> >>
> >> The simpler problems include FDT or initrd being overwritten or being
> >> used from unaligned addresses, especially on ARM64. The overhead of
> >> copying the FDT to aligned location is negligible and these problems
> >> go away, so the benefit is significant.
> >>
> >> Regarding alignment problems with fitImage. The alignment of DT properties
> >> is always 32 bits, which implies that the alignment of the "data" property
> >> in fitImage is also 32 bits. The /incbin/ syntax plays no role here. The
> >> kernel expects all elements, including DT and initrd, to be aligned to
> >> 64 bits on ARM64, thus using them in place may not be possible. Using the
> >> bootm_size assures correct alignment, again with negligible overhead.
> >
> > In my opinion, all of these raw addresses defined in scripts or config
> > should be removed: They are probably vulnerable to overwriting
> > themselves as they only provide an address, not a range.
>
> This is not an address, it's size. And this one at least assures that
> the first 256 MiB are reserved for the kernel/FDT/initrd during bootm time.

Sorry I did not express myself clear enough. I meant that "fdt_high"
and "initrd_high" are bad because they contain an address only, not a
range. The 'bootm_size' thing is much better!

> > Just out of curiosity: is it required to put fdt and initrd into the
> > first 256 MiB or is this just some 'random' limit to ensure we use lmb
> > but don't overwrite U-Boot (text, heap, stack, etc)? Because if so, my
> > series to fix the recent CVE issues improves lmb to not overwrite
> > U-Boot and other reserved addresses and you might be able to remove
> > 'bootm_size', too. The improved lmb code would just allocate an
> > aligned address somewhere in the available RAM.
>
> It's just the first 256 MiB from the beginning, so there's enough space
> between that and U-Boot on all these boards.

Of course. I wanted to know if it would be good enough if U-Boot would
just put it somewhere without overwriting things or do you really need
them in the first 256 MiB? Because the revised lmb code would make
sure there's nothing overwritten, so there would be no need to trim at
256 MiB.

Regards,
Simon