1 | // SPDX-License-Identifier: GPL-2.0 |
2 | |
3 | #define pr_fmt(fmt) "rethook: " fmt |
4 | |
5 | #include <linux/bug.h> |
6 | #include <linux/kallsyms.h> |
7 | #include <linux/kprobes.h> |
8 | #include <linux/preempt.h> |
9 | #include <linux/rethook.h> |
10 | #include <linux/slab.h> |
11 | |
12 | /* Return hook list (shadow stack by list) */ |
13 | |
14 | /* |
15 | * This function is called from delayed_put_task_struct() when a task is |
16 | * dead and cleaned up to recycle any kretprobe instances associated with |
17 | * this task. These left over instances represent probed functions that |
18 | * have been called but will never return. |
19 | */ |
20 | void rethook_flush_task(struct task_struct *tk) |
21 | { |
22 | struct rethook_node *rhn; |
23 | struct llist_node *node; |
24 | |
25 | node = __llist_del_all(head: &tk->rethooks); |
26 | while (node) { |
27 | rhn = container_of(node, struct rethook_node, llist); |
28 | node = node->next; |
29 | preempt_disable(); |
30 | rethook_recycle(node: rhn); |
31 | preempt_enable(); |
32 | } |
33 | } |
34 | |
35 | static void rethook_free_rcu(struct rcu_head *head) |
36 | { |
37 | struct rethook *rh = container_of(head, struct rethook, rcu); |
38 | objpool_fini(pool: &rh->pool); |
39 | } |
40 | |
41 | /** |
42 | * rethook_stop() - Stop using a rethook. |
43 | * @rh: the struct rethook to stop. |
44 | * |
45 | * Stop using a rethook to prepare for freeing it. If you want to wait for |
46 | * all running rethook handler before calling rethook_free(), you need to |
47 | * call this first and wait RCU, and call rethook_free(). |
48 | */ |
49 | void rethook_stop(struct rethook *rh) |
50 | { |
51 | rcu_assign_pointer(rh->handler, NULL); |
52 | } |
53 | |
54 | /** |
55 | * rethook_free() - Free struct rethook. |
56 | * @rh: the struct rethook to be freed. |
57 | * |
58 | * Free the rethook. Before calling this function, user must ensure the |
59 | * @rh::data is cleaned if needed (or, the handler can access it after |
60 | * calling this function.) This function will set the @rh to be freed |
61 | * after all rethook_node are freed (not soon). And the caller must |
62 | * not touch @rh after calling this. |
63 | */ |
64 | void rethook_free(struct rethook *rh) |
65 | { |
66 | rethook_stop(rh); |
67 | |
68 | call_rcu(head: &rh->rcu, func: rethook_free_rcu); |
69 | } |
70 | |
71 | static int rethook_init_node(void *nod, void *context) |
72 | { |
73 | struct rethook_node *node = nod; |
74 | |
75 | node->rethook = context; |
76 | return 0; |
77 | } |
78 | |
79 | static int rethook_fini_pool(struct objpool_head *head, void *context) |
80 | { |
81 | kfree(objp: context); |
82 | return 0; |
83 | } |
84 | |
85 | static inline rethook_handler_t rethook_get_handler(struct rethook *rh) |
86 | { |
87 | return (rethook_handler_t)rcu_dereference_check(rh->handler, |
88 | rcu_read_lock_any_held()); |
89 | } |
90 | |
91 | /** |
92 | * rethook_alloc() - Allocate struct rethook. |
93 | * @data: a data to pass the @handler when hooking the return. |
94 | * @handler: the return hook callback function, must NOT be NULL |
95 | * @size: node size: rethook node and additional data |
96 | * @num: number of rethook nodes to be preallocated |
97 | * |
98 | * Allocate and initialize a new rethook with @data and @handler. |
99 | * Return pointer of new rethook, or error codes for failures. |
100 | * |
101 | * Note that @handler == NULL means this rethook is going to be freed. |
102 | */ |
103 | struct rethook *rethook_alloc(void *data, rethook_handler_t handler, |
104 | int size, int num) |
105 | { |
106 | struct rethook *rh; |
107 | |
108 | if (!handler || num <= 0 || size < sizeof(struct rethook_node)) |
109 | return ERR_PTR(error: -EINVAL); |
110 | |
111 | rh = kzalloc(size: sizeof(struct rethook), GFP_KERNEL); |
112 | if (!rh) |
113 | return ERR_PTR(error: -ENOMEM); |
114 | |
115 | rh->data = data; |
116 | rcu_assign_pointer(rh->handler, handler); |
117 | |
118 | /* initialize the objpool for rethook nodes */ |
