Re: [PATCH] perf: Fix unsafe frame rewinding with hot regs fetching

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 08 avril 2010 à 14:32 +0200, Frederic Weisbecker a écrit :


> 
> Can you please test this fix?
> 
> Thanks.
> 
> ---
> From 60d5c4e8498efc4a01abceef54ad3bc91993bf41 Mon Sep 17 00:00:00 2001
> From: Frederic Weisbecker <fweisbec@gmail.com>
> Date: Thu, 8 Apr 2010 14:05:50 +0200
> Subject: [PATCH] perf: Fix unsafe frame rewinding with hot regs fetching
> 
> When we fetch the hot regs and rewind to the nth caller, it
> might happen that we dereference a frame pointer outside the
> kernel stack boundaries, like in this example:
> 
> 	perf_trace_sched_switch+0xd5/0x120
>         schedule+0x6b5/0x860
>         retint_careful+0xd/0x21
> 
> Since we directly dereference a userspace frame pointer here while
> rewinding behind retint_careful, this may end up in a crash.
> 
> Fix this by simply using probe_kernel_address() when we rewind the
> frame pointer.
> 
> This issue will have a much more proper fix in the next version of the
> perf_arch_fetch_caller_regs() API that will only need to rewind to the
> first caller.
> 
> Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: David Miller <davem@davemloft.net>
> Cc: Archs <linux-arch@vger.kernel.org>
> ---
>  arch/x86/kernel/dumpstack.h |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/dumpstack.h b/arch/x86/kernel/dumpstack.h
> index e39e771..e1a93be 100644
> --- a/arch/x86/kernel/dumpstack.h
> +++ b/arch/x86/kernel/dumpstack.h
> @@ -14,6 +14,8 @@
>  #define get_bp(bp) asm("movq %%rbp, %0" : "=r" (bp) :)
>  #endif
>  
> +#include <linux/uaccess.h>
> +
>  extern void
>  show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
>  		unsigned long *stack, unsigned long bp, char *log_lvl);
> @@ -42,8 +44,10 @@ static inline unsigned long rewind_frame_pointer(int n)
>  	get_bp(frame);
>  
>  #ifdef CONFIG_FRAME_POINTER
> -	while (n--)
> -		frame = frame->next_frame;
> +	while (n--) {
> +		if (probe_kernel_address(&frame->next_frame, frame))
> +			break;
> +	}
>  #endif
>  
>  	return (unsigned long)frame;

Thanks, no more crash :)

Tested-by: Eric Dumazet <eric.dumazet@gmail.com>