Date: Fri, 17 Jul 2015 13:37:29 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: kaixu xia <xiakaixu@huawei.com>
Cc: ast@plumgrid.com, davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
        masami.hiramatsu.pt@hitachi.com, jolsa@kernel.org, wangnan0@huawei.com,
        linux-kernel@vger.kernel.org, pi3orama@163.com, hekuang@huawei.com
Subject: Re: [RFC PATCH 3/6] bpf: Save the pointer to struct perf_event to map
Message-ID: <20150717113729.GL12596@twins.programming.kicks-ass.net>
References: <1437129816-13176-1-git-send-email-xiakaixu@huawei.com>
 <1437129816-13176-4-git-send-email-xiakaixu@huawei.com>
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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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