Subject: Re: [PATCH v10 tip 3/9] tracing: attach BPF programs to kprobes

From: Masami Hiramatsu <[email-masked]>
Date: Mon, 23 Mar 2015 11:14:58 +0900

(2015/03/23 4:39), Alexei Starovoitov wrote:
> User interface:
> struct perf_event_attr attr = {.type = PERF_TYPE_TRACEPOINT, .config = event_id, ...};
> event_fd = perf_event_open(&attr,...);
> ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
> 
> prog_fd is a file descriptor associated with BPF program previously loaded.
> event_id is an ID of created kprobe
> 
> close(event_fd) - automatically detaches BPF program from it
> 
> BPF programs can call in-kernel helper functions to:
> - lookup/update/delete elements in maps
> - probe_read - wraper of probe_kernel_read() used to access any kernel
>   data structures
> 
> BPF programs receive 'struct pt_regs *' as an input
> ('struct pt_regs' is architecture dependent)
> and return 0 to ignore the event and 1 to store kprobe event into ring buffer.
> 
> Note, kprobes are _not_ a stable kernel ABI, so bpf programs attached to
> kprobes must be recompiled for every kernel version and user must supply correct
> LINUX_VERSION_CODE in attr.kern_version during bpf_prog_load() call.
> 

This looks OK to me :)

Reviewed-by: Masami Hiramatsu <[email-masked]>

Thanks!

