[U-Boot] u-boot on raspberry 2: booting in SVC secure mode

[Andre Przywara <andre.przywara@arm.com>]

Hi Vincent,

On 26/02/15 08:27, Vincent wrote:
> Hi,
> I finally hacked my way through U-boot and I managed to add raspberry's
> boot code inside U-boot so that it can start as usual when using kernel_old
> = 1. I don't think
> we want this as a final solution but it made me understand a few things
> about U-boot architecture (in short: I added a new section located at 0x0
> which executes raspberry's code, and
> then jump to the usual _start entry point). I didn't try to modify
> CONFIG_SYS_TEXT_BASE yet, I'll try this morning.
> 
> From what I gathered from the source code, I think I have to activate some
> options (like the ones in arch/arm/cpu/armv7/Kconfig) so that U-boot starts
> in secure mode,
> but adding them to rpi_2_defconfig doesn't seem to change anything in
> .config, so I'm not sure that my current U-boot is "secure boot aware".
> Should I add ARMV7_BOOT_SEC_DEFAULT by hand in .config or something like
> that ?

AFAIK you don't need to tell U-Boot that it runs in secure: unless it
accesses any secure/non-secure specific peripherals it should work fine
in both modes.
Setting ARMV7_BOOT_SEC_DEFAULT just prevents U-Boot to switch into
non-sec, but there is no real reason to do so - at least not for Linux.

You should do away with the original Raspi firmware snippet - not only
from a legal point of view.
Thanks to Marc U-Boot has now a much better implementation than my
original HYP-mode switcher, also this gives you PSCI support basically
for free. So just select ARMV7_VIRT and ARMV7_NONSEC.

Do you know if there is a TrustZone Controller in that SoC? That would
be needed to guard the resident U-Boot code from the OS. Some SoCs have
secure on-chip SRAM usable for that purpose, that would do it, too.
But skimming through the BCM2835 .pdf I don't spot any of those,
unfortunately.

Cheers,
Andre.

> 
> 2015-02-25 19:38 GMT+01:00 Stephen Warren <swarren@wwwdotorg.org>:
> 
>> On 02/25/2015 02:30 AM, Vincent wrote:
>>
>>> Hi,
>>> as explained here http://community.arm.com/message/25127, it is possible
>>> to
>>> boot the raspberry 2 in secure mode, by adding the kernel_old=1 option in
>>> config.txt. The main effects of this option are:
>>> - all 4 cores start executing in secure SVC mode instead of non-secure SVC
>>> mode
>>> - all 4 cores start at 0x0000 instead of 0x8000
>>> - the initial boot code that setup SMP and exits secure mode is not
>>> executed
>>>
>>> After browsing u-boot's source code, it seems that their boot code is more
>>> or less extracted from what u-boot is doing. However I didn't manage to
>>> compile u-boot for the raspberry 2 supporting this secure mode.
>>>
>>> Could anyone explain me what options I need to configure in
>>> rpi_2_defconfig
>>> so that u-boot supports secure boot for the raspberry 2 and what the boot
>>> sequence will be in this case ? I don't mind fixing the code if necessary
>>> but I'm a bit lost in the order of events in the initialization.
>>>
>>
>> (Luckily I just happened to notice this message while looking at another
>> one nearby. CCing the relevant board maintainer(s) explicitly would help
>> your messages be noticed)
>>
>> To modify U-Boot to support the alternate entry point/load address, you'd
>> hopefully only need to change the definition of CONFIG_SYS_TEXT_BASE in
>> include/configs/rpi*.h.
>>
>> I wasn't aware of the thread/option you mention, so I have not attempted
>> to boot the RPi2 U-Boot in secure mode. If you're lucky, U-Boot itself will
>> "just work" once TEXT_BASE is fixed.
>>
>> To boot a kernel, you'll probably need to at least configure the ARM
>> architected timers CNTFRQ register for the kernel. Perhaps there are a few
>> other things like that missing?
>>
>> It might be interesting to enable U-Boot's PSCI support on the RPi2, so
>> that an upstream kernel could gain SMP support without the need for
>> explicit BCM2836 SMP support code.
>>
>> So far, I haven't attempted anything with an (upstream) kernel on RPi2,
>> just U-Boot.
>>
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