Subject: Re: [PATCH v9 tip 3/9] tracing: attach BPF programs to kprobes

From: Masami Hiramatsu <[email-masked]>
Date: Sat, 21 Mar 2015 21:14:58 +0900

(2015/03/21 8:30), 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.
> 

Would you mean that the ABI of kprobe-based BPF programs? Kprobe API/ABIs
(register_kprobe() etc.) are stable, but the code who use kprobes certainly
depends the kernel binary by design. So, if you meant it, BPF programs must
be recompiled for every kernel binaries (including configuration changes,
not only its version).

Thank you,

> Signed-off-by: Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/[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..10ac48da4bb7
> --- /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]