> Signed-off-by: Alexei Starovoitov <[email-masked]>
> Reviewed-by: Steven Rostedt <[email-masked]>
> ---
>  include/linux/ftrace_event.h    |   11 ++++
>  include/uapi/linux/bpf.h        |    3 +
>  include/uapi/linux/perf_event.h |    1 +
>  kernel/bpf/syscall.c            |    7 ++-
>  kernel/events/core.c            |   59 ++++++++++++++++++
>  kernel/trace/Makefile           |    1 +
>  kernel/trace/bpf_trace.c        |  130 +++++++++++++++++++++++++++++++++++++++
>  kernel/trace/trace_kprobe.c     |    8 +++
>  8 files changed, 219 insertions(+), 1 deletion(-)
>  create mode 100644 kernel/trace/bpf_trace.c
> 
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index 77325e1a1816..0aa535bc9f05 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -13,6 +13,7 @@ struct trace_array;
>  struct trace_buffer;
>  struct tracer;
>  struct dentry;
> +struct bpf_prog;
>  
>  struct trace_print_flags {
>  	unsigned long		mask;
> @@ -306,6 +307,7 @@ struct ftrace_event_call {
>  #ifdef CONFIG_PERF_EVENTS
>  	int				perf_refcount;
>  	struct hlist_head __percpu	*perf_events;
> +	struct bpf_prog			*prog;
>  
>  	int	(*perf_perm)(struct ftrace_event_call *,
>  			     struct perf_event *);
> @@ -551,6 +553,15 @@ event_trigger_unlock_commit_regs(struct ftrace_event_file *file,
>  		event_triggers_post_call(file, tt);
>  }
>  
> +#ifdef CONFIG_BPF_SYSCALL
> +unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx);
> +#else
> +static inline unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
> +{
> +	return 1;
> +}
> +#endif
> +
>  enum {
>  	FILTER_OTHER = 0,
>  	FILTER_STATIC_STRING,
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 45da7ec7d274..b2948feeb70b 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -118,6 +118,7 @@ enum bpf_map_type {
>  enum bpf_prog_type {
>  	BPF_PROG_TYPE_UNSPEC,
>  	BPF_PROG_TYPE_SOCKET_FILTER,
> +	BPF_PROG_TYPE_KPROBE,
>  };
>  
>  /* flags for BPF_MAP_UPDATE_ELEM command */
> @@ -151,6 +152,7 @@ union bpf_attr {
>  		__u32		log_level;	/* verbosity level of verifier */
>  		__u32		log_size;	/* size of user buffer */
>  		__aligned_u64	log_buf;	/* user supplied buffer */
> +		__u32		kern_version;	/* checked when prog_type=kprobe */
>  	};
>  } __attribute__((aligned(8)));
>  
> @@ -162,6 +164,7 @@ enum bpf_func_id {
>  	BPF_FUNC_map_lookup_elem, /* void *map_lookup_elem(&map, &key) */
>  	BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
>  	BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
> +	BPF_FUNC_probe_read,      /* int bpf_probe_read(void *dst, int size, void *src) */
>  	__BPF_FUNC_MAX_ID,
>  };
>  
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 3c8b45de57ec..ad4dade2a502 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -382,6 +382,7 @@ struct perf_event_attr {
>  #define PERF_EVENT_IOC_SET_OUTPUT	_IO ('$', 5)
>  #define PERF_EVENT_IOC_SET_FILTER	_IOW('$', 6, char *)
>  #define PERF_EVENT_IOC_ID		_IOR('$', 7, __u64 *)
> +#define PERF_EVENT_IOC_SET_BPF		_IOW('$', 8, __u32)
>  
>  enum perf_event_ioc_flags {
>  	PERF_IOC_FLAG_GROUP		= 1U << 0,
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 536edc2be307..504c10b990ef 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -16,6 +16,7 @@
>  #include <linux/file.h>
>  #include <linux/license.h>
>  #include <linux/filter.h>
> +#include <linux/version.h>
>  
>  static LIST_HEAD(bpf_map_types);
>  
> @@ -467,7 +468,7 @@ struct bpf_prog *bpf_prog_get(u32 ufd)
>  }
>  
>  /* last field in 'union bpf_attr' used by this command */
> -#define	BPF_PROG_LOAD_LAST_FIELD log_buf
> +#define	BPF_PROG_LOAD_LAST_FIELD kern_version
>  
>  static int bpf_prog_load(union bpf_attr *attr)
>  {
> @@ -492,6 +493,10 @@ static int bpf_prog_load(union bpf_attr *attr)
>  	if (attr->insn_cnt >= BPF_MAXINSNS)
>  		return -EINVAL;
>  
> +	if (type == BPF_PROG_TYPE_KPROBE &&
> +	    attr->kern_version != LINUX_VERSION_CODE)
> +		return -EINVAL;
> +
>  	/* plain bpf_prog allocation */
>  	prog = bpf_prog_alloc(bpf_prog_size(attr->insn_cnt), GFP_USER);
>  	if (!prog)
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 2709063eb26b..3a45e7f6b2df 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -42,6 +42,8 @@
