kernel/bpf/ringbuf.c

   1 #include <linux/bpf.h>
   2 #include <linux/btf.h>
   3 #include <linux/err.h>
   4 #include <linux/irq_work.h>
   5 #include <linux/slab.h>
   6 #include <linux/filter.h>
   7 #include <linux/mm.h>
   8 #include <linux/vmalloc.h>
   9 #include <linux/wait.h>
  10 #include <linux/poll.h>
  11 #include <uapi/linux/btf.h>
  12
  13 #define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE)
  14
  15 /* non-mmap()'able part of bpf_ringbuf (everything up to consumer page) */
  16 #define RINGBUF_PGOFF \
  17         (offsetof(struct bpf_ringbuf, consumer_pos) >> PAGE_SHIFT)
  18 /* consumer page and producer page */
  19 #define RINGBUF_POS_PAGES 2
  20
  21 #define RINGBUF_MAX_RECORD_SZ (UINT_MAX/4)
  22
  23 /* Maximum size of ring buffer area is limited by 32-bit page offset within
  24  * record header, counted in pages. Reserve 8 bits for extensibility, and take
  25  * into account few extra pages for consumer/producer pages and
  26  * non-mmap()'able parts. This gives 64GB limit, which seems plenty for single
  27  * ring buffer.
  28  */
  29 #define RINGBUF_MAX_DATA_SZ \
  30         (((1ULL << 24) - RINGBUF_POS_PAGES - RINGBUF_PGOFF) * PAGE_SIZE)
  31
  32 struct bpf_ringbuf {
  33         wait_queue_head_t waitq;
  34         struct irq_work work;
  35         u64 mask;
  36         struct page **pages;
  37         int nr_pages;
  38         spinlock_t spinlock ____cacheline_aligned_in_smp;
  39         /* Consumer and producer counters are put into separate pages to allow
  40          * mapping consumer page as r/w, but restrict producer page to r/o.
  41          * This protects producer position from being modified by user-space
  42          * application and ruining in-kernel position tracking.
  43          */
  44         unsigned long consumer_pos __aligned(PAGE_SIZE);
  45         unsigned long producer_pos __aligned(PAGE_SIZE);
  46         char data[] __aligned(PAGE_SIZE);
  47 };
  48
  49 struct bpf_ringbuf_map {
  50         struct bpf_map map;
  51         struct bpf_ringbuf *rb;
  52 };
  53
  54 /* 8-byte ring buffer record header structure */
  55 struct bpf_ringbuf_hdr {
  56         u32 len;
  57         u32 pg_off;
  58 };
  59
  60 static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
  61 {
  62         const gfp_t flags = GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL |
  63                             __GFP_NOWARN | __GFP_ZERO;
  64         int nr_meta_pages = RINGBUF_PGOFF + RINGBUF_POS_PAGES;
  65         int nr_data_pages = data_sz >> PAGE_SHIFT;
  66         int nr_pages = nr_meta_pages + nr_data_pages;
  67         struct page **pages, *page;
  68         struct bpf_ringbuf *rb;
  69         size_t array_size;
  70         int i;
  71
  72         /* Each data page is mapped twice to allow "virtual"
  73          * continuous read of samples wrapping around the end of ring
  74          * buffer area:
  75          * ------------------------------------------------------
  76          * | meta pages |  real data pages  |  same data pages  |
  77          * ------------------------------------------------------
  78          * |            | 1 2 3 4 5 6 7 8 9 | 1 2 3 4 5 6 7 8 9 |
  79          * ------------------------------------------------------
  80          * |            | TA             DA | TA             DA |
  81          * ------------------------------------------------------
  82          *                               ^^^^^^^
  83          *                                  |
  84          * Here, no need to worry about special handling of wrapped-around
  85          * data due to double-mapped data pages. This works both in kernel and
  86          * when mmap()'ed in user-space, simplifying both kernel and
  87          * user-space implementations significantly.
