kernel/trace/rethook.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0

 #define pr_fmt(fmt) "rethook: " fmt

 #include <linux/bug.h>
 #include <linux/kallsyms.h>
 #include <linux/kprobes.h>
 #include <linux/preempt.h>
 #include <linux/rethook.h>
 #include <linux/slab.h>
 #include <linux/sort.h>

 /* Return hook list (shadow stack by list) */

 /*
  * This function is called from delayed_put_task_struct() when a task is
  * dead and cleaned up to recycle any kretprobe instances associated with
  * this task. These left over instances represent probed functions that
  * have been called but will never return.
  */
 void rethook_flush_task(struct task_struct *tk)
 {
 	struct rethook_node *rhn;
 	struct llist_node *node;

 	node = __llist_del_all(&tk->rethooks);
 	while (node) {
 		rhn = container_of(node, struct rethook_node, llist);
 		node = node->next;
 		preempt_disable();
 		rethook_recycle(rhn);
 		preempt_enable();
 	}
 }

 static void rethook_free_rcu(struct rcu_head *head)
 {
 	struct rethook *rh = container_of(head, struct rethook, rcu);
 	struct rethook_node *rhn;
 	struct freelist_node *node;
 	int count = 1;

 	node = rh->pool.head;
 	while (node) {
 		rhn = container_of(node, struct rethook_node, freelist);
 		node = node->next;
 		kfree(rhn);
 		count++;
 	}

 	/* The rh->ref is the number of pooled node + 1 */
 	if (refcount_sub_and_test(count, &rh->ref))
 		kfree(rh);
 }

 /**
  * rethook_free() - Free struct rethook.
  * @rh: the struct rethook to be freed.
  *
  * Free the rethook. Before calling this function, user must ensure the
  * @rh::data is cleaned if needed (or, the handler can access it after
  * calling this function.) This function will set the @rh to be freed
  * after all rethook_node are freed (not soon). And the caller must
  * not touch @rh after calling this.
  */
 void rethook_free(struct rethook *rh)
 {
 	WRITE_ONCE(rh->handler, NULL);

 	call_rcu(&rh->rcu, rethook_free_rcu);
 }

 /**
  * rethook_alloc() - Allocate struct rethook.
  * @data: a data to pass the @handler when hooking the return.
  * @handler: the return hook callback function.
  *
  * Allocate and initialize a new rethook with @data and @handler.
  * Return NULL if memory allocation fails or @handler is NULL.
  * Note that @handler == NULL means this rethook is going to be freed.
  */
 struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
 {
 	struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);

 	if (!rh || !handler) {
 		kfree(rh);
 		return NULL;
 	}

 	rh->data = data;
 	rh->handler = handler;
 	rh->pool.head = NULL;
 	refcount_set(&rh->ref, 1);

 	return rh;
 }

 /**
  * rethook_add_node() - Add a new node to the rethook.
  * @rh: the struct rethook.
  * @node: the struct rethook_node to be added.
  *
  * Add @node to @rh. User must allocate @node (as a part of user's
  * data structure.) The @node fields are initialized in this function.
  */
 void rethook_add_node(struct rethook *rh, struct rethook_node *node)
 {
 	node->rethook = rh;
 	freelist_add(&node->freelist, &rh->pool);
 	refcount_inc(&rh->ref);
 }

 static void free_rethook_node_rcu(struct rcu_head *head)
 {
 	struct rethook_node *node = container_of(head, struct rethook_node, rcu);

 	if (refcount_dec_and_test(&node->rethook->ref))
 		kfree(node->rethook);
 	kfree(node);
 }

 /**
  * rethook_recycle() - return the node to rethook.
  * @node: The struct rethook_node to be returned.
  *
  * Return back the @node to @node::rethook. If the @node::rethook is already
  * marked as freed, this will free the @node.
  */
 void rethook_recycle(struct rethook_node *node)
 {
 	lockdep_assert_preemption_disabled();

 	if (likely(READ_ONCE(node->rethook->handler)))
 		freelist_add(&node->freelist, &node->rethook->pool);
 	else
 		call_rcu(&node->rcu, free_rethook_node_rcu);
 }
 NOKPROBE_SYMBOL(rethook_recycle);