>  #include <linux/module.h>
>  #include <linux/mman.h>
>  #include <linux/compat.h>
> +#include <linux/bpf.h>
> +#include <linux/filter.h>
>  
>  #include "internal.h"
>  
> @@ -3402,6 +3404,7 @@ errout:
>  }
>  
>  static void perf_event_free_filter(struct perf_event *event);
> +static void perf_event_free_bpf_prog(struct perf_event *event);
>  
>  static void free_event_rcu(struct rcu_head *head)
>  {
> @@ -3411,6 +3414,7 @@ static void free_event_rcu(struct rcu_head *head)
>  	if (event->ns)
>  		put_pid_ns(event->ns);
>  	perf_event_free_filter(event);
> +	perf_event_free_bpf_prog(event);
>  	kfree(event);
>  }
>  
> @@ -3923,6 +3927,7 @@ static inline int perf_fget_light(int fd, struct fd *p)
>  static int perf_event_set_output(struct perf_event *event,
>  				 struct perf_event *output_event);
>  static int perf_event_set_filter(struct perf_event *event, void __user *arg);
> +static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd);
>  
>  static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned long arg)
>  {
> @@ -3976,6 +3981,9 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
>  	case PERF_EVENT_IOC_SET_FILTER:
>  		return perf_event_set_filter(event, (void __user *)arg);
>  
> +	case PERF_EVENT_IOC_SET_BPF:
> +		return perf_event_set_bpf_prog(event, arg);
> +
>  	default:
>  		return -ENOTTY;
>  	}
> @@ -6436,6 +6444,49 @@ static void perf_event_free_filter(struct perf_event *event)
>  	ftrace_profile_free_filter(event);
>  }
>  
> +static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
> +{
> +	struct bpf_prog *prog;
> +
> +	if (event->attr.type != PERF_TYPE_TRACEPOINT)
> +		return -EINVAL;
> +
> +	if (event->tp_event->prog)
> +		return -EEXIST;
> +
> +	if (!(event->tp_event->flags & TRACE_EVENT_FL_KPROBE))
> +		/* bpf programs can only be attached to kprobes */
> +		return -EINVAL;
> +
> +	prog = bpf_prog_get(prog_fd);
> +	if (IS_ERR(prog))
> +		return PTR_ERR(prog);
> +
> +	if (prog->aux->prog_type != BPF_PROG_TYPE_KPROBE) {
> +		/* valid fd, but invalid bpf program type */
> +		bpf_prog_put(prog);
> +		return -EINVAL;
> +	}
> +
> +	event->tp_event->prog = prog;
> +
> +	return 0;
> +}
> +
> +static void perf_event_free_bpf_prog(struct perf_event *event)
> +{
> +	struct bpf_prog *prog;
> +
> +	if (!event->tp_event)
> +		return;
> +
> +	prog = event->tp_event->prog;
> +	if (prog) {
> +		event->tp_event->prog = NULL;
> +		bpf_prog_put(prog);
> +	}
> +}
> +
>  #else
>  
>  static inline void perf_tp_register(void)
> @@ -6451,6 +6502,14 @@ static void perf_event_free_filter(struct perf_event *event)
>  {
>  }
>  
> +static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
> +{
> +	return -ENOENT;
> +}
> +
> +static void perf_event_free_bpf_prog(struct perf_event *event)
> +{
> +}
>  #endif /* CONFIG_EVENT_TRACING */
>  
>  #ifdef CONFIG_HAVE_HW_BREAKPOINT
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index 98f26588255e..c575a300103b 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -53,6 +53,7 @@ obj-$(CONFIG_EVENT_TRACING) += trace_event_perf.o
>  endif
>  obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
>  obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
> +obj-$(CONFIG_BPF_SYSCALL) += bpf_trace.o
>  obj-$(CONFIG_KPROBE_EVENT) += trace_kprobe.o
>  obj-$(CONFIG_TRACEPOINTS) += power-traces.o
>  ifeq ($(CONFIG_PM),y)
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> new file mode 100644
> index 000000000000..f1e87da91da3
> --- /dev/null
> +++ b/kernel/trace/bpf_trace.c
> @@ -0,0 +1,130 @@
> +/* Copyright (c) 2011-2015 PLUMgrid, http://plumgrid.com
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of version 2 of the GNU General Public
> + * License as published by the Free Software Foundation.
> + */
> +#include <linux/kernel.h>
> +#include <linux/types.h>
> +#include <linux/slab.h>
> +#include <linux/bpf.h>
> +#include <linux/filter.h>
> +#include <linux/uaccess.h>
> +#include "trace.h"
> +
> +static DEFINE_PER_CPU(int, bpf_prog_active);
> +
> +/**
> + * trace_call_bpf - invoke BPF program
> + * @prog: BPF program