  88          */
  89         array_size = (nr_meta_pages + 2 * nr_data_pages) * sizeof(*pages);
  90         pages = bpf_map_area_alloc(array_size, numa_node);
  91         if (!pages)
  92                 return NULL;
  93
  94         for (i = 0; i < nr_pages; i++) {
  95                 page = alloc_pages_node(numa_node, flags, 0);
  96                 if (!page) {
  97                         nr_pages = i;
  98                         goto err_free_pages;
  99                 }
 100                 pages[i] = page;
 101                 if (i >= nr_meta_pages)
 102                         pages[nr_data_pages + i] = page;
 103         }
 104
 105         rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages,
 106                   VM_ALLOC | VM_USERMAP, PAGE_KERNEL);
 107         if (rb) {
 108                 rb->pages = pages;
 109                 rb->nr_pages = nr_pages;
 110                 return rb;
 111         }
 112
 113 err_free_pages:
 114         for (i = 0; i < nr_pages; i++)
 115                 __free_page(pages[i]);
 116         kvfree(pages);
 117         return NULL;
 118 }
 119
 120 static void bpf_ringbuf_notify(struct irq_work *work)
 121 {
 122         struct bpf_ringbuf *rb = container_of(work, struct bpf_ringbuf, work);
 123
 124         wake_up_all(&rb->waitq);
 125 }
 126
 127 static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
 128 {
 129         struct bpf_ringbuf *rb;
 130
 131         rb = bpf_ringbuf_area_alloc(data_sz, numa_node);
 132         if (!rb)
 133                 return NULL;
 134
 135         spin_lock_init(&rb->spinlock);
 136         init_waitqueue_head(&rb->waitq);
 137         init_irq_work(&rb->work, bpf_ringbuf_notify);
 138
 139         rb->mask = data_sz - 1;
 140         rb->consumer_pos = 0;
 141         rb->producer_pos = 0;
 142
 143         return rb;
 144 }
 145
 146 static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
 147 {
 148         struct bpf_ringbuf_map *rb_map;
 149
 150         if (attr->map_flags & ~RINGBUF_CREATE_FLAG_MASK)
 151                 return ERR_PTR(-EINVAL);
 152
 153         if (attr->key_size || attr->value_size ||
 154             !is_power_of_2(attr->max_entries) ||
 155             !PAGE_ALIGNED(attr->max_entries))
 156                 return ERR_PTR(-EINVAL);
 157
 158 #ifdef CONFIG_64BIT
 159         /* on 32-bit arch, it's impossible to overflow record's hdr->pgoff */
 160         if (attr->max_entries > RINGBUF_MAX_DATA_SZ)
 161                 return ERR_PTR(-E2BIG);
 162 #endif
 163
 164         rb_map = kzalloc(sizeof(*rb_map), GFP_USER | __GFP_ACCOUNT);
 165         if (!rb_map)
 166                 return ERR_PTR(-ENOMEM);
 167
 168         bpf_map_init_from_attr(&rb_map->map, attr);
 169
 170         rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node);
 171         if (!rb_map->rb) {
 172                 kfree(rb_map);
 173                 return ERR_PTR(-ENOMEM);
 174         }
 175
 176         return &rb_map->map;
 177 }
 178
 179 static void bpf_ringbuf_free(struct bpf_ringbuf *rb)
 180 {
 181         /* copy pages pointer and nr_pages to local variable, as we are going
 182          * to unmap rb itself with vunmap() below
 183          */
 184         struct page **pages = rb->pages;
 185         int i, nr_pages = rb->nr_pages;
 186
 187         vunmap(rb);
 188         for (i = 0; i < nr_pages; i++)
 189                 __free_page(pages[i]);
 190         kvfree(pages);
 191 }
 192
 193 static void ringbuf_map_free(struct bpf_map *map)
