Configuration option for thread-stack protection.

[Gedare Bloom]

On Thu, Aug 6, 2020 at 6:21 AM Sebastian Huber
<sebastian.huber at embedded-brains.de> wrote:
>
> On 06/08/2020 14:12, Utkarsh Rai wrote:
>
> > Hello,
> > The thread-stack protection needs to be configured by the user. Two of
> > the options that need configuring during build time are -
> > > Enabling thread stack protection ( THREAD_STACK_PROTECTION )- This
> > is a high-level option similar to RTEMS_SMP, RTEMS_POSIX_API  etc.
> > > Size of the MMU pages - This is a BSP specific option.
> >  Using the new build system we can configure these by adding BSP
> > option ( for eg. realview BSP has 'optmmusmallpages.yml'  for 4K mmu
> > pages). Similarly, we can have 'optthreadstackprotection.yml' similar
> > to 'optsmp.yml' for enabling thread stack protection.  Is there
> > something else we need to do, for specifying these options?
> >
> > Another option that needs to be specified is the number of thread
> > stacks that can be shared with a particular thread. This can be done
> > by specifying this in rtems/confdefs.h and then configured by the
> > application. I would request your opinion on this and whether this is
> > the right manner to proceed.
>
> Yes, we probably need a new CPU option RTEMS_THREAD_STACK_PROTECTION or
> similar.
>
+1
Just copy one of the existing high-level switches and give it a try,
see how it turns out.

> Why can't you use this option in the BSP to enable the 4KiB pages MMU?
>
Agreed. This one can be solved with documentation specific to the
BSP/CPU related to how to configure it for stack protection.

> With respect to the application configuration, we should consider to use
> thread-local storage for this. TLS is well supported on ARM, SPARC,
> PowerPC, RISC-V, and m68k.
>
I'm not sure if I follow this thought all the way.

Would the idea be to have the application populate some data structure
with the pointers/names of stacks it needs to access in the TLS? And
then maybe we have something that converts that structure into an
internal representation, something that is kind of like a page table.

Do we have a documented way of using TLS?

Gedare