tracing, perf: Implement BPF programs attached to kprobes

BPF programs, attached to kprobes, provide a safe way to execute
user-defined BPF byte-code programs without being able to crash or
hang the kernel in any way. The BPF engine makes sure that such
programs have a finite execution time and that they cannot break
out of their sandbox.

The user interface is to attach to a kprobe via the perf syscall:

	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 the kprobe created.

Closing 'event_fd':

	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 the ring buffer.

Note, kprobes are a fundamentally _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.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1427312966-8434-4-git-send-email-ast@plumgrid.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

5 files changed, 204 insertions, 1 deletions

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 c40c2cac2d8e..5c13862d3e85 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"
 
@@ -3407,6 +3409,7 @@ 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)
 {
@@ -3416,6 +3419,7 @@ 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);
 }
 
@@ -3928,6 +3932,7 @@ 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)
 {
@@ -3981,6 +3986,9 @@ 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;
         }
@@ -6455,6 +6463,49 @@ 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)
@@ -6470,6 +6521,14 @@ 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;