 194 {
 195         struct bpf_ringbuf_map *rb_map;
 196
 197         rb_map = container_of(map, struct bpf_ringbuf_map, map);
 198         bpf_ringbuf_free(rb_map->rb);
 199         kfree(rb_map);
 200 }
 201
 202 static void *ringbuf_map_lookup_elem(struct bpf_map *map, void *key)
 203 {
 204         return ERR_PTR(-ENOTSUPP);
 205 }
 206
 207 static int ringbuf_map_update_elem(struct bpf_map *map, void *key, void *value,
 208                                    u64 flags)
 209 {
 210         return -ENOTSUPP;
 211 }
 212
 213 static int ringbuf_map_delete_elem(struct bpf_map *map, void *key)
 214 {
 215         return -ENOTSUPP;
 216 }
 217
 218 static int ringbuf_map_get_next_key(struct bpf_map *map, void *key,
 219                                     void *next_key)
 220 {
 221         return -ENOTSUPP;
 222 }
 223
 224 static size_t bpf_ringbuf_mmap_page_cnt(const struct bpf_ringbuf *rb)
 225 {
 226         size_t data_pages = (rb->mask + 1) >> PAGE_SHIFT;
 227
 228         /* consumer page + producer page + 2 x data pages */
 229         return RINGBUF_POS_PAGES + 2 * data_pages;
 230 }
 231
 232 static int ringbuf_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
 233 {
 234         struct bpf_ringbuf_map *rb_map;
 235         size_t mmap_sz;
 236
 237         rb_map = container_of(map, struct bpf_ringbuf_map, map);
 238         mmap_sz = bpf_ringbuf_mmap_page_cnt(rb_map->rb) << PAGE_SHIFT;
 239
 240         if (vma->vm_pgoff * PAGE_SIZE + (vma->vm_end - vma->vm_start) > mmap_sz)
 241                 return -EINVAL;
 242
 243         return remap_vmalloc_range(vma, rb_map->rb,
 244                                    vma->vm_pgoff + RINGBUF_PGOFF);
 245 }
 246
 247 static unsigned long ringbuf_avail_data_sz(struct bpf_ringbuf *rb)
 248 {
 249         unsigned long cons_pos, prod_pos;
 250
 251         cons_pos = smp_load_acquire(&rb->consumer_pos);
 252         prod_pos = smp_load_acquire(&rb->producer_pos);
 253         return prod_pos - cons_pos;
 254 }
 255
 256 static __poll_t ringbuf_map_poll(struct bpf_map *map, struct file *filp,
 257                                  struct poll_table_struct *pts)
 258 {
 259         struct bpf_ringbuf_map *rb_map;
 260
 261         rb_map = container_of(map, struct bpf_ringbuf_map, map);
 262         poll_wait(filp, &rb_map->rb->waitq, pts);
 263
 264         if (ringbuf_avail_data_sz(rb_map->rb))
 265                 return EPOLLIN | EPOLLRDNORM;
 266         return 0;
 267 }
 268
 269 static int ringbuf_map_btf_id;
 270 const struct bpf_map_ops ringbuf_map_ops = {
 271         .map_meta_equal = bpf_map_meta_equal,
 272         .map_alloc = ringbuf_map_alloc,
 273         .map_free = ringbuf_map_free,
 274         .map_mmap = ringbuf_map_mmap,
 275         .map_poll = ringbuf_map_poll,
 276         .map_lookup_elem = ringbuf_map_lookup_elem,
 277         .map_update_elem = ringbuf_map_update_elem,
 278         .map_delete_elem = ringbuf_map_delete_elem,
 279         .map_get_next_key = ringbuf_map_get_next_key,
 280         .map_btf_name = "bpf_ringbuf_map",
 281         .map_btf_id = &ringbuf_map_btf_id,
 282 };
 283
 284 /* Given pointer to ring buffer record metadata and struct bpf_ringbuf itself,
 285  * calculate offset from record metadata to ring buffer in pages, rounded
 286  * down. This page offset is stored as part of record metadata and allows to
 287  * restore struct bpf_ringbuf * from record pointer. This page offset is
 288  * stored at offset 4 of record metadata header.
