[U-Boot] [PATCH v2 14/15] Introduce arch_phys_memset which works like memset but on physical memory

[Simon Glass]

Hi Tom,

On Mon, Dec 3, 2012 at 5:59 AM, Tom Rini <trini at ti.com> wrote:
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> On 12/02/12 09:55, Simon Glass wrote:
>> From: Gabe Black <gabeblack at chromium.org>
>>
>> The default implementation of this function is just memset, but
>> other implementations will be needed when physical memory isn't
>> accessible by U-Boot using normal addressing mechanisms.
>>
>> Signed-off-by: Gabe Black <gabeblack at chromium.org> Signed-off-by:
>> Che-Liang Chiou <clchiou at chromium.org> Signed-off-by: Simon Glass
>> <sjg at chromium.org>
>
> We've supported PowerPC platforms with 36bit memory ranges for ages.
> Part of that however I believe is just not touching that high memory
> range.  So why do we need to touch the range here, rather than just
> configuring the memory controller and booting Linux?  Is this for some
> hardware tester for example?

We need to clear all memory as part of the secure boot, to avoid
attacks which involve leaving code around over a reboot, etc. For x86
also we avoid touching memory above 4GB during normal operation, but
it isn't enough to just ignore it, since there might be something
lurking there that someone can invoke. The support is minimal (just
clearing it) and we don't want to start using it in any other way.

Regards,
Simon

>
> - --
> Tom
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