// SPDX-License-Identifier: GPL-2.0-only /* Copyright (c) 2019 Facebook */ #include <linux/hash.h> #include <linux/bpf.h> #include <linux/filter.h> #include <linux/ftrace.h> #include <linux/rbtree_latch.h> #include <linux/perf_event.h> #include <linux/btf.h> /* dummy _ops. The verifier will operate on target program's ops. */ const struct bpf_verifier_ops bpf_extension_verifier_ops = { }; const struct bpf_prog_ops bpf_extension_prog_ops = { }; /* 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); void *bpf_jit_alloc_exec_page(void) { void *image; image = bpf_jit_alloc_exec(PAGE_SIZE); if (!image) return NULL; 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); return image; } void bpf_image_ksym_add(void *data, struct bpf_ksym *ksym) { ksym->start = (unsigned long) data; ksym->end = ksym->start + PAGE_SIZE; bpf_ksym_add(ksym); perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start, PAGE_SIZE, false, ksym->name); } void bpf_image_ksym_del(struct bpf_ksym *ksym) { bpf_ksym_del(ksym); perf_event_ksymbol(PERF_RECORD_KSYMBOL_TYPE_BPF, ksym->start, PAGE_SIZE, true, ksym->name); } static void bpf_trampoline_ksym_add(struct bpf_trampoline *tr) { struct bpf_ksym *ksym = &tr->ksym; snprintf(ksym->name, KSYM_NAME_LEN, "bpf_trampoline_%llu", tr->key); bpf_image_ksym_add(tr->image, ksym); } 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(); 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]); tr->image = image; INIT_LIST_HEAD_RCU(&tr->ksym.lnode); bpf_trampoline_ksym_add(tr); out: mutex_unlock(&trampoline_mutex); return tr; } static int is_ftrace_location(void *ip) { long addr; addr = ftrace_location((long)ip); if (!addr) return 0; if (WARN_ON_ONCE(addr != (long)ip)) return -EFAULT; return 1; } static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr) { void *ip = tr->func.addr; int ret; if (tr->func.ftrace_managed) ret = unregister_ftrace_direct((long)ip, (long)old_addr); else ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL); return ret; } static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr) { void *ip = tr->func.addr; int ret; if (tr->func.ftrace_managed) ret = modify_ftrace_direct((long)ip, (long)old_addr, (long)new_addr); else ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, new_addr); return ret; } /* first time registering */ static int register_fentry(struct bpf_trampoline *tr, void *new_addr) { void *ip = tr->func.addr; int ret; ret = is_ftrace_location(ip); if (ret < 0) return ret; tr->func.ftrace_managed = ret; if (tr->func.ftrace_managed) ret = register_ftrace_direct((long)ip, (long)new_addr); else ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr); return ret; } static struct bpf_tramp_progs * bpf_trampoline_get_progs(const struct bpf_trampoline *tr, int *total) { const struct bpf_prog_aux *aux; struct bpf_tramp_progs *tprogs; struct bpf_prog **progs; int kind; *total = 0; tprogs = kcalloc(BPF_TRAMP_MAX, sizeof(*tprogs), GFP_KERNEL); if (!tprogs) return ERR_PTR(-ENOMEM); for (kind = 0; kind < BPF_TRAMP_MAX; kind++) { tprogs[kind].nr_progs = tr->progs_cnt[kind]; *total += tr->progs_cnt[kind]; progs = tprogs[kind].progs; hlist_for_each_entry(aux, &tr->progs_hlist[kind], tramp_hlist) *progs++ = aux->prog; } return tprogs; } 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_tramp_progs *tprogs; u32 flags = BPF_TRAMP_F_RESTORE_REGS; int err, total; tprogs = bpf_trampoline_get_progs(tr, &total); if (IS_ERR(tprogs)) return PTR_ERR(tprogs); if (total == 0) { err = unregister_fentry(tr, old_image); tr->selector = 0; goto out; } if (tprogs[BPF_TRAMP_FEXIT].nr_progs || tprogs[BPF_TRAMP_MODIFY_RETURN].nr_progs) flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME; /* Though the second half of trampoline page is unused a task could be * preempted in the middle of the first half of trampoline and two * updates to trampoline would change the code from underneath the * preempted task. Hence wait for tasks to voluntarily schedule or go * to userspace. */ synchronize_rcu_tasks(); err = arch_prepare_bpf_trampoline(new_image, new_image + PAGE_SIZE / 2, &tr->func.model, flags, tprogs, tr->func.addr); if (err < 0) goto out; if (tr->selector) /* progs already running at this address */ err = modify_fentry(tr, old_image, new_image); else /* first time registering */ err = register_fentry(tr, new_image); if (err) goto out; tr->selector++; out: kfree(tprogs); return err; } static enum bpf_tramp_prog_type bpf_attach_type_to_tramp(struct bpf_prog *prog) { switch (prog->expected_attach_type) { case BPF_TRACE_FENTRY: return BPF_TRAMP_FENTRY; case BPF_MODIFY_RETURN: return BPF_TRAMP_MODIFY_RETURN; case BPF_TRACE_FEXIT: return BPF_TRAMP_FEXIT; case BPF_LSM_MAC: if (!prog->aux->attach_func_proto->type) /* The function returns void, we cannot modify its * return value. */ return BPF_TRAMP_FEXIT; else return BPF_TRAMP_MODIFY_RETURN; default: return BPF_TRAMP_REPLACE; } } int bpf_trampoline_link_prog(struct bpf_prog *prog) { enum bpf_tramp_prog_type kind; struct bpf_trampoline *tr; int err = 0; int cnt; tr = prog->aux->trampoline; kind = bpf_attach_type_to_tramp(prog); mutex_lock(&tr->mutex); if (tr->extension_prog) { /* cannot attach fentry/fexit if extension prog is attached. * cannot overwrite extension prog either. */ err = -EBUSY; goto out; } cnt = tr->progs_cnt[BPF_TRAMP_FENTRY] + tr->progs_cnt[BPF_TRAMP_FEXIT]; if (kind == BPF_TRAMP_REPLACE) { /* Cannot attach extension if fentry/fexit are in use. */ if (cnt) { err = -EBUSY; goto out; } tr->extension_prog = prog; err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, NULL, prog->bpf_func); goto out; } if (cnt >= 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); mutex_lock(&tr->mutex); if (kind == BPF_TRAMP_REPLACE) { WARN_ON_ONCE(!tr->extension_prog); err = bpf_arch_text_poke(tr->func.addr, BPF_MOD_JUMP, tr->extension_prog->bpf_func, NULL); tr->extension_prog = NULL; goto out; } hlist_del(&prog->aux->tramp_hlist); tr->progs_cnt[kind]--; err = bpf_trampoline_update(prog->aux->trampoline); out: 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_image_ksym_del(&tr->ksym); /* wait for tasks to get out of trampoline before freeing it */ synchronize_rcu_tasks(); 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 an explicit * rcu_read_lock() and migrate_disable() which are required * for the trampoline. The macro is split into * call _bpf_prog_enter * call prog->bpf_func * call __bpf_prog_exit */ u64 notrace __bpf_prog_enter(void) __acquires(RCU) { u64 start = 0; rcu_read_lock(); migrate_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) __releases(RCU) { 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); } migrate_enable(); rcu_read_unlock(); } int __weak arch_prepare_bpf_trampoline(void *image, void *image_end, const struct btf_func_model *m, u32 flags, struct bpf_tramp_progs *tprogs, 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);