 /**
  * rethook_try_get() - get an unused rethook node.
  * @rh: The struct rethook which pools the nodes.
  *
  * Get an unused rethook node from @rh. If the node pool is empty, this
  * will return NULL. Caller must disable preemption.
  */
 struct rethook_node *rethook_try_get(struct rethook *rh)
 {
 	rethook_handler_t handler = READ_ONCE(rh->handler);
 	struct freelist_node *fn;

 	lockdep_assert_preemption_disabled();

 	/* Check whether @rh is going to be freed. */
 	if (unlikely(!handler))
 		return NULL;

 	/*
 	 * This expects the caller will set up a rethook on a function entry.
 	 * When the function returns, the rethook will eventually be reclaimed
 	 * or released in the rethook_recycle() with call_rcu().
 	 * This means the caller must be run in the RCU-availabe context.
 	 */
 	if (unlikely(!rcu_is_watching()))
 		return NULL;

 	fn = freelist_try_get(&rh->pool);
 	if (!fn)
 		return NULL;

 	return container_of(fn, struct rethook_node, freelist);
 }
 NOKPROBE_SYMBOL(rethook_try_get);

 /**
  * rethook_hook() - Hook the current function return.
  * @node: The struct rethook node to hook the function return.
  * @regs: The struct pt_regs for the function entry.
  * @mcount: True if this is called from mcount(ftrace) context.
  *
  * Hook the current running function return. This must be called when the
  * function entry (or at least @regs must be the registers of the function
  * entry.) @mcount is used for identifying the context. If this is called
  * from ftrace (mcount) callback, @mcount must be set true. If this is called
  * from the real function entry (e.g. kprobes) @mcount must be set false.
  * This is because the way to hook the function return depends on the context.
  */
 void rethook_hook(struct rethook_node *node, struct pt_regs *regs, bool mcount)
 {
 	arch_rethook_prepare(node, regs, mcount);
 	__llist_add(&node->llist, &current->rethooks);
 }
 NOKPROBE_SYMBOL(rethook_hook);

 /* This assumes the 'tsk' is the current task or is not running. */
 static unsigned long __rethook_find_ret_addr(struct task_struct *tsk,
 					     struct llist_node **cur)
 {
 	struct rethook_node *rh = NULL;
 	struct llist_node *node = *cur;

 	if (!node)
 		node = tsk->rethooks.first;
 	else
 		node = node->next;

 	while (node) {
 		rh = container_of(node, struct rethook_node, llist);
 		if (rh->ret_addr != (unsigned long)arch_rethook_trampoline) {
 			*cur = node;
 			return rh->ret_addr;
 		}
 		node = node->next;
 	}
 	return 0;
 }
 NOKPROBE_SYMBOL(__rethook_find_ret_addr);

 /**
  * rethook_find_ret_addr -- Find correct return address modified by rethook
  * @tsk: Target task
  * @frame: A frame pointer
  * @cur: a storage of the loop cursor llist_node pointer for next call
  *
  * Find the correct return address modified by a rethook on @tsk in unsigned
  * long type.
  * The @tsk must be 'current' or a task which is not running. @frame is a hint
  * to get the currect return address - which is compared with the
  * rethook::frame field. The @cur is a loop cursor for searching the
  * kretprobe return addresses on the @tsk. The '*@cur' should be NULL at the
  * first call, but '@cur' itself must NOT NULL.
  *
  * Returns found address value or zero if not found.
  */
 unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame,
 				    struct llist_node **cur)
 {
 	struct rethook_node *rhn = NULL;
 	unsigned long ret;

 	if (WARN_ON_ONCE(!cur))
 		return 0;

 	if (WARN_ON_ONCE(tsk != current && task_is_running(tsk)))
 		return 0;

 	do {
 		ret = __rethook_find_ret_addr(tsk, cur);
 		if (!ret)
 			break;
 		rhn = container_of(*cur, struct rethook_node, llist);
 	} while (rhn->frame != frame);

 	return ret;
 }
 NOKPROBE_SYMBOL(rethook_find_ret_addr);

 void __weak arch_rethook_fixup_return(struct pt_regs *regs,
 				      unsigned long correct_ret_addr)
 {
 	/*
 	 * Do nothing by default. If the architecture which uses a
 	 * frame pointer to record real return address on the stack,
 	 * it should fill this function to fixup the return address
 	 * so that stacktrace works from the rethook handler.
 	 */
 }

