1 // SPDX-License-Identifier: GPL-2.0-only 2 /* Copyright (c) 2019 Facebook */ 3 #include <linux/hash.h> 4 #include <linux/bpf.h> 5 #include <linux/filter.h> 6 7 /* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */ 8 #define TRAMPOLINE_HASH_BITS 10 9 #define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS) 10 11 static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE]; 12 13 /* serializes access to trampoline_table */ 14 static DEFINE_MUTEX(trampoline_mutex); 15 16 struct bpf_trampoline *bpf_trampoline_lookup(u64 key) 17 { 18 struct bpf_trampoline *tr; 19 struct hlist_head *head; 20 void *image; 21 int i; 22 23 mutex_lock(&trampoline_mutex); 24 head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)]; 25 hlist_for_each_entry(tr, head, hlist) { 26 if (tr->key == key) { 27 refcount_inc(&tr->refcnt); 28 goto out; 29 } 30 } 31 tr = kzalloc(sizeof(*tr), GFP_KERNEL); 32 if (!tr) 33 goto out; 34 35 /* is_root was checked earlier. No need for bpf_jit_charge_modmem() */ 36 image = bpf_jit_alloc_exec(PAGE_SIZE); 37 if (!image) { 38 kfree(tr); 39 tr = NULL; 40 goto out; 41 } 42 43 tr->key = key; 44 INIT_HLIST_NODE(&tr->hlist); 45 hlist_add_head(&tr->hlist, head); 46 refcount_set(&tr->refcnt, 1); 47 mutex_init(&tr->mutex); 48 for (i = 0; i < BPF_TRAMP_MAX; i++) 49 INIT_HLIST_HEAD(&tr->progs_hlist[i]); 50 51 set_vm_flush_reset_perms(image); 52 /* Keep image as writeable. The alternative is to keep flipping ro/rw 53 * everytime new program is attached or detached. 54 */ 55 set_memory_x((long)image, 1); 56 tr->image = image; 57 out: 58 mutex_unlock(&trampoline_mutex); 59 return tr; 60 } 61 62 /* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50 63 * bytes on x86. Pick a number to fit into PAGE_SIZE / 2 64 */ 65 #define BPF_MAX_TRAMP_PROGS 40 66 67 static int bpf_trampoline_update(struct bpf_trampoline *tr) 68 { 69 void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2; 70 void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2; 71 struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS]; 72 int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY]; 73 int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT]; 74 struct bpf_prog **progs, **fentry, **fexit; 75 u32 flags = BPF_TRAMP_F_RESTORE_REGS; 76 struct bpf_prog_aux *aux; 77 int err; 78 79 if (fentry_cnt + fexit_cnt == 0) { 80 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL, 81 old_image, NULL); 82 tr->selector = 0; 83 goto out; 84 } 85 86 /* populate fentry progs */ 87 fentry = progs = progs_to_run; 88 hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist) 89 *progs++ = aux->prog; 90 91 /* populate fexit progs */ 92 fexit = progs; 93 hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist) 94 *progs++ = aux->prog; 95 96 if (fexit_cnt) 97 flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; 98 99 err = arch_prepare_bpf_trampoline(new_image, &tr->func.model, flags, 100 fentry, fentry_cnt, 101 fexit, fexit_cnt, 102 tr->func.addr); 103 if (err) 104 goto out; 105 106 if (tr->selector) 107 /* progs already running at this address */ 108 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL, 109 old_image, new_image); 110 else 111 /* first time registering */ 112 err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL, NULL, 113 new_image); 114 if (err) 115 goto out; 116 tr->selector++; 117 out: 118 return err; 119 } 120 121 static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t) 122 { 123 switch (t) { 124 case BPF_TRACE_FENTRY: 