1/* Copyright (c) 2011-2015 PLUMgrid, http://plumgrid.com
2 *
3 * This program is free software; you can redistribute it and/or
4 * modify it under the terms of version 2 of the GNU General Public
5 * License as published by the Free Software Foundation.
6 */
7#include <linux/kernel.h>
8#include <linux/types.h>
9#include <linux/slab.h>
10#include <linux/bpf.h>
11#include <linux/filter.h>
12#include <linux/uaccess.h>
13#include <linux/ctype.h>
14#include "trace.h"
15
16static DEFINE_PER_CPU(int, bpf_prog_active);
17
18/**
19 * trace_call_bpf - invoke BPF program
20 * @prog: BPF program
21 * @ctx: opaque context pointer
22 *
23 * kprobe handlers execute BPF programs via this helper.
24 * Can be used from static tracepoints in the future.
25 *
26 * Return: BPF programs always return an integer which is interpreted by
27 * kprobe handler as:
28 * 0 - return from kprobe (event is filtered out)
29 * 1 - store kprobe event into ring buffer
30 * Other values are reserved and currently alias to 1
31 */
32unsigned int trace_call_bpf(struct bpf_prog *prog, void *ctx)
33{
34	unsigned int ret;
35
36	if (in_nmi()) /* not supported yet */
37		return 1;
38
39	preempt_disable();
40
41	if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) {
42		/*
43		 * since some bpf program is already running on this cpu,
44		 * don't call into another bpf program (same or different)
45		 * and don't send kprobe event into ring-buffer,
46		 * so return zero here
47		 */
48		ret = 0;
49		goto out;
50	}
51
52	rcu_read_lock();
53	ret = BPF_PROG_RUN(prog, ctx);
54	rcu_read_unlock();
55
56 out:
57	__this_cpu_dec(bpf_prog_active);
58	preempt_enable();
59
60	return ret;
61}
62EXPORT_SYMBOL_GPL(trace_call_bpf);
63
64static u64 bpf_probe_read(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
65{
66	void *dst = (void *) (long) r1;
67	int size = (int) r2;
68	void *unsafe_ptr = (void *) (long) r3;
69
70	return probe_kernel_read(dst, unsafe_ptr, size);
71}
72
73static const struct bpf_func_proto bpf_probe_read_proto = {
74	.func		= bpf_probe_read,
75	.gpl_only	= true,
76	.ret_type	= RET_INTEGER,
77	.arg1_type	= ARG_PTR_TO_STACK,
78	.arg2_type	= ARG_CONST_STACK_SIZE,
79	.arg3_type	= ARG_ANYTHING,
80};
81
82static u64 bpf_ktime_get_ns(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
83{
84	/* NMI safe access to clock monotonic */
85	return ktime_get_mono_fast_ns();
86}
87
88static const struct bpf_func_proto bpf_ktime_get_ns_proto = {
89	.func		= bpf_ktime_get_ns,
90	.gpl_only	= true,
91	.ret_type	= RET_INTEGER,
92};
93
94/*
95 * limited trace_printk()
96 * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed
97 */
98static u64 bpf_trace_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5)
99{
100	char *fmt = (char *) (long) r1;
101	int mod[3] = {};
102	int fmt_cnt = 0;
103	int i;
104
105	/*
106	 * bpf_check()->check_func_arg()->check_stack_boundary()
107	 * guarantees that fmt points to bpf program stack,
108	 * fmt_size bytes of it were initialized and fmt_size > 0
109	 */
110	if (fmt[--fmt_size] != 0)
111		return -EINVAL;
112
113	/* check format string for allowed specifiers */
114	for (i = 0; i < fmt_size; i++) {
115		if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i]))
116			return -EINVAL;
117
118		if (fmt[i] != '%')
119			continue;
120
121		if (fmt_cnt >= 3)
122			return -EINVAL;
123
124		/* fmt[i] != 0 && fmt[last] == 0, so we can access fmt[i + 1] */
125		i++;
126		if (fmt[i] == 'l') {
127			mod[fmt_cnt]++;
128			i++;
129		} else if (fmt[i] == 'p') {
130			mod[fmt_cnt]++;
131			i++;
132			if (!isspace(fmt[i]) && !ispunct(fmt[i]) && fmt[i] != 0)
133				return -EINVAL;
134			fmt_cnt++;
135			continue;
136		}
137
138		if (fmt[i] == 'l') {
139			mod[fmt_cnt]++;
140			i++;
141		}
142
143		if (fmt[i] != 'd' && fmt[i] != 'u' && fmt[i] != 'x')
144			return -EINVAL;
145		fmt_cnt++;
146	}
147
148	return __trace_printk(1/* fake ip will not be printed */, fmt,
149			      mod[0] == 2 ? r3 : mod[0] == 1 ? (long) r3 : (u32) r3,
150			      mod[1] == 2 ? r4 : mod[1] == 1 ? (long) r4 : (u32) r4,
151			      mod[2] == 2 ? r5 : mod[2] == 1 ? (long) r5 : (u32) r5);
152}
153
154static const struct bpf_func_proto bpf_trace_printk_proto = {
155	.func		= bpf_trace_printk,
156	.gpl_only	= true,
157	.ret_type	= RET_INTEGER,
158	.arg1_type	= ARG_PTR_TO_STACK,
159	.arg2_type	= ARG_CONST_STACK_SIZE,
160};
161
162static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
163{
164	switch (func_id) {
165	case BPF_FUNC_map_lookup_elem:
166		return &bpf_map_lookup_elem_proto;
167	case BPF_FUNC_map_update_elem:
168		return &bpf_map_update_elem_proto;
169	case BPF_FUNC_map_delete_elem:
170		return &bpf_map_delete_elem_proto;
171	case BPF_FUNC_probe_read:
172		return &bpf_probe_read_proto;
173	case BPF_FUNC_ktime_get_ns:
174		return &bpf_ktime_get_ns_proto;
175
176	case BPF_FUNC_trace_printk:
177		/*
178		 * this program might be calling bpf_trace_printk,
179		 * so allocate per-cpu printk buffers
180		 */
181		trace_printk_init_buffers();
182
183		return &bpf_trace_printk_proto;
184	default:
185		return NULL;
186	}
187}
188
189/* bpf+kprobe programs can access fields of 'struct pt_regs' */
190static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type type)
191{
192	/* check bounds */
193	if (off < 0 || off >= sizeof(struct pt_regs))
194		return false;
195
196	/* only read is allowed */
197	if (type != BPF_READ)
198		return false;
199
200	/* disallow misaligned access */
201	if (off % size != 0)
202		return false;
203
204	return true;
205}
206
207static struct bpf_verifier_ops kprobe_prog_ops = {
208	.get_func_proto  = kprobe_prog_func_proto,
209	.is_valid_access = kprobe_prog_is_valid_access,
210};
211
212static struct bpf_prog_type_list kprobe_tl = {
213	.ops	= &kprobe_prog_ops,
214	.type	= BPF_PROG_TYPE_KPROBE,
215};
216
217static int __init register_kprobe_prog_ops(void)
218{
219	bpf_register_prog_type(&kprobe_tl);
220	return 0;
221}
222late_initcall(register_kprobe_prog_ops);
223