119 | if (objpool_init(pool: &rh->pool, nr_objs: num, object_size: size, GFP_KERNEL, context: rh, |
120 | objinit: rethook_init_node, release: rethook_fini_pool)) { |
121 | kfree(objp: rh); |
122 | return ERR_PTR(error: -ENOMEM); |
123 | } |
124 | return rh; |
125 | } |
126 | |
127 | static void free_rethook_node_rcu(struct rcu_head *head) |
128 | { |
129 | struct rethook_node *node = container_of(head, struct rethook_node, rcu); |
130 | struct rethook *rh = node->rethook; |
131 | |
132 | objpool_drop(obj: node, pool: &rh->pool); |
133 | } |
134 | |
135 | /** |
136 | * rethook_recycle() - return the node to rethook. |
137 | * @node: The struct rethook_node to be returned. |
138 | * |
139 | * Return back the @node to @node::rethook. If the @node::rethook is already |
140 | * marked as freed, this will free the @node. |
141 | */ |
142 | void rethook_recycle(struct rethook_node *node) |
143 | { |
144 | rethook_handler_t handler; |
145 | |
146 | handler = rethook_get_handler(rh: node->rethook); |
147 | if (likely(handler)) |
148 | objpool_push(obj: node, pool: &node->rethook->pool); |
149 | else |
150 | call_rcu(head: &node->rcu, func: free_rethook_node_rcu); |
151 | } |
152 | NOKPROBE_SYMBOL(rethook_recycle); |
153 | |
154 | /** |
155 | * rethook_try_get() - get an unused rethook node. |
156 | * @rh: The struct rethook which pools the nodes. |
157 | * |
158 | * Get an unused rethook node from @rh. If the node pool is empty, this |
159 | * will return NULL. Caller must disable preemption. |
160 | */ |
161 | struct rethook_node *rethook_try_get(struct rethook *rh) |
162 | { |
163 | rethook_handler_t handler = rethook_get_handler(rh); |
164 | |
165 | /* Check whether @rh is going to be freed. */ |
166 | if (unlikely(!handler)) |
167 | return NULL; |
168 | |
169 | /* |
170 | * This expects the caller will set up a rethook on a function entry. |
171 | * When the function returns, the rethook will eventually be reclaimed |
172 | * or released in the rethook_recycle() with call_rcu(). |
173 | * This means the caller must be run in the RCU-availabe context. |
174 | */ |
175 | if (unlikely(!rcu_is_watching())) |
176 | return NULL; |
177 | |
178 | return (struct rethook_node *)objpool_pop(pool: &rh->pool); |
179 | } |
180 | NOKPROBE_SYMBOL(rethook_try_get); |
181 | |
182 | /** |
183 | * rethook_hook() - Hook the current function return. |
184 | * @node: The struct rethook node to hook the function return. |
185 | * @regs: The struct pt_regs for the function entry. |
186 | * @mcount: True if this is called from mcount(ftrace) context. |
187 | * |
188 | * Hook the current running function return. This must be called when the |
189 | * function entry (or at least @regs must be the registers of the function |
190 | * entry.) @mcount is used for identifying the context. If this is called |
191 | * from ftrace (mcount) callback, @mcount must be set true. If this is called |
192 | * from the real function entry (e.g. kprobes) @mcount must be set false. |
193 | * This is because the way to hook the function return depends on the context. |
194 | */ |
195 | void rethook_hook(struct rethook_node *node, struct pt_regs *regs, bool mcount) |
196 | { |
197 | arch_rethook_prepare(node, regs, mcount); |
198 | __llist_add(new: &node->llist, head: ¤t->rethooks); |
199 | } |
200 | NOKPROBE_SYMBOL(rethook_hook); |
201 | |
202 | /* This assumes the 'tsk' is the current task or is not running. */ |
203 | static unsigned long __rethook_find_ret_addr(struct task_struct *tsk, |
204 | struct llist_node **cur) |
205 | { |
206 | struct rethook_node *rh = NULL; |
207 | struct llist_node *node = *cur; |
208 | |
209 | if (!node) |
210 | node = tsk->rethooks.first; |
211 | else |
212 | node = node->next; |
213 | |
214 | while (node) { |
215 | rh = container_of(node, struct rethook_node, llist); |
216 | if (rh->ret_addr != (unsigned long)arch_rethook_trampoline) { |
217 | *cur = node; |
218 | return rh->ret_addr; |
219 | } |
220 | node = node->next; |
