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

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Date:	Tue, 7 Jan 2014 13:53:14 +0000
From:	Dave Martin <Dave.Martin@....com>
To:	Anurag Aggarwal <anurag19aggarwal@...il.com>
Cc:	Anurag Aggarwal <a.anurag@...sung.com>,
	Naveen Kumar <naveen.sel@...sung.com>,
	Narendra Meher <narendra.m1@...sung.com>,
	"nico@...aro.org" <nico@...aro.org>,
	Ashish Kalra <ashish.kalra@...sung.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpgs ." <cpgs@...sung.com>,
	"naveenkrishna.ch@...il.com" <naveenkrishna.ch@...il.com>,
	Rajat Suri <rajat.suri@...sung.com>,
	Poorva Srivastava <poorva.s@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mohammad Irfan Ansari <mohammad.a2@...sung.com>
Subject: Re: [PATCH V6] ARM : unwinder : Prevent data abort due to stack
 overflow

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
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