 /* This function will be called from each arch-defined trampoline. */
 unsigned long rethook_trampoline_handler(struct pt_regs *regs,
 					 unsigned long frame)
 {
 	struct llist_node *first, *node = NULL;
 	unsigned long correct_ret_addr;
 	rethook_handler_t handler;
 	struct rethook_node *rhn;

 	correct_ret_addr = __rethook_find_ret_addr(current, &node);
 	if (!correct_ret_addr) {
 		pr_err("rethook: Return address not found! Maybe there is a bug in the kernel\n");
 		BUG_ON(1);
 	}

 	instruction_pointer_set(regs, correct_ret_addr);

 	/*
 	 * These loops must be protected from rethook_free_rcu() because those
 	 * are accessing 'rhn->rethook'.
 	 */
 	preempt_disable();

 	/*
 	 * Run the handler on the shadow stack. Do not unlink the list here because
 	 * stackdump inside the handlers needs to decode it.
 	 */
 	first = current->rethooks.first;
 	while (first) {
 		rhn = container_of(first, struct rethook_node, llist);
 		if (WARN_ON_ONCE(rhn->frame != frame))
 			break;
 		handler = READ_ONCE(rhn->rethook->handler);
 		if (handler)
 			handler(rhn, rhn->rethook->data, regs);

 		if (first == node)
 			break;
 		first = first->next;
 	}

 	/* Fixup registers for returning to correct address. */
 	arch_rethook_fixup_return(regs, correct_ret_addr);

 	/* Unlink used shadow stack */
 	first = current->rethooks.first;
 	current->rethooks.first = node->next;
 	node->next = NULL;

 	while (first) {
 		rhn = container_of(first, struct rethook_node, llist);
 		first = first->next;
 		rethook_recycle(rhn);
 	}
 	preempt_enable();

 	return correct_ret_addr;
 }
 NOKPROBE_SYMBOL(rethook_trampoline_handler);
	// SPDX-License-Identifier: GPL-2.0

	#define pr_fmt(fmt) "rethook: " fmt

	#include <linux/bug.h>
	#include <linux/kallsyms.h>
	#include <linux/kprobes.h>
	#include <linux/preempt.h>
	#include <linux/rethook.h>
	#include <linux/slab.h>
	#include <linux/sort.h>

	/* Return hook list (shadow stack by list) */

	/*
	* This function is called from delayed_put_task_struct() when a task is
	* dead and cleaned up to recycle any kretprobe instances associated with
	* this task. These left over instances represent probed functions that
	* have been called but will never return.
	*/
	void rethook_flush_task(struct task_struct *tk)
	{
	struct rethook_node *rhn;
	struct llist_node *node;

	node = __llist_del_all(&tk->rethooks);
	while (node) {
	rhn = container_of(node, struct rethook_node, llist);
	node = node->next;
	preempt_disable();
	rethook_recycle(rhn);
	preempt_enable();
	}
	}

	static void rethook_free_rcu(struct rcu_head *head)
	{
	struct rethook *rh = container_of(head, struct rethook, rcu);
	struct rethook_node *rhn;
	struct freelist_node *node;
	int count = 1;

	node = rh->pool.head;
	while (node) {
	rhn = container_of(node, struct rethook_node, freelist);
	node = node->next;
	kfree(rhn);
	count++;
	}

	/* The rh->ref is the number of pooled node + 1 */
	if (refcount_sub_and_test(count, &rh->ref))
	kfree(rh);
	}

