[Ksummit-2013-discuss] [ARM ATTEND] Trustzone-based security solution for ARM Linux

Barry Song 21cnbao at gmail.com
Mon Aug 19 19:31:47 EDT 2013

2013/8/16 Jassi Brar <jassisinghbrar at gmail.com>:
> On Fri, Aug 16, 2013 at 8:09 AM, Barry Song <21cnbao at gmail.com> wrote:
>>>> >>
>>>> >> Isn't that up to the hardware?  Nothing that Linux can do about that.
>>>> >
>>>> > right. but linux need to assign interrupts to right group in GIC
>>>> > hardware. now it doesn't care.
>>>> I strongly hope that whatever is the secure OS is setting up these
>>>> routings, and the HW prevents the non-secure OS from modifying them and
>>>> hence never attempts to. Otherwise, the non-secure OS is able to affect
>>>> the functioning of the secure OS, which seems like a bad thing.
>>> Typically, the master controls are hard-wired for Secure-only access in
>>> hardware: so assigning GIC interrupts to groups is something the secure
>>> OS/firmware has to take care of.
>>> Of course, if Linux is acting as secure OS, it might have to understand
>>> what controls exist and to do some of that configuration itself.
>> that is just what i want. linux need to realize whether it is running
>> in security or non-security.
> TZ should be seen as two platforms tied together. "DTB" for each mode
> should reflect what's available in that mode (dtb for NS kernel
> shouldn't/can't specify any Secure asset and while that of Secure
> kernel should specify anything that is not accessible from NS mode).
> So ideally there should just be the control passing mechanism (like
> SMC command) to be told to the kernel running in NS mode.

we have implemented a prototype which run linux+linux together based
on TZ on mach-prima2.
in the prototype, we did give two different dtb to security-mode linux
and non-security-mode linux.

>> for example, if one irq is assigned to security, even though users
>> want to get it in non-security, linux should make it fail.
>> linux need security/non-security realization in GIC.
> If there is an 'alias' for the secure asset in NS mode, it is better
> to leave it for NS kernel to manage it.
> If some asset is visible in Secure mode only, the NS kernel shouldn't
> be able to simply do an SMC call to have it manipulated. Otherwise we
> leave room for some rooted NS kernel to hack the TrustedOS.
> Point of the rant being, perhaps we don't need new kernel
> policies/designs to enforce TZ security. We just need properly
> partitioned h/w and s/w flow control routed from NS via SMC directly
> to SecureApps(not the Secure Kernel).

we don't need to implement a new kernel. we need to refine a few
drivers to have both security and non-security mode(like GIC and L2
cache), and implement high-level IPC for communication in the two
modes and stolen-time realization for scheduler.

all of above don't mean a new kernel, but mean some refine/cleanup,
TZ- based callbacks and middle-level source codes which can be shared
by all ARM SoC.


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