> + * @ctx: opaque context pointer
> + *
> + * kprobe handlers execute BPF programs via this helper.
> + * Can be used from static tracepoints in the future.
> + *
> + * Return: BPF programs always return an integer which is interpreted by
> + * kprobe handler as:
> + * 0 - return from kprobe (event is filtered out)
> + * 1 - store kprobe event into ring buffer
> + * Other values are reserved and currently alias to 1
> + */
> +unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
> +{
> +	unsigned int ret;
> +
> +	if (in_nmi()) /* not supported yet */
> +		return 1;
> +
> +	preempt_disable();
> +
> +	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) {
> +		/*
> +		 * since some bpf program is already running on this cpu,
> +		 * don't call into another bpf program (same or different)
> +		 * and don't send kprobe event into ring-buffer,
> +		 * so return zero here
> +		 */
> +		ret = 0;
> +		goto out;
> +	}
> +
> +	rcu_read_lock();
> +	ret = BPF_PROG_RUN(prog, ctx);
> +	rcu_read_unlock();
> +
> + out:
> +	__this_cpu_dec(bpf_prog_active);
> +	preempt_enable();
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(trace_call_bpf);
> +
> +static u64 bpf_probe_read(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
> +{
> +	void *dst = (void *) (long) r1;
> +	int size = (int) r2;
> +	void *unsafe_ptr = (void *) (long) r3;
> +
> +	return probe_kernel_read(dst, unsafe_ptr, size);
> +}
> +
> +static const struct bpf_func_proto bpf_probe_read_proto = {
> +	.func		= bpf_probe_read,
> +	.gpl_only	= true,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_STACK,
> +	.arg2_type	= ARG_CONST_STACK_SIZE,
> +	.arg3_type	= ARG_ANYTHING,
> +};
> +
> +static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
> +{
> +	switch (func_id) {
> +	case BPF_FUNC_map_lookup_elem:
> +		return &bpf_map_lookup_elem_proto;
> +	case BPF_FUNC_map_update_elem:
> +		return &bpf_map_update_elem_proto;
> +	case BPF_FUNC_map_delete_elem:
> +		return &bpf_map_delete_elem_proto;
> +	case BPF_FUNC_probe_read:
> +		return &bpf_probe_read_proto;
> +	default:
> +		return NULL;
> +	}
> +}
> +
> +/* bpf+kprobe programs can access fields of 'struct pt_regs' */
> +static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type type)
> +{
> +	/* check bounds */
> +	if (off < 0 || off >= sizeof(struct pt_regs))
> +		return false;
> +
> +	/* only read is allowed */
> +	if (type != BPF_READ)
> +		return false;
> +
> +	/* disallow misaligned access */
> +	if (off % size != 0)
> +		return false;
> +
> +	return true;
> +}
> +
> +static struct bpf_verifier_ops kprobe_prog_ops = {
> +	.get_func_proto  = kprobe_prog_func_proto,
> +	.is_valid_access = kprobe_prog_is_valid_access,
> +};
> +
> +static struct bpf_prog_type_list kprobe_tl = {
> +	.ops	= &kprobe_prog_ops,
> +	.type	= BPF_PROG_TYPE_KPROBE,
> +};
> +
> +static int __init register_kprobe_prog_ops(void)
> +{
> +	bpf_register_prog_type(&kprobe_tl);
> +	return 0;
> +}
> +late_initcall(register_kprobe_prog_ops);
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 8fa549f6f528..dc3462507d7c 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1134,11 +1134,15 @@ static void
>  kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
>  {
>  	struct ftrace_event_call *call = &tk->tp.call;
> +	struct bpf_prog *prog = call->prog;
>  	struct kprobe_trace_entry_head *entry;
>  	struct hlist_head *head;
>  	int size, __size, dsize;
>  	int rctx;
>  
> +	if (prog && !trace_call_bpf(prog, regs))
> +		return;
> +
>  	head = this_cpu_ptr(call->perf_events);
>  	if (hlist_empty(head))
>  		return;
> @@ -1165,11 +1169,15 @@ kretprobe_perf_func(struct trace_kprobe *tk, struct kretprobe_instance *ri,
>  		    struct pt_regs *regs)
>  {
>  	struct ftrace_event_call *call = &tk->tp.call;
> +	struct bpf_prog *prog = call->prog;
>  	struct kretprobe_trace_entry_head *entry;
>  	struct hlist_head *head;
>  	int size, __size, dsize;
>  	int rctx;
>  
> +	if (prog && !trace_call_bpf(prog, regs))
> +		return;
> +
>  	head = this_cpu_ptr(call->perf_events);
>  	if (hlist_empty(head))
>  		return;
> 

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email-masked]