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

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Message-ID: <20131209142212.GA4281@e103592.cambridge.arm.com>
Date:	Mon, 9 Dec 2013 14:22:17 +0000
From:	Dave Martin <Dave.Martin@....com>
To:	Anurag Aggarwal <anurag19aggarwal@...il.com>
Cc:	"naveen.sel@...sung.com" <naveen.sel@...sung.com>,
	"narendra.m1@...sung.com" <narendra.m1@...sung.com>,
	"nico@...aro.org" <nico@...aro.org>,
	Anurag Aggarwal <a.anurag@...sung.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ashish.kalra@...sung.com" <ashish.kalra@...sung.com>,
	"cpgs@...sung.com" <cpgs@...sung.com>,
	"naveenkrishna.ch@...il.com" <naveenkrishna.ch@...il.com>,
	"rajat.suri@...sung.com" <rajat.suri@...sung.com>,
	"poorva.s@...sung.com" <poorva.s@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"mohammad.a2@...sung.com" <mohammad.a2@...sung.com>
Subject: Re: [PATCH] ARM : unwinder : Prevent data abort due to stack overflow

On Sat, Dec 07, 2013 at 01:43:21PM +0530, Anurag Aggarwal wrote:
> >>
> >> +     /* we are just starting, initialize last register set as 0 */
> >> +     ctrl.last_register_set = 0;
> >> +
> >>       while (ctrl.entries > 0) {
> >> -             int urc = unwind_exec_insn(&ctrl);
> >> +             int urc;
> >> +             if ((ctrl.sp_high - ctrl.vrs[SP]) < TOTAL_REGISTERS)
> >> +                     ctrl.last_register_set = 1;
> >
> >If this is done once per unwind_exec_insn(), I think it would be better
> >to put the check at the start of unwind_exec_insn() instead of outside.
> 
> I think it is better to do the above check here only because this check
> is strictly not a part of decoder and execution cycle.
> 
> I think uniwnd_exec_insn(), should only be used for decoding and
> execution of instruction, as you have suggested earlier. So, it makes
> sense to keep it in unwind_frame only().

It's debatable, since the stack checking is an intrinsic part of insn
execution.  But since there is only one call site for unwind_exec_insn
and it is unlikely than another will appear in the future, I am happy
for it to remain in your current form.

Cheers
---Dave
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