kernel/trace/bpf_trace.c

   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
  16 static 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  */
  32 unsigned 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 }
  62 EXPORT_SYMBOL_GPL(trace_call_bpf);
  63
  64 static 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
  73 static 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
  82 /*
  83  * limited trace_printk()
  84  * only %d %u %x %ld %lu %lx %lld %llu %llx %p conversion specifiers allowed
  85  */
  86 static u64 bpf_trace_printk(u64 r1, u64 fmt_size, u64 r3, u64 r4, u64 r5)
  87 {
  88         char *fmt = (char *) (long) r1;
  89         int mod[3] = {};
  90         int fmt_cnt = 0;
  91         int i;
  92
  93         /*
  94          * bpf_check()->check_func_arg()->check_stack_boundary()
  95          * guarantees that fmt points to bpf program stack,
  96          * fmt_size bytes of it were initialized and fmt_size > 0
  97          */
  98         if (fmt[--fmt_size] != 0)
  99                 return -EINVAL;
 100
 101         /* check format string for allowed specifiers */
 102         for (i = 0; i < fmt_size; i++) {
 103                 if ((!isprint(fmt[i]) && !isspace(fmt[i])) || !isascii(fmt[i]))
 104                         return -EINVAL;
 105
 106                 if (fmt[i] != '%')
 107                         continue;
 108
 109                 if (fmt_cnt >= 3)
 110                         return -EINVAL;
 111
 112                 /* fmt[i] != 0 && fmt[last] == 0, so we can access fmt[i + 1] */
 113                 i++;
 114                 if (fmt[i] == 'l') {
 115                         mod[fmt_cnt]++;
 116                         i++;
 117                 } else if (fmt[i] == 'p') {
 118                         mod[fmt_cnt]++;
 119                         i++;
 120                         if (!isspace(fmt[i]) && !ispunct(fmt[i]) && fmt[i] != 0)
 121                                 return -EINVAL;
 122                         fmt_cnt++;
 123                         continue;
 124                 }
 125
 126                 if (fmt[i] == 'l') {
 127                         mod[fmt_cnt]++;
 128                         i++;
 129                 }
 130
 131                 if (fmt[i] != 'd' && fmt[i] != 'u' && fmt[i] != 'x')
 132                         return -EINVAL;
 133                 fmt_cnt++;
 134         }
 135
 136         return __trace_printk(1/* fake ip will not be printed */, fmt,
 137                               mod[0] == 2 ? r3 : mod[0] == 1 ? (long) r3 : (u32) r3,
 138                               mod[1] == 2 ? r4 : mod[1] == 1 ? (long) r4 : (u32) r4,
 139                               mod[2] == 2 ? r5 : mod[2] == 1 ? (long) r5 : (u32) r5);
 140 }
 141
 142 static const struct bpf_func_proto bpf_trace_printk_proto = {
 143         .func           = bpf_trace_printk,
 144         .gpl_only       = true,
 145         .ret_type       = RET_INTEGER,
 146         .arg1_type      = ARG_PTR_TO_STACK,
 147         .arg2_type      = ARG_CONST_STACK_SIZE,
 148 };
 149
 150 const struct bpf_func_proto *bpf_get_trace_printk_proto(void)
 151 {
 152         /*
 153          * this program might be calling bpf_trace_printk,
 154          * so allocate per-cpu printk buffers
 155          */
 156         trace_printk_init_buffers();
 157
 158         return &bpf_trace_printk_proto;
 159 }
 160
 161 static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
 162 {
 163         switch (func_id) {
 164         case BPF_FUNC_map_lookup_elem:
 165                 return &bpf_map_lookup_elem_proto;
 166         case BPF_FUNC_map_update_elem:
 167                 return &bpf_map_update_elem_proto;
 168         case BPF_FUNC_map_delete_elem:
 169                 return &bpf_map_delete_elem_proto;
 170         case BPF_FUNC_probe_read:
 171                 return &bpf_probe_read_proto;
 172         case BPF_FUNC_ktime_get_ns:
 173                 return &bpf_ktime_get_ns_proto;
 174         case BPF_FUNC_tail_call:
 175                 return &bpf_tail_call_proto;
 176         case BPF_FUNC_get_current_pid_tgid:
 177                 return &bpf_get_current_pid_tgid_proto;
 178         case BPF_FUNC_get_current_uid_gid:
 179                 return &bpf_get_current_uid_gid_proto;
 180         case BPF_FUNC_get_current_comm:
 181                 return &bpf_get_current_comm_proto;
 182         case BPF_FUNC_trace_printk:
 183                 return bpf_get_trace_printk_proto();
 184         case BPF_FUNC_get_smp_processor_id:
 185                 return &bpf_get_smp_processor_id_proto;
 186         default:
 187                 return NULL;
 188         }
 189 }
 190
 191 /* bpf+kprobe programs can access fields of 'struct pt_regs' */
 192 static bool kprobe_prog_is_valid_access(int off, int size, enum bpf_access_type type)
 193 {
 194         /* check bounds */
 195         if (off < 0 || off >= sizeof(struct pt_regs))
 196                 return false;
 197
 198         /* only read is allowed */
 199         if (type != BPF_READ)
 200                 return false;
 201
 202         /* disallow misaligned access */
 203         if (off % size != 0)
 204                 return false;
 205
 206         return true;
 207 }
 208
 209 static struct bpf_verifier_ops kprobe_prog_ops = {
 210         .get_func_proto  = kprobe_prog_func_proto,
 211         .is_valid_access = kprobe_prog_is_valid_access,
 212 };
 213
 214 static struct bpf_prog_type_list kprobe_tl = {
 215         .ops    = &kprobe_prog_ops,
 216         .type   = BPF_PROG_TYPE_KPROBE,
 217 };
 218
 219 static int __init register_kprobe_prog_ops(void)
 220 {
 221         bpf_register_prog_type(&kprobe_tl);
 222         return 0;
 223 }
 224 late_initcall(register_kprobe_prog_ops);