linux-kernel - Re: [Query] Stack Overflow in "arch/arm/kernel/unwind.c" while unwinding frame

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Message-ID: <CAPoNrttwS9TdEij_6iDzyHheq+o=nGMV48RaqzayeKCCcqcdjA@mail.gmail.com>
Date:	Sun, 6 Oct 2013 12:44:32 +0530
From:	Anurag Aggarwal <anurag19aggarwal@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Jean Pihet <jean.pihet@...aro.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Query] Stack Overflow in "arch/arm/kernel/unwind.c" while
 unwinding frame

>From what I saw, it happened when the next page is not mapped to
physical memory.

I don't think that stack corruption can cause this.

>From what I could understand about of the code there is not check if
the memory beyond stack is physically mapped or not.

To handle the problem I thought that checks can also be added in
unwind_exec_insn() function for stack overflow.

On Wed, Oct 2, 2013 at 11:41 PM, Catalin Marinas
<catalin.marinas@....com> wrote:
> On 24 September 2013 07:23, Anurag Aggarwal <anurag19aggarwal@...il.com> wrote:
>> While executing unwind backtrace instructions in ARM, in the function
>> unwind_exec_insn()
>> there are chances that SP overflows from stack.
>>
>>
>> For example while executing instruction with opcode 0xAE, vsp can go
>> beyond stack to area that has not been allocated till now.
>>
>> unsigned long *vsp = (unsigned long *)ctrl->vrs[SP];
>> int reg;
>>
>> /* pop R4-R[4+bbb] */
>> for (reg = 4; reg <= 4 + (insn & 7); reg++)
>> ctrl->vrs[reg] = *vsp++;
>>
>> The above scenario can happen while executing any of the unwind instruction.
>>
>> One of the ways to fix the problem is to check for vsp with stack
>> limits before we increment it, but doing it for all the instructions
>> seems a little bad.
>>
>> I just want to know that if anyone has faced the problem before
>
> I haven't seen it but I think with some stack (or unwind bytecode)
> corruption it could happen.
>
> I think we could place some checks only when vsp is assigned and return
> -URC_FAILURE, together with some warning.
>
> --
> Catalin



-- 
Anurag Aggarwal
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