kernel/bpf/trampoline.c - linux - Git at Google

 // 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>

 /* 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;
 }

 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;
 }

 /* 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 = unregister_fentry(tr, old_image);
 		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 = modify_fentry(tr, old_image, new_image);
 	else
 		/* first time registering */
 		err = register_fentry(tr, 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);
	// 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>

	/* 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;
	}

	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;
	}

	/* 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 = unregister_fentry(tr, old_image);
	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 = modify_fentry(tr, old_image, new_image);
	else
	/* first time registering */
	err = register_fentry(tr, 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);