linux-kernel - RE: [PATCH 1/2] perf probe: Prevent segfault when reading probe point with absolute address

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Date:	Wed, 26 Aug 2015 00:08:07 +0000
From:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
To:	"'Wang Nan'" <wangnan0@...wei.com>,
	"acme@...nel.org" <acme@...nel.org>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"pi3orama@....com" <pi3orama@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] perf probe: Prevent segfault when reading probe
 point with absolute address

> From: Wang Nan [mailto:wangnan0@...wei.com]
> 
> 'perf probe -l' panic if there is a manually inserted probing point
> with absolute address. For example:
> 
>  # echo 'p:probe/abs_ffffffff811e6615 0xffffffff811e6615' > /sys/kernel/debug/tracing/kprobe_events
>  # perf probe -l
>  Segmentation fault (core dumped)
> 
> This patch fix this problem by considering the situation that
> "tp->symbol == NULL" in find_perf_probe_point_from_dwarf() and
> find_perf_probe_point_from_map().

Oops, OK this is a bug.

Thanks!


Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>

> 
> After this patch:
> 
>  # perf probe -l
>  probe:abs_ffffffff811e6615 (on SyS_write+5@...read_write.c)
> 
> And when debug info is missing:
> 
>  # rm -rf ~/.debug
>  # mv /lib/modules/4.2.0-rc1+/build/vmlinux /lib/modules/4.2.0-rc1+/build/vmlinux.bak
>  # perf probe -l
>  probe:abs_ffffffff811e6615 (on sys_write+5)
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/probe-event.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index f07374b..6c7e538 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -515,7 +515,7 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
>  		if (ret < 0)
>  			goto error;
>  		addr += stext;
> -	} else {
> +	} else if (tp->symbol) {
>  		addr = kernel_get_symbol_address_by_name(tp->symbol, false);
>  		if (addr == 0)
>  			goto error;
> @@ -1815,17 +1815,17 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
>  {
>  	struct symbol *sym = NULL;
>  	struct map *map;
> -	u64 addr;
> +	u64 addr = tp->address;
>  	int ret = -ENOENT;
> 
>  	if (!is_kprobe) {
>  		map = dso__new_map(tp->module);
>  		if (!map)
>  			goto out;
> -		addr = tp->address;
>  		sym = map__find_symbol(map, addr, NULL);
>  	} else {
> -		addr = kernel_get_symbol_address_by_name(tp->symbol, true);
> +		if (tp->symbol)
> +			addr = kernel_get_symbol_address_by_name(tp->symbol, true);
>  		if (addr) {
>  			addr += tp->offset;
>  			sym = __find_kernel_function(addr, &map);
> --
> 1.8.3.4