linux-kernel - Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf

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Message-ID: <20150717113729.GL12596@twins.programming.kicks-ass.net>
Date:	Fri, 17 Jul 2015 13:37:29 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	kaixu xia <xiakaixu@...wei.com>
Cc:	ast@...mgrid.com, davem@...emloft.net, acme@...nel.org,
	mingo@...hat.com, masami.hiramatsu.pt@...achi.com,
	jolsa@...nel.org, wangnan0@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com, hekuang@...wei.com
Subject: Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map

On Fri, Jul 17, 2015 at 06:43:33PM +0800, kaixu xia wrote:
> +static int replace_map_with_perf_event(void *value)
> +{
> +	struct perf_event *event;
> +	u32 fd;
> +
> +	fd = *(u32 *)value;
> +
> +	event = perf_event_get(fd);
> +	if (IS_ERR(event))
> +		return PTR_ERR(event);
> +

And userspace closes here,

> +	if (atomic_long_inc_not_zero(&event->refcount))

And this goes *BOOM*

> +		memcpy(value, &event, sizeof(struct perf_event *));
> +	else
> +		return -ENOENT;
> +
> +	return 0;
> +}

Also, why do you think its OK to prod around the internals of perf_event
outside of kernel/events/ ?
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