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