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linux-next/kernel/bpf/ringbuf.c
Andrii Nakryiko 517bbe1994 bpf: Enforce BPF ringbuf size to be the power of 2
BPF ringbuf assumes the size to be a multiple of page size and the power of
2 value. The latter is important to avoid division while calculating position
inside the ring buffer and using (N-1) mask instead. This patch fixes omission
to enforce power-of-2 size rule.

Fixes: 457f44363a ("bpf: Implement BPF ring buffer and verifier support for it")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200630061500.1804799-1-andriin@fb.com
2020-06-30 16:31:55 +02:00

500 lines
13 KiB
C

#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/err.h>
#include <linux/irq_work.h>
#include <linux/slab.h>
#include <linux/filter.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/wait.h>
#include <linux/poll.h>
#include <uapi/linux/btf.h>
#define RINGBUF_CREATE_FLAG_MASK (BPF_F_NUMA_NODE)
/* non-mmap()'able part of bpf_ringbuf (everything up to consumer page) */
#define RINGBUF_PGOFF \
(offsetof(struct bpf_ringbuf, consumer_pos) >> PAGE_SHIFT)
/* consumer page and producer page */
#define RINGBUF_POS_PAGES 2
#define RINGBUF_MAX_RECORD_SZ (UINT_MAX/4)
/* Maximum size of ring buffer area is limited by 32-bit page offset within
* record header, counted in pages. Reserve 8 bits for extensibility, and take
* into account few extra pages for consumer/producer pages and
* non-mmap()'able parts. This gives 64GB limit, which seems plenty for single
* ring buffer.
*/
#define RINGBUF_MAX_DATA_SZ \
(((1ULL << 24) - RINGBUF_POS_PAGES - RINGBUF_PGOFF) * PAGE_SIZE)
struct bpf_ringbuf {
wait_queue_head_t waitq;
struct irq_work work;
u64 mask;
struct page **pages;
int nr_pages;
spinlock_t spinlock ____cacheline_aligned_in_smp;
/* Consumer and producer counters are put into separate pages to allow
* mapping consumer page as r/w, but restrict producer page to r/o.
* This protects producer position from being modified by user-space
* application and ruining in-kernel position tracking.
*/
unsigned long consumer_pos __aligned(PAGE_SIZE);
unsigned long producer_pos __aligned(PAGE_SIZE);
char data[] __aligned(PAGE_SIZE);
};
struct bpf_ringbuf_map {
struct bpf_map map;
struct bpf_map_memory memory;
struct bpf_ringbuf *rb;
};
/* 8-byte ring buffer record header structure */
struct bpf_ringbuf_hdr {
u32 len;
u32 pg_off;
};
static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
{
const gfp_t flags = GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_NOWARN |
__GFP_ZERO;
int nr_meta_pages = RINGBUF_PGOFF + RINGBUF_POS_PAGES;
int nr_data_pages = data_sz >> PAGE_SHIFT;
int nr_pages = nr_meta_pages + nr_data_pages;
struct page **pages, *page;
struct bpf_ringbuf *rb;
size_t array_size;
int i;
/* Each data page is mapped twice to allow "virtual"
* continuous read of samples wrapping around the end of ring
* buffer area:
* ------------------------------------------------------
* | meta pages | real data pages | same data pages |
* ------------------------------------------------------
* | | 1 2 3 4 5 6 7 8 9 | 1 2 3 4 5 6 7 8 9 |
* ------------------------------------------------------
* | | TA DA | TA DA |
* ------------------------------------------------------
* ^^^^^^^
* |
* Here, no need to worry about special handling of wrapped-around
* data due to double-mapped data pages. This works both in kernel and
* when mmap()'ed in user-space, simplifying both kernel and
* user-space implementations significantly.
