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

[Marek Vasut]

On 11/27/2018 04:26 PM, Simon Goldschmidt wrote:
> On 27.11.2018 14:09, Marek Vasut wrote:
>> On 11/27/2018 01:33 PM, Simon Goldschmidt wrote:
>>> 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!
>> Well the fdt_high and intrd_high can also contain a special ~0 value,
>> which says "use the fdt/initrd in place", which is dangerous.
>>
>>>>> 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.
>> You can put them anywhere, you just need to meet the alignment
>> requirements. Can the new LMB code help somehow with that ? And if so,
>> how ?
> 
> My additions to the LMB code should only ensure nothing gets overwritten
> so you don't have to limit boom_size to 256MiB (but use the complete RAM
> when bootm_size is not set).
> Alignment does not change but should already be OK with LMB as you use it?

If I can use the entire RAM (except U-Boot and fitImage), that'd be
nice. What change do I need to do ?

-- 
Best regards,
Marek Vasut