linux-kernel - Re: [PATCH 2/2] perf record: Fix crash when kptr is restricted

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Message-ID: <20160524124126.GR8897@kernel.org>
Date:	Tue, 24 May 2016 09:41:26 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	pi3orama@....com, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Zefan Li <lizefan@...wei.com>
Subject: Re: [PATCH 2/2] perf record: Fix crash when kptr is restricted

Em Tue, May 24, 2016 at 09:21:28AM +0000, Wang Nan escreveu:
> Before this patch, a simple 'perf record' could fail if kptr_restrict
> is set to 1 (for normal user) or 2 (for root):
> 
>  # perf record ls
>  WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted,
>  check /proc/sys/kernel/kptr_restrict.
> 
>  Samples in kernel functions may not be resolved if a suitable vmlinux
>  file is not found in the buildid cache or in the vmlinux path.
> 
>  Samples in kernel modules won't be resolved at all.
> 
>  If some relocation was applied (e.g. kexec) symbols may be misresolved
>  even with a suitable vmlinux or kallsyms file.
> 
>  Segmentation fault (core dumped)
> 
> This patch skips perf_event__synthesize_kernel_mmap() when kptr is not
> available.
> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>

Thanks, applied and added a:

Fixes: 45e90056904b ("perf machine: Do not bail out if not managing to read ref reloc symbol")

But I'll investigate a bit more later, as the patch fixes the problem,
but I think probably it'd be better to check what is not being set up
in the ref reloc symbol stuff not bailed out by the patch above.

- Arnaldo

> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> ---
>  tools/perf/util/event.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index f6fcc68..9b141f1 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -673,6 +673,8 @@ int perf_event__synthesize_kernel_mmap(struct perf_tool *tool,
>  	int err;
>  	union perf_event *event;
>  
> +	if (symbol_conf.kptr_restrict)
> +		return -1;
>  	if (map == NULL)
>  		return -1;
>  
> -- 
> 1.8.3.4