1 // SPDX-License-Identifier: GPL-2.0-only 2 3 /* 4 * HID-BPF support for Linux 5 * 6 * Copyright (c) 2022 Benjamin Tissoires 7 */ 8 9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 10 #include <linux/bitops.h> 11 #include <linux/btf.h> 12 #include <linux/btf_ids.h> 13 #include <linux/filter.h> 14 #include <linux/hid.h> 15 #include <linux/hid_bpf.h> 16 #include <linux/init.h> 17 #include <linux/kfifo.h> 18 #include <linux/minmax.h> 19 #include <linux/module.h> 20 #include <linux/workqueue.h> 21 #include "hid_bpf_dispatch.h" 22 #include "entrypoints/entrypoints.lskel.h" 23 24 struct hid_bpf_ops *hid_bpf_ops; 25 EXPORT_SYMBOL(hid_bpf_ops); 26 27 /** 28 * hid_bpf_device_event - Called whenever an event is coming in from the device 29 * 30 * @ctx: The HID-BPF context 31 * 32 * @return %0 on success and keep processing; a positive value to change the 33 * incoming size buffer; a negative error code to interrupt the processing 34 * of this event 35 * 36 * Declare an %fmod_ret tracing bpf program to this function and attach this 37 * program through hid_bpf_attach_prog() to have this helper called for 38 * any incoming event from the device itself. 39 * 40 * The function is called while on IRQ context, so we can not sleep. 41 */ 42 /* never used by the kernel but declared so we can load and attach a tracepoint */ 43 __weak noinline int hid_bpf_device_event(struct hid_bpf_ctx *ctx) 44 { 45 return 0; 46 } 47 48 u8 * 49 dispatch_hid_bpf_device_event(struct hid_device *hdev, enum hid_report_type type, u8 *data, 50 u32 *size, int interrupt) 51 { 52 struct hid_bpf_ctx_kern ctx_kern = { 53 .ctx = { 54 .hid = hdev, 55 .report_type = type, 56 .allocated_size = hdev->bpf.allocated_data, 57 .size = *size, 58 }, 59 .data = hdev->bpf.device_data, 60 }; 61 int ret; 62 63 if (type >= HID_REPORT_TYPES) 64 return ERR_PTR(-EINVAL); 65 66 /* no program has been attached yet */ 67 if (!hdev->bpf.device_data) 68 return data; 69 70 memset(ctx_kern.data, 0, hdev->bpf.allocated_data); 71 memcpy(ctx_kern.data, data, *size); 72 73 ret = hid_bpf_prog_run(hdev, HID_BPF_PROG_TYPE_DEVICE_EVENT, &ctx_kern); 74 if (ret < 0) 75 return ERR_PTR(ret); 76 77 if (ret) { 78 if (ret > ctx_kern.ctx.allocated_size) 79 return ERR_PTR(-EINVAL); 80 81 *size = ret; 82 } 83 84 return ctx_kern.data; 85 } 86 EXPORT_SYMBOL_GPL(dispatch_hid_bpf_device_event); 87 88 /** 89 * hid_bpf_rdesc_fixup - Called when the probe function parses the report 90 * descriptor of the HID device 91 * 92 * @ctx: The HID-BPF context 93 * 94 * @return 0 on success and keep processing; a positive value to change the 95 * incoming size buffer; a negative error code to interrupt the processing 96 * of this event 97 * 98 * Declare an %fmod_ret tracing bpf program to this function and attach this 99 * program through hid_bpf_attach_prog() to have this helper called before any 100 * parsing of the report descriptor by HID. 101 */ 102 /* never used by the kernel but declared so we can load and attach a tracepoint */ 103 __weak noinline int hid_bpf_rdesc_fixup(struct hid_bpf_ctx *ctx) 104 { 105 return 0; 106 } 107 108 u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size) 