Re: [PATCH v5 2/2] staging: ion: create one device entry per heap

[Benjamin Gaignard]

2017-10-17 0:09 GMT+02:00 Laura Abbott <labbott@xxxxxxxxxx>:
> On 10/10/2017 02:11 AM, Mark Brown wrote:
>> On Mon, Oct 09, 2017 at 05:10:37PM -0700, Laura Abbott wrote:
>>> On 10/09/2017 03:08 PM, Mark Brown wrote:
>>>> On Mon, Oct 09, 2017 at 02:25:47PM -0700, Laura Abbott wrote:
>>
>>>>> Anyway, to move this forward I think we need to see a proof of concept
>>>>> of using selinux to protect access to specific heaps.
>>
>>>> Aren't Unix permissions enough with separate files or am I
>>>> misunderstanding what you're looking to see a proof of concept for?
>>
>>> The goal is to be able to restrict heap access to certain services
>>> and selinux groups on Android so straight unix permissions aren't
>>> sufficient.
>>
>> Oh, there's Android users for this?  The users I was aware of were
>> non-Android.  Though even so I'd have thought that given that SELinux is
>> a superset of Unix file permissions it ought to be sufficient to be able
>> to use them.  I'd been thinking people were suggesting SELinux as a
>> replacement for file permissions, using the single file and the greater
>> capabilities of SELinux.
>>
> Unix file permissions are necessary but not sufficient, they
> can be used separately. Mostly what I want to see before
> merging this is an example that splitting the Ion heaps provides
> more protection than just keeping /dev/ion.
>

To give you an example on my system I have cma regions and so
2 heaps. One is for video decoding/encoding usage and one is dedicated
to display. The goal is to be sure to have enough memory for each devices

With only one /dev/ion nothing (except heap id mask) prohibed one video
apllication to use the cma region dedicated to display.
With one device per heaps I could change the permissions to be sure that
only display have access to the correct heap.
In android init.rc file I will have to change
  chmod 0666 /dev/ion
  chown system graphics /dev/ion

to something like
  chmod 0666 /dev/ion1
  chown system graphics /dev/ion1
  chmod 0666 /dev/ion2
  chown system media /dev/ion2

Android SEpolicy is defined like that
   allow { appdomain -isolated_app } ion_device:chr_file rw_file_perms;
which means that apps could have access to /dev/ion
with multiple devices we can imagine to protect some heap of being used by
the apps, for example like this
   allow { appdomain -isolated_app } ion_device0:chr_file {open ioctl};
   allow { system } ion_device1:chr_file {open ioctl};
  allow { media } ion_device2:chr_file {open ioctl};

Benjamin

> Thanks,
> Laura