	/**
	* rethook_free() - Free struct rethook.
	* @rh: the struct rethook to be freed.
	*
	* Free the rethook. Before calling this function, user must ensure the
	* @rh::data is cleaned if needed (or, the handler can access it after
	* calling this function.) This function will set the @rh to be freed
	* after all rethook_node are freed (not soon). And the caller must
	* not touch @rh after calling this.
	*/
	void rethook_free(struct rethook *rh)
	{
	WRITE_ONCE(rh->handler, NULL);

	call_rcu(&rh->rcu, rethook_free_rcu);
	}

	/**
	* rethook_alloc() - Allocate struct rethook.
	* @data: a data to pass the @handler when hooking the return.
	* @handler: the return hook callback function.
	*
	* Allocate and initialize a new rethook with @data and @handler.
	* Return NULL if memory allocation fails or @handler is NULL.
	* Note that @handler == NULL means this rethook is going to be freed.
	*/
	struct rethook rethook_alloc(void data, rethook_handler_t handler)
	{
	struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);

	if (!rh \|\| !handler) {
	kfree(rh);
	return NULL;
	}

	rh->data = data;
	rh->handler = handler;
	rh->pool.head = NULL;
	refcount_set(&rh->ref, 1);

	return rh;
	}

	/**
	* rethook_add_node() - Add a new node to the rethook.
	* @rh: the struct rethook.
	* @node: the struct rethook_node to be added.
	*
	* Add @node to @rh. User must allocate @node (as a part of user's
	* data structure.) The @node fields are initialized in this function.
	*/
	void rethook_add_node(struct rethook rh, struct rethook_node node)
	{
	node->rethook = rh;
	freelist_add(&node->freelist, &rh->pool);
	refcount_inc(&rh->ref);
	}

	static void free_rethook_node_rcu(struct rcu_head *head)
	{
	struct rethook_node *node = container_of(head, struct rethook_node, rcu);

	if (refcount_dec_and_test(&node->rethook->ref))
	kfree(node->rethook);
	kfree(node);
	}

	/**
	* rethook_recycle() - return the node to rethook.
	* @node: The struct rethook_node to be returned.
	*
	* Return back the @node to @node::rethook. If the @node::rethook is already
	* marked as freed, this will free the @node.
	*/
	void rethook_recycle(struct rethook_node *node)
	{
	lockdep_assert_preemption_disabled();

	if (likely(READ_ONCE(node->rethook->handler)))
	freelist_add(&node->freelist, &node->rethook->pool);
	else
	call_rcu(&node->rcu, free_rethook_node_rcu);
	}
	NOKPROBE_SYMBOL(rethook_recycle);

	/**
	* rethook_try_get() - get an unused rethook node.
	* @rh: The struct rethook which pools the nodes.
	*
	* Get an unused rethook node from @rh. If the node pool is empty, this
	* will return NULL. Caller must disable preemption.
	*/
	struct rethook_node rethook_try_get(struct rethook rh)
	{
	rethook_handler_t handler = READ_ONCE(rh->handler);
	struct freelist_node *fn;

	lockdep_assert_preemption_disabled();

	/* Check whether @rh is going to be freed. */
	if (unlikely(!handler))
	return NULL;

	/*
	* This expects the caller will set up a rethook on a function entry.
	* When the function returns, the rethook will eventually be reclaimed
	* or released in the rethook_recycle() with call_rcu().
	* This means the caller must be run in the RCU-availabe context.
	*/
	if (unlikely(!rcu_is_watching()))
	return NULL;

	fn = freelist_try_get(&rh->pool);
	if (!fn)
	return NULL;

	return container_of(fn, struct rethook_node, freelist);
	}
	NOKPROBE_SYMBOL(rethook_try_get);

	/**
	* rethook_hook() - Hook the current function return.
	* @node: The struct rethook node to hook the function return.
	* @regs: The struct pt_regs for the function entry.
	* @mcount: True if this is called from mcount(ftrace) context.
	*
	* Hook the current running function return. This must be called when the
	* function entry (or at least @regs must be the registers of the function
	* entry.) @mcount is used for identifying the context. If this is called
	* from ftrace (mcount) callback, @mcount must be set true. If this is called
	* from the real function entry (e.g. kprobes) @mcount must be set false.
	* This is because the way to hook the function return depends on the context.
	*/
	void rethook_hook(struct rethook_node node, struct pt_regs regs, bool mcount)
	{
	arch_rethook_prepare(node, regs, mcount);
	__llist_add(&node->llist, &current->rethooks);
	}
	NOKPROBE_SYMBOL(rethook_hook);

