On 14-01-23 07:58 AM, Detlev Zundel wrote:
Hi Bhupesh,
-----Original Message-----
From: u-boot-boun...@lists.denx.de [mailto:u-boot-boun...@lists.denx.de]
On Behalf Of drambo
Sent: Thursday, January 23, 2014 12:32 AM
To: u-boot@lists.denx.de
Subject: Re: [U-Boot] how to get u-boot code with arm64: core support
Hi Bhupesh,
U-boot doesn't have ARM trusted firmware support as of now. U-boot for
ARMv8 starts in EL3, whereas UEFI starts in EL2 as trusted firmware
itself is working in EL3.
Since the ATF software doesn't really care whether it is loading uefi or
u-boot and since it wants to load non-secure images as EL2 or EL1
(https://github.com/ARM-software/arm-trusted-
firmware/blob/master/docs/user-guide.md
See section "Normal World Software Execution"), why would we want to
assume u-boot starts in EL3 mode by default?
If we want to support EL3 execution for convenience to those that don't
have ATF setup, that might make sense, but then shouldn't initial EL3
execution and subsequent switching levels be debug CONFIG options?
Thanks.
In the past I remember using u-boot as the bare-metal s/w to debug a
Silicon without any BootROM/firmware code running before the same on
ARM 32-bit architectures.
Many of our customers (in the embedded market) use U-Boot in such a way
very successfully.
armv8 and ATF bring in a new security model and with that, secure
monitor/dispatch, secure OS support and secure power control. It may not
be good to assume that we can work in a historical way here.
The ATF is presently tested only for UEFI and UEFI comes up in EL2
while the ATF itself is running in EL3.
I don't know what would be the popular vote on this, but personally I
feel that the u-boot for ARMv8 should also be launched by the ATF
(similar to UEFI) and should start execution in EL2 so that it can
launch a hypervisor (running in EL2) or Linux (running in EL1). But
this might hurt the popular premise that u-boot can be used as a
bare-metal s/w to debug a silicon without additional firmware
components.
Perhaps u-boot experts can guide us on this !
I have to admit that I'm only reading up on the complexities of the
security model of aarch64, but my gut response (cf. [1] is that "real
security" stems from "few code" rather than adding layer over layer.
With this in mind, I'd really like to see that U-Boot with its well
known and tested code base can still be the "root of trust" in an
embedded product (i.e. EL3 as far as I understand).
EL3 is the highest level of trust, and the new armv8 security model
treats uefi/u-boot as non-secure firmware. The ATF trusted firmware
needs to run, initialize secure hardware, load trusted images, and
ultimately launch the non-secure OS loader (uefi or u-boot). As such, I
think that running uefi or u-boot at EL3 violates the current arm
security model i.e. u-boot cannot be the "root of trust" in this
architecture since it is non-secure. Having non-secure firmware run at
the same level as the secure dispatcher and secure monitor will fail any
secure audit in my opinion.
However, if we set up u-boot so that it can wake up at any security
level and migrate to non-secure EL1, that might be a nice compromise.
But having specific EL3 startup assumptions and code that is always
present in u-boot seems like the wrong approach to me. At the very
least, we should wrap the EL3 code in a CONFIG option since this is not
the planned entry state for final deployment.
Note that these are just my opinions above. Any ARM security experts
would be welcome to contribute thoughts here.
Many of the embedded U-Boot users who excercise full control over the
whole software stack very likely want to see the same.
The ATF secure software is freely available.
The interesting question will be if we can reconcile the requirements of
"classic embedded U-Boot users" and this "OEM server market" that seems
to drive much of these new concepts here. But I sincerely hope so.
After all, in the end we want to boot an OS to get the real work done ;)
As armv8 goes mobile, we have less of a server market issue and more of
a mobile security issue.
Best wishes
Detlev
[1] Reading one presentation I found about ATF[2] actually made my head
hurt around page 12 which looks more like "security soup" than
clearcut concepts, but maybe I'm just not into all the details yet.
[2] http://lcu-13.zerista.com/event/member/85121
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