linux-kernel - Re: [PATCH v2] perf tools: perf_event_paranoid and kptr

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Date:   Thu, 25 Feb 2021 17:11:10 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Jackie Liu <jackieliu2113@...il.com>
Cc:     linux-kernel@...r.kernel.org, Jackie Liu <liuyun01@...inos.cn>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v2] perf tools: perf_event_paranoid and kptr_restrict may
 crash on 'perf top'

On Thu, Feb 25, 2021 at 02:25:30PM +0800, Jackie Liu wrote:
> After install the libelf-dev package and compiling perf, kptr_restrict=2
> and perf_event_paranoid=3 will cause perf top to crash, because the
> value of /proc/kallsyms cannot be obtained, which leads to
> info->jited_ksyms == NULL. In order to solve this problem, Add a
> judgment before use.
> 
> Suggested-by: Jiri Olsa <jolsa@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Signed-off-by: Jackie Liu <liuyun01@...inos.cn>
> ---
>  tools/perf/util/bpf-event.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/perf/util/bpf-event.c b/tools/perf/util/bpf-event.c
> index 57d58c81a5f8..b1ce2d189d37 100644
> --- a/tools/perf/util/bpf-event.c
> +++ b/tools/perf/util/bpf-event.c
> @@ -225,6 +225,11 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_session *session,
>  		perf_env__fetch_btf(env, info->btf_id, btf);
>  	}
>  
> +	if (!info->jited_ksyms) {
> +		err = -1;
> +		goto out;
> +	}
> +

I think this check should be moved above, right after line:

        info = &info_linear->info;

so we don't do those extra btf checks

thanks,
jirka

>  	/* Synthesize PERF_RECORD_KSYMBOL */
>  	for (i = 0; i < sub_prog_cnt; i++) {
>  		__u32 *prog_lens = (__u32 *)(uintptr_t)(info->jited_func_lens);
> -- 
> 2.25.1
>