109 { 110 int ret; 111 struct hid_bpf_ctx_kern ctx_kern = { 112 .ctx = { 113 .hid = hdev, 114 .size = *size, 115 .allocated_size = HID_MAX_DESCRIPTOR_SIZE, 116 }, 117 }; 118 119 ctx_kern.data = kzalloc(ctx_kern.ctx.allocated_size, GFP_KERNEL); 120 if (!ctx_kern.data) 121 goto ignore_bpf; 122 123 memcpy(ctx_kern.data, rdesc, min_t(unsigned int, *size, HID_MAX_DESCRIPTOR_SIZE)); 124 125 ret = hid_bpf_prog_run(hdev, HID_BPF_PROG_TYPE_RDESC_FIXUP, &ctx_kern); 126 if (ret < 0) 127 goto ignore_bpf; 128 129 if (ret) { 130 if (ret > ctx_kern.ctx.allocated_size) 131 goto ignore_bpf; 132 133 *size = ret; 134 } 135 136 rdesc = krealloc(ctx_kern.data, *size, GFP_KERNEL); 137 138 return rdesc; 139 140 ignore_bpf: 141 kfree(ctx_kern.data); 142 return kmemdup(rdesc, *size, GFP_KERNEL); 143 } 144 EXPORT_SYMBOL_GPL(call_hid_bpf_rdesc_fixup); 145 146 /** 147 * hid_bpf_get_data - Get the kernel memory pointer associated with the context @ctx 148 * 149 * @ctx: The HID-BPF context 150 * @offset: The offset within the memory 151 * @rdwr_buf_size: the const size of the buffer 152 * 153 * @returns %NULL on error, an %__u8 memory pointer on success 154 */ 155 noinline __u8 * 156 hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t rdwr_buf_size) 157 { 158 struct hid_bpf_ctx_kern *ctx_kern; 159 160 if (!ctx) 161 return NULL; 162 163 ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx); 164 165 if (rdwr_buf_size + offset > ctx->allocated_size) 166 return NULL; 167 168 return ctx_kern->data + offset; 169 } 170 171 /* 172 * The following set contains all functions we agree BPF programs 173 * can use. 174 */ 175 BTF_SET8_START(hid_bpf_kfunc_ids) 176 BTF_ID_FLAGS(func, hid_bpf_get_data, KF_RET_NULL) 177 BTF_SET8_END(hid_bpf_kfunc_ids) 178 179 static const struct btf_kfunc_id_set hid_bpf_kfunc_set = { 180 .owner = THIS_MODULE, 181 .set = &hid_bpf_kfunc_ids, 182 }; 183 184 static int device_match_id(struct device *dev, const void *id) 185 { 186 struct hid_device *hdev = to_hid_device(dev); 187 188 return hdev->id == *(int *)id; 189 } 190 191 static int __hid_bpf_allocate_data(struct hid_device *hdev, u8 **data, u32 *size) 192 { 193 u8 *alloc_data; 194 unsigned int i, j, max_report_len = 0; 195 size_t alloc_size = 0; 196 197 /* compute the maximum report length for this device */ 198 for (i = 0; i < HID_REPORT_TYPES; i++) { 199 struct hid_report_enum *report_enum = hdev->report_enum + i; 200 201 for (j = 0; j < HID_MAX_IDS; j++) { 202 struct hid_report *report = report_enum->report_id_hash[j]; 203 204 if (report) 205 max_report_len = max(max_report_len, hid_report_len(report)); 206 } 207 } 208 209 /* 210 * Give us a little bit of extra space and some predictability in the 211 * buffer length we create. This way, we can tell users that they can 212 * work on chunks of 64 bytes of memory without having the bpf verifier 213 * scream at them. 214 */ 215 alloc_size = DIV_ROUND_UP(max_report_len, 64) * 64; 216 217 alloc_data = kzalloc(alloc_size, GFP_KERNEL); 218 if (!alloc_data) 219 return -ENOMEM; 220 221 *data = alloc_data; 222 *size = alloc_size; 223 224 return 0; 225 } 226 227 