 289  */
 290 static size_t bpf_ringbuf_rec_pg_off(struct bpf_ringbuf *rb,
 291                                      struct bpf_ringbuf_hdr *hdr)
 292 {
 293         return ((void *)hdr - (void *)rb) >> PAGE_SHIFT;
 294 }
 295
 296 /* Given pointer to ring buffer record header, restore pointer to struct
 297  * bpf_ringbuf itself by using page offset stored at offset 4
 298  */
 299 static struct bpf_ringbuf *
 300 bpf_ringbuf_restore_from_rec(struct bpf_ringbuf_hdr *hdr)
 301 {
 302         unsigned long addr = (unsigned long)(void *)hdr;
 303         unsigned long off = (unsigned long)hdr->pg_off << PAGE_SHIFT;
 304
 305         return (void*)((addr & PAGE_MASK) - off);
 306 }
 307
 308 static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
 309 {
 310         unsigned long cons_pos, prod_pos, new_prod_pos, flags;
 311         u32 len, pg_off;
 312         struct bpf_ringbuf_hdr *hdr;
 313
 314         if (unlikely(size > RINGBUF_MAX_RECORD_SZ))
 315                 return NULL;
 316
 317         len = round_up(size + BPF_RINGBUF_HDR_SZ, 8);
 318         cons_pos = smp_load_acquire(&rb->consumer_pos);
 319
 320         if (in_nmi()) {
 321                 if (!spin_trylock_irqsave(&rb->spinlock, flags))
 322                         return NULL;
 323         } else {
 324                 spin_lock_irqsave(&rb->spinlock, flags);
 325         }
 326
 327         prod_pos = rb->producer_pos;
 328         new_prod_pos = prod_pos + len;
 329
 330         /* check for out of ringbuf space by ensuring producer position
 331          * doesn't advance more than (ringbuf_size - 1) ahead
 332          */
 333         if (new_prod_pos - cons_pos > rb->mask) {
 334                 spin_unlock_irqrestore(&rb->spinlock, flags);
 335                 return NULL;
 336         }
 337
 338         hdr = (void *)rb->data + (prod_pos & rb->mask);
 339         pg_off = bpf_ringbuf_rec_pg_off(rb, hdr);
 340         hdr->len = size | BPF_RINGBUF_BUSY_BIT;
 341         hdr->pg_off = pg_off;
 342
 343         /* pairs with consumer's smp_load_acquire() */
 344         smp_store_release(&rb->producer_pos, new_prod_pos);
 345
 346         spin_unlock_irqrestore(&rb->spinlock, flags);
 347
 348         return (void *)hdr + BPF_RINGBUF_HDR_SZ;
 349 }
 350
 351 BPF_CALL_3(bpf_ringbuf_reserve, struct bpf_map *, map, u64, size, u64, flags)
 352 {
 353         struct bpf_ringbuf_map *rb_map;
 354
 355         if (unlikely(flags))
 356                 return 0;
 357
 358         rb_map = container_of(map, struct bpf_ringbuf_map, map);
 359         return (unsigned long)__bpf_ringbuf_reserve(rb_map->rb, size);
 360 }
 361
 362 const struct bpf_func_proto bpf_ringbuf_reserve_proto = {
 363         .func           = bpf_ringbuf_reserve,
 364         .ret_type       = RET_PTR_TO_ALLOC_MEM_OR_NULL,
 365         .arg1_type      = ARG_CONST_MAP_PTR,
 366         .arg2_type      = ARG_CONST_ALLOC_SIZE_OR_ZERO,
 367         .arg3_type      = ARG_ANYTHING,
 368 };
 369
 370 static void bpf_ringbuf_commit(void *sample, u64 flags, bool discard)
 371 {
 372         unsigned long rec_pos, cons_pos;
 373         struct bpf_ringbuf_hdr *hdr;
 374         struct bpf_ringbuf *rb;
 375         u32 new_len;
 376
 377         hdr = sample - BPF_RINGBUF_HDR_SZ;
 378         rb = bpf_ringbuf_restore_from_rec(hdr);
 379         new_len = hdr->len ^ BPF_RINGBUF_BUSY_BIT;
 380         if (discard)
 381                 new_len |= BPF_RINGBUF_DISCARD_BIT;
