[U-Boot] [PATCH 1/3] ARM: HYP/non-sec: save and restore stack

[Alexander Graf]

On 12.06.18 22:17, Mark Kettenis wrote:
>> From: Alexander Graf <agraf at suse.de>
>> Date: Tue, 12 Jun 2018 20:46:02 +0200
>>
>> On 12.06.18 19:27, Mark Kettenis wrote:
>>> The current code that switches into HYP mode doesn't bother to set
>>> up a stack for HYP mode.  This doesn't work for EFI applications
>>> as they expect a usable stack.  Fix this by saving the stack
>>> pointer before switching and use it to set SP_hyp from monitor.
>>> This restores the stack pointer when we drop into HYP mode.
>>>
>>> Signed-off-by: Mark Kettenis <kettenis at openbsd.org>
>>
>> Can we be sure that the stack in MON is usable from HYP?
> 
> I think so.  It is the stack that U-Boot sets up for itself in normal
> memory.  As far as I can tell arm64 re-uses this stack when dropping
> down into EL2 as well.

Well, the question is whether it's secure or non-secure memory. Usually
the DRAM controller can be configured to have a window of RAM only
available to secure and I'd certainly hope that at least the U-Boot
parts that are preserved in EL3 live in such a secured area :)


Alex