*/
array_size = (nr_meta_pages + 2 * nr_data_pages) * sizeof(*pages);
if (array_size > PAGE_SIZE)
pages = vmalloc_node(array_size, numa_node);
else
pages = kmalloc_node(array_size, flags, numa_node);
if (!pages)
return NULL;
for (i = 0; i < nr_pages; i++) {
page = alloc_pages_node(numa_node, flags, 0);
if (!page) {
nr_pages = i;
goto err_free_pages;
}
pages[i] = page;
if (i >= nr_meta_pages)
pages[nr_data_pages + i] = page;
}
rb = vmap(pages, nr_meta_pages + 2 * nr_data_pages,
VM_ALLOC | VM_USERMAP, PAGE_KERNEL);
if (rb) {
rb->pages = pages;
rb->nr_pages = nr_pages;
return rb;
}
err_free_pages:
for (i = 0; i < nr_pages; i++)
__free_page(pages[i]);
kvfree(pages);
return NULL;
}
static void bpf_ringbuf_notify(struct irq_work *work)
{
struct bpf_ringbuf *rb = container_of(work, struct bpf_ringbuf, work);
wake_up_all(&rb->waitq);
}
static struct bpf_ringbuf *bpf_ringbuf_alloc(size_t data_sz, int numa_node)
{
struct bpf_ringbuf *rb;
rb = bpf_ringbuf_area_alloc(data_sz, numa_node);
if (!rb)
return ERR_PTR(-ENOMEM);
spin_lock_init(&rb->spinlock);
init_waitqueue_head(&rb->waitq);
init_irq_work(&rb->work, bpf_ringbuf_notify);
rb->mask = data_sz - 1;
rb->consumer_pos = 0;
rb->producer_pos = 0;
return rb;
}
static struct bpf_map *ringbuf_map_alloc(union bpf_attr *attr)
{
struct bpf_ringbuf_map *rb_map;
u64 cost;
int err;
if (attr->map_flags & ~RINGBUF_CREATE_FLAG_MASK)
return ERR_PTR(-EINVAL);
if (attr->key_size || attr->value_size ||
!is_power_of_2(attr->max_entries) ||
!PAGE_ALIGNED(attr->max_entries))
return ERR_PTR(-EINVAL);
#ifdef CONFIG_64BIT
/* on 32-bit arch, it's impossible to overflow record's hdr->pgoff */
if (attr->max_entries > RINGBUF_MAX_DATA_SZ)
return ERR_PTR(-E2BIG);
#endif
rb_map = kzalloc(sizeof(*rb_map), GFP_USER);
if (!rb_map)
return ERR_PTR(-ENOMEM);
bpf_map_init_from_attr(&rb_map->map, attr);
cost = sizeof(struct bpf_ringbuf_map) +
sizeof(struct bpf_ringbuf) +
attr->max_entries;
err = bpf_map_charge_init(&rb_map->map.memory, cost);
if (err)
goto err_free_map;
rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node);
if (IS_ERR(rb_map->rb)) {
err = PTR_ERR(rb_map->rb);
goto err_uncharge;
}
return &rb_map->map;
err_uncharge:
bpf_map_charge_finish(&rb_map->map.memory);
err_free_map:
kfree(rb_map);
return ERR_PTR(err);
}
static void bpf_ringbuf_free(struct bpf_ringbuf *rb)
{
/* copy pages pointer and nr_pages to local variable, as we are going
* to unmap rb itself with vunmap() below
*/
struct page **pages = rb->pages;
int i, nr_pages = rb->nr_pages;
vunmap(rb);
for (i = 0; i < nr_pages; i++)
__free_page(pages[i]);
kvfree(pages);
}
static void ringbuf_map_free(struct bpf_map *map)
{
struct bpf_ringbuf_map *rb_map;
/* at this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
* so the programs (can be more than one that used this map) were
* disconnected from events. Wait for outstanding critical sections in
* these programs to complete
*/
synchronize_rcu();
rb_map = container_of(map, struct bpf_ringbuf_map, map);
bpf_ringbuf_free(rb_map->rb);
kfree(rb_map);
}
static void *ringbuf_map_lookup_elem(struct bpf_map *map, void *key)
{
return ERR_PTR(-ENOTSUPP);
}
static int ringbuf_map_update_elem(struct bpf_map *map, void *key, void *value,
u64 flags)
{
return -ENOTSUPP;
}
static int ringbuf_map_delete_elem(struct bpf_map *map, void *key)
{
return -ENOTSUPP;
}
static int ringbuf_map_get_next_key(struct bpf_map *map, void *key,
void *next_key)
{
return -ENOTSUPP;
}
static size_t bpf_ringbuf_mmap_page_cnt(const struct bpf_ringbuf *rb)
{
size_t data_pages = (rb->mask + 1) >> PAGE_SHIFT;
/* consumer page + producer page + 2 x data pages */
return RINGBUF_POS_PAGES + 2 * data_pages;
}
static int ringbuf_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
