Re: More linux emulation

[Robert Swindells <rjs%fdy2.co.uk@localhost>]

Matt Thomas wrote:
>On Apr 3, 2014, at 12:42 PM, Christos Zoulas <christos%astron.com@localhost> 
>wrote:
>
>> In article <20140403192802.9D98112967%ren.fdy2.co.uk@localhost>,
>> Robert Swindells  <rjs%fdy2.co.uk@localhost> wrote:
>>> 
>>> I have added a change to the arm copy of linux_syscall.c that lets
>>> it start running Debian armel binaries, I would expect armhf ones
>>> to run too.
>>> 
>>> Current ARM Linux expects there to be some helper functions at the top
>>> of the high vectors page that can be called from userspace.
>>> 
>>> These functions do things like compare-and-swap, memory barrier and
>>> give fast access to the TLS pointer. The idea is that they can have
>>> processor specific versions of these with a generic userland.
>>> 
>>> Do people think it would be a bad idea to add this feature ?
>>> 
>>> I haven't worked out what security issues there might be with it.
>>> 
>>> Robert Swindells
>> 
>> I don't see that this is a problem. There is a lot of prior art doing similar
>> things (getpid() fast memcpy(), timer access etc).
>
>well, most platforms don't use high vectors anymore.  And that page is
>usually not user-readable.

I was more worried about exposing whatever else was in our vectors
page to userspace. Just creating a page containing these functions
would be simpler.

One idea was to create an arm specific linux_exec_setup_stack() and
add the mapping of this page to it.