static int hid_bpf_allocate_event_data(struct hid_device *hdev) 228 { 229 /* hdev->bpf.device_data is already allocated, abort */ 230 if (hdev->bpf.device_data) 231 return 0; 232 233 return __hid_bpf_allocate_data(hdev, &hdev->bpf.device_data, &hdev->bpf.allocated_data); 234 } 235 236 int hid_bpf_reconnect(struct hid_device *hdev) 237 { 238 if (!test_and_set_bit(ffs(HID_STAT_REPROBED), &hdev->status)) 239 return device_reprobe(&hdev->dev); 240 241 return 0; 242 } 243 244 static int do_hid_bpf_attach_prog(struct hid_device *hdev, int prog_fd, struct bpf_prog *prog, 245 __u32 flags) 246 { 247 int fd, err, prog_type; 248 249 prog_type = hid_bpf_get_prog_attach_type(prog); 250 if (prog_type < 0) 251 return prog_type; 252 253 if (prog_type >= HID_BPF_PROG_TYPE_MAX) 254 return -EINVAL; 255 256 if (prog_type == HID_BPF_PROG_TYPE_DEVICE_EVENT) { 257 err = hid_bpf_allocate_event_data(hdev); 258 if (err) 259 return err; 260 } 261 262 fd = __hid_bpf_attach_prog(hdev, prog_type, prog_fd, prog, flags); 263 if (fd < 0) 264 return fd; 265 266 if (prog_type == HID_BPF_PROG_TYPE_RDESC_FIXUP) { 267 err = hid_bpf_reconnect(hdev); 268 if (err) { 269 close_fd(fd); 270 return err; 271 } 272 } 273 274 return fd; 275 } 276 277 /** 278 * hid_bpf_attach_prog - Attach the given @prog_fd to the given HID device 279 * 280 * @hid_id: the system unique identifier of the HID device 281 * @prog_fd: an fd in the user process representing the program to attach 282 * @flags: any logical OR combination of &enum hid_bpf_attach_flags 283 * 284 * @returns an fd of a bpf_link object on success (> %0), an error code otherwise. 285 * Closing this fd will detach the program from the HID device (unless the bpf_link 286 * is pinned to the BPF file system). 287 */ 288 /* called from syscall */ 289 noinline int 290 hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags) 291 { 292 struct hid_device *hdev; 293 struct bpf_prog *prog; 294 struct device *dev; 295 int fd; 296 297 if (!hid_bpf_ops) 298 return -EINVAL; 299 300 if ((flags & ~HID_BPF_FLAG_MASK)) 301 return -EINVAL; 302 303 dev = bus_find_device(hid_bpf_ops->bus_type, NULL, &hid_id, device_match_id); 304 if (!dev) 305 return -EINVAL; 306 307 hdev = to_hid_device(dev); 308 309 /* 310 * take a ref on the prog itself, it will be released 311 * on errors or when it'll be detached 312 */ 313 prog = bpf_prog_get(prog_fd); 314 if (IS_ERR(prog)) 315 return PTR_ERR(prog); 316 317 fd = do_hid_bpf_attach_prog(hdev, prog_fd, prog, flags); 318 if (fd < 0) 319 bpf_prog_put(prog); 320 321 return fd; 322 } 323 324 /** 325 * hid_bpf_allocate_context - Allocate a context to the given HID device 326 * 327 * @hid_id: the system unique identifier of the HID device 328 * 329 * @returns A pointer to &struct hid_bpf_ctx on success, %NULL on error. 