221 | } |
222 | return 0; |
223 | } |
224 | NOKPROBE_SYMBOL(__rethook_find_ret_addr); |
225 | |
226 | /** |
227 | * rethook_find_ret_addr -- Find correct return address modified by rethook |
228 | * @tsk: Target task |
229 | * @frame: A frame pointer |
230 | * @cur: a storage of the loop cursor llist_node pointer for next call |
231 | * |
232 | * Find the correct return address modified by a rethook on @tsk in unsigned |
233 | * long type. |
234 | * The @tsk must be 'current' or a task which is not running. @frame is a hint |
235 | * to get the currect return address - which is compared with the |
236 | * rethook::frame field. The @cur is a loop cursor for searching the |
237 | * kretprobe return addresses on the @tsk. The '*@cur' should be NULL at the |
238 | * first call, but '@cur' itself must NOT NULL. |
239 | * |
240 | * Returns found address value or zero if not found. |
241 | */ |
242 | unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame, |
243 | struct llist_node **cur) |
244 | { |
245 | struct rethook_node *rhn = NULL; |
246 | unsigned long ret; |
247 | |
248 | if (WARN_ON_ONCE(!cur)) |
249 | return 0; |
250 | |
251 | if (WARN_ON_ONCE(tsk != current && task_is_running(tsk))) |
252 | return 0; |
253 | |
254 | do { |
255 | ret = __rethook_find_ret_addr(tsk, cur); |
256 | if (!ret) |
257 | break; |
258 | rhn = container_of(*cur, struct rethook_node, llist); |
259 | } while (rhn->frame != frame); |
260 | |
261 | return ret; |
262 | } |
263 | NOKPROBE_SYMBOL(rethook_find_ret_addr); |
264 | |
265 | void __weak arch_rethook_fixup_return(struct pt_regs *regs, |
266 | unsigned long correct_ret_addr) |
267 | { |
268 | /* |
269 | * Do nothing by default. If the architecture which uses a |
270 | * frame pointer to record real return address on the stack, |
271 | * it should fill this function to fixup the return address |
272 | * so that stacktrace works from the rethook handler. |
273 | */ |
274 | } |
275 | |
276 | /* This function will be called from each arch-defined trampoline. */ |
277 | unsigned long rethook_trampoline_handler(struct pt_regs *regs, |
278 | unsigned long frame) |
279 | { |
280 | struct llist_node *first, *node = NULL; |
281 | unsigned long correct_ret_addr; |
282 | rethook_handler_t handler; |
283 | struct rethook_node *rhn; |
284 | |
285 | correct_ret_addr = __rethook_find_ret_addr(current, cur: &node); |
286 | if (!correct_ret_addr) { |
287 | pr_err("rethook: Return address not found! Maybe there is a bug in the kernel\n" ); |
288 | BUG_ON(1); |
289 | } |
290 | |
291 | instruction_pointer_set(regs, val: correct_ret_addr); |
292 | |
293 | /* |
294 | * These loops must be protected from rethook_free_rcu() because those |
295 | * are accessing 'rhn->rethook'. |
296 | */ |
297 | preempt_disable_notrace(); |
298 | |
299 | /* |
300 | * Run the handler on the shadow stack. Do not unlink the list here because |
301 | * stackdump inside the handlers needs to decode it. |
302 | */ |
303 | first = current->rethooks.first; |
304 | while (first) { |
305 | rhn = container_of(first, struct rethook_node, llist); |
306 | if (WARN_ON_ONCE(rhn->frame != frame)) |
307 | break; |
308 | handler = rethook_get_handler(rh: rhn->rethook); |
309 | if (handler) |
310 | handler(rhn, rhn->rethook->data, |
311 | correct_ret_addr, regs); |
312 | |
313 | if (first == node) |
314 | break; |
315 | first = first->next; |
316 | } |
317 | |
318 | /* Fixup registers for returning to correct address. */ |
319 | arch_rethook_fixup_return(regs, correct_ret_addr); |
320 | |
321 | /* Unlink used shadow stack */ |
322 | first = current->rethooks.first; |
323 | current->rethooks.first = node->next; |
324 | node->next = NULL; |
325 | |
326 | while (first) { |
327 | rhn = container_of(first, struct rethook_node, llist); |
328 | first = first->next; |
329 | rethook_recycle(node: rhn); |
330 | } |
331 | preempt_enable_notrace(); |
332 | |
333 | return correct_ret_addr; |
334 | } |
335 | NOKPROBE_SYMBOL(rethook_trampoline_handler); |
336 | |