text: // 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>
  #include <linux/rcupdate_trace.h>
  #include <linux/rcupdate_wait.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);
  }
  
  static 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.
  	 * The same trampoline can hold both sleepable and non-sleepable progs.
  	 * synchronize_rcu_tasks_trace() is needed to make sure all sleepable
  	 * programs finish executing.
  	 * Wait for these two grace periods together.
  	 */
  	synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace);
  
  	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, struct bpf_trampoline *tr)
  {
  	enum bpf_tramp_prog_type kind;
  	int err = 0;
  	int cnt;
  
  	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(tr);
  	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, struct bpf_trampoline *tr)
  {
  	enum bpf_tramp_prog_type kind;
  	int err;
  
  	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(tr);
  out:
  	mutex_unlock(&tr->mutex);
  	return err;
  }
  
  struct bpf_trampoline *bpf_trampoline_get(u64 key,
  					  struct bpf_attach_target_info *tgt_info)
  {
  	struct bpf_trampoline *tr;
  
  	tr = bpf_trampoline_lookup(key);
  	if (!tr)
  		return NULL;
  
  	mutex_lock(&tr->mutex);
  	if (tr->func.addr)
  		goto out;
  
  	memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel));
  	tr->func.addr = (void *)tgt_info->tgt_addr;
  out:
  	mutex_unlock(&tr->mutex);
  	return tr;
  }
  
  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);
  	/* This code will be executed when all bpf progs (both sleepable and
  	 * non-sleepable) went through
  	 * bpf_prog_put()->call_rcu[_tasks_trace]()->bpf_prog_free_deferred().
  	 * Hence no need for another synchronize_rcu_tasks_trace() here,
  	 * but synchronize_rcu_tasks() is still needed, since trampoline
  	 * may not have had any sleepable programs and we need to wait
  	 * for tasks to get out of trampoline code 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();
  }
  
  void notrace __bpf_prog_enter_sleepable(void)
  {
  	rcu_read_lock_trace();
  	might_fault();
  }
  
  void notrace __bpf_prog_exit_sleepable(void)
  {
  	rcu_read_unlock_trace();
  }
  
  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);
  