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Date: Thu, 30 Jul 2015 01:30:17 +0200
From: Daniel Borkmann <daniel@...earbox.net>
To: Kaixu Xia <xiakaixu@...wei.com>, ast@...mgrid.com,
davem@...emloft.net, acme@...nel.org, mingo@...hat.com,
a.p.zijlstra@...llo.nl, masami.hiramatsu.pt@...achi.com,
jolsa@...nel.org
CC: wangnan0@...wei.com, linux-kernel@...r.kernel.org,
pi3orama@....com, hekuang@...wei.com
Subject: Re: [PATCH v4 2/4] bpf: Add new bpf map type to store the pointer
to struct perf_event
On 07/28/2015 01:17 PM, Kaixu Xia wrote:
> Introduce a new bpf map type 'BPF_MAP_TYPE_PERF_EVENT_ARRAY'.
> This map only stores the pointer to struct perf_event. The
> user space event FDs from perf_event_open() syscall are converted
> to the pointer to struct perf_event and stored in map.
>
> Signed-off-by: Kaixu Xia <xiakaixu@...wei.com>
> ---
> include/linux/bpf.h | 1 +
> include/linux/perf_event.h | 2 ++
> include/uapi/linux/bpf.h | 1 +
> kernel/bpf/arraymap.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++
> kernel/bpf/verifier.c | 15 ++++++++++++
> kernel/events/core.c | 17 ++++++++++++++
> 6 files changed, 93 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 610b730..3c9c0eb 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -10,6 +10,7 @@
> #include <uapi/linux/bpf.h>
> #include <linux/workqueue.h>
> #include <linux/file.h>
> +#include <linux/perf_event.h>
>
> struct bpf_map;
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 2027809..2ea4067 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -641,6 +641,7 @@ extern int perf_event_init_task(struct task_struct *child);
> extern void perf_event_exit_task(struct task_struct *child);
> extern void perf_event_free_task(struct task_struct *task);
> extern void perf_event_delayed_put(struct task_struct *task);
> +extern struct perf_event *perf_event_get(unsigned int fd);
> extern void perf_event_print_debug(void);
> extern void perf_pmu_disable(struct pmu *pmu);
> extern void perf_pmu_enable(struct pmu *pmu);
> @@ -979,6 +980,7 @@ static inline int perf_event_init_task(struct task_struct *child) { return 0; }
> static inline void perf_event_exit_task(struct task_struct *child) { }
> static inline void perf_event_free_task(struct task_struct *task) { }
> static inline void perf_event_delayed_put(struct task_struct *task) { }
> +static struct perf_event *perf_event_get(unsigned int fd) { return NULL; }
> static inline void perf_event_print_debug(void) { }
> static inline int perf_event_task_disable(void) { return -EINVAL; }
> static inline int perf_event_task_enable(void) { return -EINVAL; }
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 29ef6f9..69a1f6b 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -114,6 +114,7 @@ enum bpf_map_type {
> BPF_MAP_TYPE_HASH,
> BPF_MAP_TYPE_ARRAY,
> BPF_MAP_TYPE_PROG_ARRAY,
> + BPF_MAP_TYPE_PERF_EVENT_ARRAY,
> };
>
> enum bpf_prog_type {
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index 4784cdc..a9e0235 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -297,3 +297,60 @@ static int __init register_prog_array_map(void)
> return 0;
> }
> late_initcall(register_prog_array_map);
> +
> +static void *perf_event_fd_array_get_ptr(struct bpf_array *array, int fd)
> +{
> + struct perf_event *event;
> +
> + event = perf_event_get(fd);
> + if (IS_ERR(event))
> + return event;
So in case of !CONFIG_PERF_EVENTS, you define perf_event_get() to return NULL.
Seems like this will give a nice NULL ptr deref below. ;)
> + /*
> + * prevent some crazy events so we can make our life easier
> + */
> + if (event->attr.type != PERF_TYPE_RAW &&
> + event->attr.type != PERF_TYPE_HARDWARE) {
> + perf_event_release_kernel(event);
> + return ERR_PTR(-EINVAL);
> + }
> + return event;
> +}
> +
> +static void perf_event_fd_array_put_ptr(struct bpf_array *array, void *ptr)
> +{
> + struct perf_event *event = (struct perf_event *)ptr;
( Same comment as in previous patch. )
> + perf_event_release_kernel(event);
> +}
> +
> +static const struct fd_array_map_ops perf_event_fd_array_map_ops = {
> + .get_ptr = perf_event_fd_array_get_ptr,
> + .put_ptr = perf_event_fd_array_put_ptr,
> +};
...
> +late_initcall(register_perf_event_array_map);
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 039d866..c70f7e7 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -924,6 +924,21 @@ static int check_call(struct verifier_env *env, int func_id)
> */
> return -EINVAL;
>
> + if (map && map->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY &&
> + func_id != BPF_FUNC_perf_event_read)
> + /* perf_event_array map type needs extra care:
> + * only allow to pass it into bpf_perf_event_read() for now.
> + * bpf_map_update/delete_elem() must only be done via syscall
> + */
> + return -EINVAL;
> +
> + if (func_id == BPF_FUNC_perf_event_read &&
> + map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
> + /* don't allow any other map type to be passed into
> + * bpf_perf_event_read()
> + */
> + return -EINVAL;
Maybe a function as we do similar checks with BPF_MAP_TYPE_PROG_ARRAY?
> return 0;
> }
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index d3dae34..58f0d47 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -8574,6 +8574,23 @@ void perf_event_delayed_put(struct task_struct *task)
> WARN_ON_ONCE(task->perf_event_ctxp[ctxn]);
> }
>
> +struct perf_event *perf_event_get(unsigned int fd)
> +{
> + int err;
> + struct fd f;
> + struct perf_event *event;
> +
> + err = perf_fget_light(fd, &f);
> + if (err)
> + return ERR_PTR(err);
> +
> + event = f.file->private_data;
> + atomic_long_inc(&event->refcount);
> + fdput(f);
> +
> + return event;
> +}
> +
> /*
> * inherit a event from parent task to child task:
> */
>
--
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