[PATCH v2 5/5] powerpc/configs: Disable SCOM_DEBUGFS in powernv_defconfig

[Michael Ellerman]

Andrew Donnellan <ajd at linux.ibm.com> writes:
> On 9/5/19 3:54 pm, Andrew Donnellan wrote:
>> On 9/5/19 3:37 pm, Nicholas Piggin wrote:
>>> Andrew Donnellan's on May 9, 2019 3:11 pm:
>>>> SCOM_DEBUGFS is really not needed for anything other than low-level
>>>> hardware debugging.
>>>>
>>>> opal-prd uses its own interface (/dev/prd) for SCOM access, so it 
>>>> doesn't
>>>> need SCOM_DEBUGFS.
>>>>
>>>> At some point in the future we'll introduce a debug config fragment 
>>>> where
>>>> this can go instead.
>>>
>>> That doesn't really explain why you want to disable it. It is useful
>>> for low level hardware debugging, I added it.
>>>
>>> obscurity^Wsecurity?
>> 
>> Mostly just a general feeling that it's not something we need to have by 
>> default. Security-wise, PRD still provides SCOM access, though we are 
>> going to look at how we can further lock that down. Shrinks the build by 
>> only a few kilobytes...
>> 
>> mpe said he's planning on adding a debug.config where we can shift stuff 
>> like this, and if/when we do that I would like to see this moved there, 
>> but perhaps this patch can wait until then. I'll let mpe decide.
>
> mpe do you have thoughts on this? I would like to see at least the rest 
> of this series merged.

I think it should be off by default, it may be true that root can
attack/break the system in many other ways, but providing unrestricted
SCOM access is a pretty big opening.

This is similar to strict /dev/mem IMO, which "everyone" agrees is a
good idea these days.

It's pretty trivial for folks doing development to turn it on in their
local trees, and I would also welcome a debug.config fragment that
enables it.

So I'll take the whole series.

cheers