linux-kernel - Re: [PATCH 3/3] perfcounter: Align ftrace events raw samples to 8 bytes

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Date:	Mon, 10 Aug 2009 09:13:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 3/3] perfcounter: Align ftrace events raw samples to 8
 bytes

On Sat, 2009-08-08 at 04:26 +0200, Frederic Weisbecker wrote:
> Align the ftrace events raw samples to 8 bytes so that they meet the
> perf output event alignements requirements.
> 
> Reported-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Mike Galbraith <efault@....de>
> Cc: Paul Mackerras <paulus@...ba.org>
> ---
>  include/trace/ftrace.h |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index 80e5f6c..7b0834c 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -687,7 +687,7 @@ static void ftrace_profile_##call(proto)				\
>  	pc = preempt_count();						\
>  									\
>  	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
> -	__entry_size = __data_size + sizeof(*entry);			\
> +	__entry_size = ALIGN(__data_size + sizeof(*entry), sizeof(u64));\
>  									\
>  	do {								\
>  		char raw_data[__entry_size];				\

Make sure to clear the trailing few bytes, otherwise we've got a stack
data leak here.

Also, tracepoints using __string() could still easily overflow the stack
here and cause great havoc, esp since the tracepoint could already be
deep into a call-chain.


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