125 return BPF_TRAMP_FENTRY; 126 default: 127 return BPF_TRAMP_FEXIT; 128 } 129 } 130 131 int bpf_trampoline_link_prog(struct bpf_prog *prog) 132 { 133 enum bpf_tramp_prog_type kind; 134 struct bpf_trampoline *tr; 135 int err = 0; 136 137 tr = prog->aux->trampoline; 138 kind = bpf_attach_type_to_tramp(prog->expected_attach_type); 139 mutex_lock(&tr->mutex); 140 if (tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT] 141 >= BPF_MAX_TRAMP_PROGS) { 142 err = -E2BIG; 143 goto out; 144 } 145 if (!hlist_unhashed(&prog->aux->tramp_hlist)) { 146 /* prog already linked */ 147 err = -EBUSY; 148 goto out; 149 } 150 hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]); 151 tr->progs_cnt[kind]++; 152 err = bpf_trampoline_update(prog->aux->trampoline); 153 if (err) { 154 hlist_del(&prog->aux->tramp_hlist); 155 tr->progs_cnt[kind]--; 156 } 157 out: 158 mutex_unlock(&tr->mutex); 159 return err; 160 } 161 162 /* bpf_trampoline_unlink_prog() should never fail. */ 163 int bpf_trampoline_unlink_prog(struct bpf_prog *prog) 164 { 165 enum bpf_tramp_prog_type kind; 166 struct bpf_trampoline *tr; 167 int err; 168 169 tr = prog->aux->trampoline; 170 kind = bpf_attach_type_to_tramp(prog->expected_attach_type); 171 mutex_lock(&tr->mutex); 172 hlist_del(&prog->aux->tramp_hlist); 173 tr->progs_cnt[kind]--; 174 err = bpf_trampoline_update(prog->aux->trampoline); 175 mutex_unlock(&tr->mutex); 176 return err; 177 } 178 179 void bpf_trampoline_put(struct bpf_trampoline *tr) 180 { 181 if (!tr) 182 return; 183 mutex_lock(&trampoline_mutex); 184 if (!refcount_dec_and_test(&tr->refcnt)) 185 goto out; 186 WARN_ON_ONCE(mutex_is_locked(&tr->mutex)); 187 if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY]))) 188 goto out; 189 if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT]))) 190 goto out; 191 bpf_jit_free_exec(tr->image); 192 hlist_del(&tr->hlist); 193 kfree(tr); 194 out: 195 mutex_unlock(&trampoline_mutex); 196 } 197 198 /* The logic is similar to BPF_PROG_RUN, but with explicit rcu and preempt that 199 * are needed for trampoline. The macro is split into 200 * call _bpf_prog_enter 201 * call prog->bpf_func 202 * call __bpf_prog_exit 203 */ 204 u64 notrace __bpf_prog_enter(void) 205 { 206 u64 start = 0; 207 208 rcu_read_lock(); 209 preempt_disable(); 210 if (static_branch_unlikely(&bpf_stats_enabled_key)) 211 start = sched_clock(); 212 return start; 213 } 214 215 void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start) 216 { 217 struct bpf_prog_stats *stats; 218 219 if (static_branch_unlikely(&bpf_stats_enabled_key) && 220 /* static_key could be enabled in __bpf_prog_enter 221 * and disabled in __bpf_prog_exit. 222 * And vice versa. 223 * Hence check that 'start' is not zero. 224 */ 225 start) { 226 stats = this_cpu_ptr(prog->aux->stats); 227 u64_stats_update_begin(&stats->syncp); 228 stats->cnt++; 229 stats->nsecs += sched_clock() - start; 230 u64_stats_update_end(&stats->syncp); 231 } 232 preempt_enable(); 233 rcu_read_unlock(); 234 } 235 236 int __weak 237 arch_prepare_bpf_trampoline(void *image, struct btf_func_model *m, u32 flags, 238 struct bpf_prog **fentry_progs, int fentry_cnt, 239 struct bpf_prog **fexit_progs, int fexit_cnt, 240 void *orig_call) 241 { 242 return -ENOTSUPP; 243 } 244 245 static int __init init_trampolines(void) 246 { 247 int i; 248 249 for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++) 250 INIT_HLIST_HEAD(&trampoline_table[i]); 251 return 0; 252 } 253 late_initcall(init_trampolines); 254