linux-kernel - Re: [PATCH] Fix infinite loop in ARM user perf

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Date:	Mon, 18 Apr 2011 14:02:52 -0700
From:	Sonny Rao <sonnyrao@...omium.org>
To:	Will Deacon <will.deacon@....com>
Cc:	Jamie Iles <jamie@...ieiles.com>, olofj@...omium.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix infinite loop in ARM user perf_event backtrace code

On Mon, Apr 18, 2011 at 10:42 AM, Will Deacon <will.deacon@....com> wrote:
> Hi Sonny,
>
> On Sat, 2011-04-16 at 04:27 +0100, Sonny Rao wrote:
>> The ARM user backtrace code can get into an infinite loop if it
>> runs into an invalid stack frame which points back to itself.
>> This situation has been observed in practice.  Fix it by capping
>> the number of entries in the backtrace.  This is also what other
>> architectures do in their backtrace code.
>>
>> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
>> ---
>>  arch/arm/kernel/perf_event.c |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
>> index 69cfee0..1e61d60 100644
>> --- a/arch/arm/kernel/perf_event.c
>> +++ b/arch/arm/kernel/perf_event.c
>> @@ -746,7 +746,8 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
>>
>>         tail = (struct frame_tail __user *)regs->ARM_fp - 1;
>>
>> -       while (tail && !((unsigned long)tail & 0x3))
>> +       while ((entry->nr < PERF_MAX_STACK_DEPTH) &&
>> +              tail && !((unsigned long)tail & 0x3))
>>                 tail = user_backtrace(tail, entry);
>>  }
>
> Ok. Please can you put this into Russell's patch system?
>
> Will
>

Ok, sent it to patches@....linux.org.uk
hope that'll be sufficient
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