330 */ 331 noinline struct hid_bpf_ctx * 332 hid_bpf_allocate_context(unsigned int hid_id) 333 { 334 struct hid_device *hdev; 335 struct hid_bpf_ctx_kern *ctx_kern = NULL; 336 struct device *dev; 337 338 if (!hid_bpf_ops) 339 return NULL; 340 341 dev = bus_find_device(hid_bpf_ops->bus_type, NULL, &hid_id, device_match_id); 342 if (!dev) 343 return NULL; 344 345 hdev = to_hid_device(dev); 346 347 ctx_kern = kzalloc(sizeof(*ctx_kern), GFP_KERNEL); 348 if (!ctx_kern) 349 return NULL; 350 351 ctx_kern->ctx.hid = hdev; 352 353 return &ctx_kern->ctx; 354 } 355 356 /** 357 * hid_bpf_release_context - Release the previously allocated context @ctx 358 * 359 * @ctx: the HID-BPF context to release 360 * 361 */ 362 noinline void 363 hid_bpf_release_context(struct hid_bpf_ctx *ctx) 364 { 365 struct hid_bpf_ctx_kern *ctx_kern; 366 367 ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx); 368 369 kfree(ctx_kern); 370 } 371 372 /** 373 * hid_bpf_hw_request - Communicate with a HID device 374 * 375 * @ctx: the HID-BPF context previously allocated in hid_bpf_allocate_context() 376 * @buf: a %PTR_TO_MEM buffer 377 * @buf__sz: the size of the data to transfer 378 * @rtype: the type of the report (%HID_INPUT_REPORT, %HID_FEATURE_REPORT, %HID_OUTPUT_REPORT) 379 * @reqtype: the type of the request (%HID_REQ_GET_REPORT, %HID_REQ_SET_REPORT, ...) 380 * 381 * @returns %0 on success, a negative error code otherwise. 382 */ 383 noinline int 384 hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz, 385 enum hid_report_type rtype, enum hid_class_request reqtype) 386 { 387 struct hid_device *hdev; 388 struct hid_report *report; 389 struct hid_report_enum *report_enum; 390 u8 *dma_data; 391 u32 report_len; 392 int ret; 393 394 /* check arguments */ 395 if (!ctx || !hid_bpf_ops || !buf) 396 return -EINVAL; 397 398 switch (rtype) { 399 case HID_INPUT_REPORT: 400 case HID_OUTPUT_REPORT: 401 case HID_FEATURE_REPORT: 402 break; 403 default: 404 return -EINVAL; 405 } 406 407 switch (reqtype) { 408 case HID_REQ_GET_REPORT: 409 case HID_REQ_GET_IDLE: 410 case HID_REQ_GET_PROTOCOL: 411 case HID_REQ_SET_REPORT: 412 case HID_REQ_SET_IDLE: 413 case HID_REQ_SET_PROTOCOL: 414 break; 415 default: 416 return -EINVAL; 417 } 418 419 if (buf__sz < 1) 420 return -EINVAL; 421 422 hdev = (struct hid_device *)ctx->hid; /* discard const */ 423 424 report_enum = hdev->report_enum + rtype; 425 report = hid_bpf_ops->hid_get_report(report_enum, buf); 426 if (!report) 427 return -EINVAL; 428 429 report_len = hid_report_len(report); 430 431 if (buf__sz > report_len) 432 buf__sz = report_len; 433 434 dma_data = kmemdup(buf, buf__sz, GFP_KERNEL); 435 if (!dma_data) 436 return -ENOMEM; 437 438 ret = hid_bpf_ops->hid_hw_raw_request(hdev, 439 dma_data[0], 440 dma_data, 441 buf__sz, 442 rtype, 443 reqtype); 444 445 if (ret > 0) 446 memcpy(buf, dma_data, ret); 447 448 kfree(dma_data); 449 return ret; 450 } 451 452 /* our HID-BPF entrypoints */ 453 BTF_SET8_START(hid_bpf_fmodret_ids) 454 BTF_ID_FLAGS(func, hid_bpf_device_event) 455 BTF_ID_FLAGS(func, hid_bpf_rdesc_fixup) 456 BTF_ID_FLAGS(func, __hid_bpf_tail_call) 457 BTF_SET8_END(hid_bpf_fmodret_ids) 458 459 static const struct btf_kfunc_id_set hid_bpf_fmodret_set = { 460 .owner = THIS_MODULE, 461 .set = &hid_bpf_fmodret_ids, 462 }; 463 464 /* for syscall HID-BPF */ 465 BTF_SET8_START(hid_bpf_syscall_kfunc_ids) 466 BTF_ID_FLAGS(func, hid_bpf_attach_prog) 467 BTF_ID_FLAGS(func, hid_bpf_allocate_context, KF_ACQUIRE | KF_RET_NULL) 