diff options
Diffstat (limited to 'kernel/bpf/trampoline.c')
| -rw-r--r-- | kernel/bpf/trampoline.c | 253 |
1 files changed, 253 insertions, 0 deletions
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c new file mode 100644 index 000000000000..10ae59d65f13 --- /dev/null +++ b/kernel/bpf/trampoline.c @@ -0,0 +1,253 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright (c) 2019 Facebook */ +#include <linux/hash.h> +#include <linux/bpf.h> +#include <linux/filter.h> + +/* btf_vmlinux has ~22k attachable functions. 1k htab is enough. */ +#define TRAMPOLINE_HASH_BITS 10 +#define TRAMPOLINE_TABLE_SIZE (1 << TRAMPOLINE_HASH_BITS) + +static struct hlist_head trampoline_table[TRAMPOLINE_TABLE_SIZE]; + +/* serializes access to trampoline_table */ +static DEFINE_MUTEX(trampoline_mutex); + +struct bpf_trampoline *bpf_trampoline_lookup(u64 key) +{ + struct bpf_trampoline *tr; + struct hlist_head *head; + void *image; + int i; + + mutex_lock(&trampoline_mutex); + head = &trampoline_table[hash_64(key, TRAMPOLINE_HASH_BITS)]; + hlist_for_each_entry(tr, head, hlist) { + if (tr->key == key) { + refcount_inc(&tr->refcnt); + goto out; + } + } + tr = kzalloc(sizeof(*tr), GFP_KERNEL); + if (!tr) + goto out; + + /* is_root was checked earlier. No need for bpf_jit_charge_modmem() */ + image = bpf_jit_alloc_exec(PAGE_SIZE); + if (!image) { + kfree(tr); + tr = NULL; + goto out; + } + + tr->key = key; + INIT_HLIST_NODE(&tr->hlist); + hlist_add_head(&tr->hlist, head); + refcount_set(&tr->refcnt, 1); + mutex_init(&tr->mutex); + for (i = 0; i < BPF_TRAMP_MAX; i++) + INIT_HLIST_HEAD(&tr->progs_hlist[i]); + + set_vm_flush_reset_perms(image); + /* Keep image as writeable. The alternative is to keep flipping ro/rw + * everytime new program is attached or detached. + */ + set_memory_x((long)image, 1); + tr->image = image; +out: + mutex_unlock(&trampoline_mutex); + return tr; +} + +/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50 + * bytes on x86. Pick a number to fit into PAGE_SIZE / 2 + */ +#define BPF_MAX_TRAMP_PROGS 40 + +static int bpf_trampoline_update(struct bpf_trampoline *tr) +{ + void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2; + void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2; + struct bpf_prog *progs_to_run[BPF_MAX_TRAMP_PROGS]; + int fentry_cnt = tr->progs_cnt[BPF_TRAMP_FENTRY]; + int fexit_cnt = tr->progs_cnt[BPF_TRAMP_FEXIT]; + struct bpf_prog **progs, **fentry, **fexit; + u32 flags = BPF_TRAMP_F_RESTORE_REGS; + struct bpf_prog_aux *aux; + int err; + + if (fentry_cnt + fexit_cnt == 0) { + err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL_TO_NOP, + old_image, NULL); + tr->selector = 0; + goto out; + } + + /* populate fentry progs */ + fentry = progs = progs_to_run; + hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FENTRY], tramp_hlist) + *progs++ = aux->prog; + + /* populate fexit progs */ + fexit = progs; + hlist_for_each_entry(aux, &tr->progs_hlist[BPF_TRAMP_FEXIT], tramp_hlist) + *progs++ = aux->prog; + + if (fexit_cnt) + flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; + + err = arch_prepare_bpf_trampoline(new_image, &tr->func.model, flags, + fentry, fentry_cnt, + fexit, fexit_cnt, + tr->func.addr); + if (err) + goto out; + + if (tr->selector) + /* progs already running at this address */ + err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_CALL_TO_CALL, + old_image, new_image); + else + /* first time registering */ + err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_NOP_TO_CALL, + NULL, new_image); + if (err) + goto out; + tr->selector++; +out: + return err; +} + +static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(enum bpf_attach_type t) +{ + switch (t) { + case BPF_TRACE_FENTRY: + return BPF_TRAMP_FENTRY; + default: + return BPF_TRAMP_FEXIT; + } +} + +int bpf_trampoline_link_prog(struct bpf_prog *prog) +{ + enum bpf_tramp_prog_type kind; + struct bpf_trampoline *tr; + int err = 0; + + tr = prog->aux->trampoline; + kind = bpf_attach_type_to_tramp(prog->expected_attach_type); + mutex_lock(&tr->mutex); + if (tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT] + >= BPF_MAX_TRAMP_PROGS) { + err = -E2BIG; + goto out; + } + if (!hlist_unhashed(&prog->aux->tramp_hlist)) { + /* prog already linked */ + err = -EBUSY; + goto out; + } + hlist_add_head(&prog->aux->tramp_hlist, &tr->progs_hlist[kind]); + tr->progs_cnt[kind]++; + err = bpf_trampoline_update(prog->aux->trampoline); + if (err) { + hlist_del(&prog->aux->tramp_hlist); + tr->progs_cnt[kind]--; + } +out: + mutex_unlock(&tr->mutex); + return err; +} + +/* bpf_trampoline_unlink_prog() should never fail. */ +int bpf_trampoline_unlink_prog(struct bpf_prog *prog) +{ + enum bpf_tramp_prog_type kind; + struct bpf_trampoline *tr; + int err; + + tr = prog->aux->trampoline; + kind = bpf_attach_type_to_tramp(prog->expected_attach_type); + mutex_lock(&tr->mutex); + hlist_del(&prog->aux->tramp_hlist); + tr->progs_cnt[kind]--; + err = bpf_trampoline_update(prog->aux->trampoline); + mutex_unlock(&tr->mutex); + return err; +} + +void bpf_trampoline_put(struct bpf_trampoline *tr) +{ + if (!tr) + return; + mutex_lock(&trampoline_mutex); + if (!refcount_dec_and_test(&tr->refcnt)) + goto out; + WARN_ON_ONCE(mutex_is_locked(&tr->mutex)); + if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FENTRY]))) + goto out; + if (WARN_ON_ONCE(!hlist_empty(&tr->progs_hlist[BPF_TRAMP_FEXIT]))) + goto out; + bpf_jit_free_exec(tr->image); + hlist_del(&tr->hlist); + kfree(tr); +out: + mutex_unlock(&trampoline_mutex); +} + +/* The logic is similar to BPF_PROG_RUN, but with explicit rcu and preempt that + * are needed for trampoline. The macro is split into + * call _bpf_prog_enter + * call prog->bpf_func + * call __bpf_prog_exit + */ +u64 notrace __bpf_prog_enter(void) +{ + u64 start = 0; + + rcu_read_lock(); + preempt_disable(); + if (static_branch_unlikely(&bpf_stats_enabled_key)) + start = sched_clock(); + return start; +} + +void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start) +{ + struct bpf_prog_stats *stats; + + if (static_branch_unlikely(&bpf_stats_enabled_key) && + /* static_key could be enabled in __bpf_prog_enter + * and disabled in __bpf_prog_exit. + * And vice versa. + * Hence check that 'start' is not zero. + */ + start) { + stats = this_cpu_ptr(prog->aux->stats); + u64_stats_update_begin(&stats->syncp); + stats->cnt++; + stats->nsecs += sched_clock() - start; + u64_stats_update_end(&stats->syncp); + } + preempt_enable(); + rcu_read_unlock(); +} + +int __weak +arch_prepare_bpf_trampoline(void *image, struct btf_func_model *m, u32 flags, + struct bpf_prog **fentry_progs, int fentry_cnt, + struct bpf_prog **fexit_progs, int fexit_cnt, + void *orig_call) +{ + return -ENOTSUPP; +} + +static int __init init_trampolines(void) +{ + int i; + + for (i = 0; i < TRAMPOLINE_TABLE_SIZE; i++) + INIT_HLIST_HEAD(&trampoline_table[i]); + return 0; +} +late_initcall(init_trampolines); |