	/* This assumes the 'tsk' is the current task or is not running. */
	static unsigned long __rethook_find_ret_addr(struct task_struct *tsk,
	struct llist_node **cur)
	{
	struct rethook_node *rh = NULL;
	struct llist_node node = cur;

	if (!node)
	node = tsk->rethooks.first;
	else
	node = node->next;

	while (node) {
	rh = container_of(node, struct rethook_node, llist);
	if (rh->ret_addr != (unsigned long)arch_rethook_trampoline) {
	*cur = node;
	return rh->ret_addr;
	}
	node = node->next;
	}
	return 0;
	}
	NOKPROBE_SYMBOL(__rethook_find_ret_addr);

	/**
	* rethook_find_ret_addr -- Find correct return address modified by rethook
	* @tsk: Target task
	* @frame: A frame pointer
	* @cur: a storage of the loop cursor llist_node pointer for next call
	*
	* Find the correct return address modified by a rethook on @tsk in unsigned
	* long type.
	* The @tsk must be 'current' or a task which is not running. @frame is a hint
	* to get the currect return address - which is compared with the
	* rethook::frame field. The @cur is a loop cursor for searching the
	* kretprobe return addresses on the @tsk. The '*@cur' should be NULL at the
	* first call, but '@cur' itself must NOT NULL.
	*
	* Returns found address value or zero if not found.
	*/
	unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame,
	struct llist_node **cur)
	{
	struct rethook_node *rhn = NULL;
	unsigned long ret;

	if (WARN_ON_ONCE(!cur))
	return 0;

	if (WARN_ON_ONCE(tsk != current && task_is_running(tsk)))
	return 0;

	do {
	ret = __rethook_find_ret_addr(tsk, cur);
	if (!ret)
	break;
	rhn = container_of(*cur, struct rethook_node, llist);
	} while (rhn->frame != frame);

	return ret;
	}
	NOKPROBE_SYMBOL(rethook_find_ret_addr);

	void __weak arch_rethook_fixup_return(struct pt_regs *regs,
	unsigned long correct_ret_addr)
	{
	/*
	* Do nothing by default. If the architecture which uses a
	* frame pointer to record real return address on the stack,
	* it should fill this function to fixup the return address
	* so that stacktrace works from the rethook handler.
	*/
	}

	/* This function will be called from each arch-defined trampoline. */
	unsigned long rethook_trampoline_handler(struct pt_regs *regs,
	unsigned long frame)
	{
	struct llist_node first, node = NULL;
	unsigned long correct_ret_addr;
	rethook_handler_t handler;
	struct rethook_node *rhn;

	correct_ret_addr = __rethook_find_ret_addr(current, &node);
	if (!correct_ret_addr) {
	pr_err("rethook: Return address not found! Maybe there is a bug in the kernel\n");
	BUG_ON(1);
	}

	instruction_pointer_set(regs, correct_ret_addr);

	/*
	* These loops must be protected from rethook_free_rcu() because those
	* are accessing 'rhn->rethook'.
	*/
	preempt_disable();

	/*
	* Run the handler on the shadow stack. Do not unlink the list here because
	* stackdump inside the handlers needs to decode it.
	*/
	first = current->rethooks.first;
	while (first) {
	rhn = container_of(first, struct rethook_node, llist);
	if (WARN_ON_ONCE(rhn->frame != frame))
	break;
	handler = READ_ONCE(rhn->rethook->handler);
	if (handler)
	handler(rhn, rhn->rethook->data, regs);

	if (first == node)
	break;
	first = first->next;
	}

	/* Fixup registers for returning to correct address. */
	arch_rethook_fixup_return(regs, correct_ret_addr);

	/* Unlink used shadow stack */
	first = current->rethooks.first;
	current->rethooks.first = node->next;
	node->next = NULL;

	while (first) {
	rhn = container_of(first, struct rethook_node, llist);
	first = first->next;
	rethook_recycle(rhn);
	}
	preempt_enable();

	return correct_ret_addr;
	}
	NOKPROBE_SYMBOL(rethook_trampoline_handler);