468 BTF_ID_FLAGS(func, hid_bpf_release_context, KF_RELEASE) 469 BTF_ID_FLAGS(func, hid_bpf_hw_request) 470 BTF_SET8_END(hid_bpf_syscall_kfunc_ids) 471 472 static const struct btf_kfunc_id_set hid_bpf_syscall_kfunc_set = { 473 .owner = THIS_MODULE, 474 .set = &hid_bpf_syscall_kfunc_ids, 475 }; 476 477 int hid_bpf_connect_device(struct hid_device *hdev) 478 { 479 struct hid_bpf_prog_list *prog_list; 480 481 rcu_read_lock(); 482 prog_list = rcu_dereference(hdev->bpf.progs[HID_BPF_PROG_TYPE_DEVICE_EVENT]); 483 rcu_read_unlock(); 484 485 /* only allocate BPF data if there are programs attached */ 486 if (!prog_list) 487 return 0; 488 489 return hid_bpf_allocate_event_data(hdev); 490 } 491 EXPORT_SYMBOL_GPL(hid_bpf_connect_device); 492 493 void hid_bpf_disconnect_device(struct hid_device *hdev) 494 { 495 kfree(hdev->bpf.device_data); 496 hdev->bpf.device_data = NULL; 497 hdev->bpf.allocated_data = 0; 498 } 499 EXPORT_SYMBOL_GPL(hid_bpf_disconnect_device); 500 501 void hid_bpf_destroy_device(struct hid_device *hdev) 502 { 503 if (!hdev) 504 return; 505 506 /* mark the device as destroyed in bpf so we don't reattach it */ 507 hdev->bpf.destroyed = true; 508 509 __hid_bpf_destroy_device(hdev); 510 } 511 EXPORT_SYMBOL_GPL(hid_bpf_destroy_device); 512 513 void hid_bpf_device_init(struct hid_device *hdev) 514 { 515 spin_lock_init(&hdev->bpf.progs_lock); 516 } 517 EXPORT_SYMBOL_GPL(hid_bpf_device_init); 518 519 static int __init hid_bpf_init(void) 520 { 521 int err; 522 523 /* Note: if we exit with an error any time here, we would entirely break HID, which 524 * is probably not something we want. So we log an error and return success. 525 * 526 * This is not a big deal: the syscall allowing to attach a BPF program to a HID device 527 * will not be available, so nobody will be able to use the functionality. 528 */ 529 530 err = register_btf_fmodret_id_set(&hid_bpf_fmodret_set); 531 if (err) { 532 pr_warn("error while registering fmodret entrypoints: %d", err); 533 return 0; 534 } 535 536 err = hid_bpf_preload_skel(); 537 if (err) { 538 pr_warn("error while preloading HID BPF dispatcher: %d", err); 539 return 0; 540 } 541 542 /* register tracing kfuncs after we are sure we can load our preloaded bpf program */ 543 err = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &hid_bpf_kfunc_set); 544 if (err) { 545 pr_warn("error while setting HID BPF tracing kfuncs: %d", err); 546 return 0; 547 } 548 549 /* register syscalls after we are sure we can load our preloaded bpf program */ 550 err = register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &hid_bpf_syscall_kfunc_set); 551 if (err) { 552 pr_warn("error while setting HID BPF syscall kfuncs: %d", err); 553 return 0; 554 } 555 556 return 0; 557 } 558 559 static void __exit hid_bpf_exit(void) 560 { 561 /* HID depends on us, so if we hit that code, we are guaranteed that hid 562 * has been removed and thus we do not need to clear the HID devices 563 */ 564 hid_bpf_free_links_and_skel(); 565 } 566 567 late_initcall(hid_bpf_init); 568 module_exit(hid_bpf_exit); 569 MODULE_AUTHOR("Benjamin Tissoires"); 570 MODULE_LICENSE("GPL"); 571