 382
 383         /* update record header with correct final size prefix */
 384         xchg(&hdr->len, new_len);
 385
 386         /* if consumer caught up and is waiting for our record, notify about
 387          * new data availability
 388          */
 389         rec_pos = (void *)hdr - (void *)rb->data;
 390         cons_pos = smp_load_acquire(&rb->consumer_pos) & rb->mask;
 391
 392         if (flags & BPF_RB_FORCE_WAKEUP)
 393                 irq_work_queue(&rb->work);
 394         else if (cons_pos == rec_pos && !(flags & BPF_RB_NO_WAKEUP))
 395                 irq_work_queue(&rb->work);
 396 }
 397
 398 BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
 399 {
 400         bpf_ringbuf_commit(sample, flags, false /* discard */);
 401         return 0;
 402 }
 403
 404 const struct bpf_func_proto bpf_ringbuf_submit_proto = {
 405         .func           = bpf_ringbuf_submit,
 406         .ret_type       = RET_VOID,
 407         .arg1_type      = ARG_PTR_TO_ALLOC_MEM,
 408         .arg2_type      = ARG_ANYTHING,
 409 };
 410
 411 BPF_CALL_2(bpf_ringbuf_discard, void *, sample, u64, flags)
 412 {
 413         bpf_ringbuf_commit(sample, flags, true /* discard */);
 414         return 0;
 415 }
 416
 417 const struct bpf_func_proto bpf_ringbuf_discard_proto = {
 418         .func           = bpf_ringbuf_discard,
 419         .ret_type       = RET_VOID,
 420         .arg1_type      = ARG_PTR_TO_ALLOC_MEM,
 421         .arg2_type      = ARG_ANYTHING,
 422 };
 423
 424 BPF_CALL_4(bpf_ringbuf_output, struct bpf_map *, map, void *, data, u64, size,
 425            u64, flags)
 426 {
 427         struct bpf_ringbuf_map *rb_map;
 428         void *rec;
 429
 430         if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
 431                 return -EINVAL;
 432
 433         rb_map = container_of(map, struct bpf_ringbuf_map, map);
 434         rec = __bpf_ringbuf_reserve(rb_map->rb, size);
 435         if (!rec)
 436                 return -EAGAIN;
 437
 438         memcpy(rec, data, size);
 439         bpf_ringbuf_commit(rec, flags, false /* discard */);
 440         return 0;
 441 }
 442
 443 const struct bpf_func_proto bpf_ringbuf_output_proto = {
 444         .func           = bpf_ringbuf_output,
 445         .ret_type       = RET_INTEGER,
 446         .arg1_type      = ARG_CONST_MAP_PTR,
 447         .arg2_type      = ARG_PTR_TO_MEM,
 448         .arg3_type      = ARG_CONST_SIZE_OR_ZERO,
 449         .arg4_type      = ARG_ANYTHING,
 450 };
 451
 452 BPF_CALL_2(bpf_ringbuf_query, struct bpf_map *, map, u64, flags)
 453 {
 454         struct bpf_ringbuf *rb;
 455
 456         rb = container_of(map, struct bpf_ringbuf_map, map)->rb;
 457
 458         switch (flags) {
 459         case BPF_RB_AVAIL_DATA:
 460                 return ringbuf_avail_data_sz(rb);
 461         case BPF_RB_RING_SIZE:
 462                 return rb->mask + 1;
 463         case BPF_RB_CONS_POS:
 464                 return smp_load_acquire(&rb->consumer_pos);
 465         case BPF_RB_PROD_POS:
 466                 return smp_load_acquire(&rb->producer_pos);
 467         default:
 468                 return 0;
 469         }
 470 }
 471
 472 const struct bpf_func_proto bpf_ringbuf_query_proto = {
 473         .func           = bpf_ringbuf_query,
 474         .ret_type       = RET_INTEGER,
 475         .arg1_type      = ARG_CONST_MAP_PTR,
 476         .arg2_type      = ARG_ANYTHING,
 477 };