Re: [PATCH V6] ARM : unwinder : Prevent data abort due to stack overflow

[Dave Martin <Dave.Martin@arm.com>]

On Sat, Dec 14, 2013 at 03:47:49PM +0530, Anurag Aggarwal wrote:
> >You could try adding some debug printks to see how the backtrace fails.
> >You could also try adding a few hand-crafted assembler functions
> >with appropriate code and unwind directives to trigger different kinds
> >of backtrace failure.  You might have to add a way to artificially limit
> >sp_high to check the cases where you run out of stack in the middle of
> >popping multiple registers.
> 
> I added a a printk statement
> +               if (*vsp >= (unsigned long *)ctrl->sp_high) {
> +                       printk(KERN_ERR "Stack Overflow Detected, vsp = %lx",
> +                               (unsigned long)*vsp);
> +                       return -URC_FAILURE;
> +               }
> 
> I ran a many test cases to try and get the above print in the dmesg log.
> 
> I tried the following things :
> 
> 1) Calling unwind_backtrace from diffrenet locations in the kernel, I
> added the unwind call
> in some irq, fork, exit and some sysfs entries call.
> 2) I limited the value of sp_high in unwind_frame() itself, I tried
> many values of sp_high,
> varrying from (low + sizeof(ctrl.vrs)/4) to (low + 4*sizeof(ctrl.vrs)).
> 
> When running the above cases I was able to see the above printk quiet
> a few times in dmesg log.
> 
> So, the error condition is being handled.
> 
> If you have some test cases for verifying the unwinder, please share
> the same. They might help
> in thorough testing of unwinder.

I think that sounds OK to give us reasonable confidence that the code is
working correctly.

Go ahead and add my Reviewed-by on the patch, if you're still waiting
for it.

Cheers
---Dave