{
struct bpf_ringbuf_map *rb_map;
size_t mmap_sz;
rb_map = container_of(map, struct bpf_ringbuf_map, map);
mmap_sz = bpf_ringbuf_mmap_page_cnt(rb_map->rb) << PAGE_SHIFT;
if (vma->vm_pgoff * PAGE_SIZE + (vma->vm_end - vma->vm_start) > mmap_sz)
return -EINVAL;
return remap_vmalloc_range(vma, rb_map->rb,
vma->vm_pgoff + RINGBUF_PGOFF);
}
static unsigned long ringbuf_avail_data_sz(struct bpf_ringbuf *rb)
{
unsigned long cons_pos, prod_pos;
cons_pos = smp_load_acquire(&rb->consumer_pos);
prod_pos = smp_load_acquire(&rb->producer_pos);
return prod_pos - cons_pos;
}
static __poll_t ringbuf_map_poll(struct bpf_map *map, struct file *filp,
struct poll_table_struct *pts)
{
struct bpf_ringbuf_map *rb_map;
rb_map = container_of(map, struct bpf_ringbuf_map, map);
poll_wait(filp, &rb_map->rb->waitq, pts);
if (ringbuf_avail_data_sz(rb_map->rb))
return EPOLLIN | EPOLLRDNORM;
return 0;
}
const struct bpf_map_ops ringbuf_map_ops = {
.map_alloc = ringbuf_map_alloc,
.map_free = ringbuf_map_free,
.map_mmap = ringbuf_map_mmap,
.map_poll = ringbuf_map_poll,
.map_lookup_elem = ringbuf_map_lookup_elem,
.map_update_elem = ringbuf_map_update_elem,
.map_delete_elem = ringbuf_map_delete_elem,
.map_get_next_key = ringbuf_map_get_next_key,
};
/* Given pointer to ring buffer record metadata and struct bpf_ringbuf itself,
* calculate offset from record metadata to ring buffer in pages, rounded
* down. This page offset is stored as part of record metadata and allows to
* restore struct bpf_ringbuf * from record pointer. This page offset is
* stored at offset 4 of record metadata header.
*/
static size_t bpf_ringbuf_rec_pg_off(struct bpf_ringbuf *rb,
struct bpf_ringbuf_hdr *hdr)
{
return ((void *)hdr - (void *)rb) >> PAGE_SHIFT;
}
/* Given pointer to ring buffer record header, restore pointer to struct
* bpf_ringbuf itself by using page offset stored at offset 4
*/
static struct bpf_ringbuf *
bpf_ringbuf_restore_from_rec(struct bpf_ringbuf_hdr *hdr)
{
unsigned long addr = (unsigned long)(void *)hdr;
unsigned long off = (unsigned long)hdr->pg_off << PAGE_SHIFT;
return (void*)((addr & PAGE_MASK) - off);
}
static void *__bpf_ringbuf_reserve(struct bpf_ringbuf *rb, u64 size)
{
unsigned long cons_pos, prod_pos, new_prod_pos, flags;
u32 len, pg_off;
struct bpf_ringbuf_hdr *hdr;
if (unlikely(size > RINGBUF_MAX_RECORD_SZ))
return NULL;
len = round_up(size + BPF_RINGBUF_HDR_SZ, 8);
cons_pos = smp_load_acquire(&rb->consumer_pos);
if (in_nmi()) {
if (!spin_trylock_irqsave(&rb->spinlock, flags))
return NULL;
} else {
spin_lock_irqsave(&rb->spinlock, flags);
}
prod_pos = rb->producer_pos;
new_prod_pos = prod_pos + len;
/* check for out of ringbuf space by ensuring producer position
* doesn't advance more than (ringbuf_size - 1) ahead
*/
if (new_prod_pos - cons_pos > rb->mask) {
spin_unlock_irqrestore(&rb->spinlock, flags);
return NULL;
}
hdr = (void *)rb->data + (prod_pos & rb->mask);
pg_off = bpf_ringbuf_rec_pg_off(rb, hdr);
hdr->len = size | BPF_RINGBUF_BUSY_BIT;
hdr->pg_off = pg_off;
/* pairs with consumer's smp_load_acquire() */
smp_store_release(&rb->producer_pos, new_prod_pos);
spin_unlock_irqrestore(&rb->spinlock, flags);
return (void *)hdr + BPF_RINGBUF_HDR_SZ;
}
BPF_CALL_3(bpf_ringbuf_reserve, struct bpf_map *, map, u64, size, u64, flags)
{
struct bpf_ringbuf_map *rb_map;
if (unlikely(flags))
return 0;
rb_map = container_of(map, struct bpf_ringbuf_map, map);
return (unsigned long)__bpf_ringbuf_reserve(rb_map->rb, size);
}
const struct bpf_func_proto bpf_ringbuf_reserve_proto = {
.func = bpf_ringbuf_reserve,
.ret_type = RET_PTR_TO_ALLOC_MEM_OR_NULL,
.arg1_type = ARG_CONST_MAP_PTR,
.arg2_type = ARG_CONST_ALLOC_SIZE_OR_ZERO,
.arg3_type = ARG_ANYTHING,
};
static void bpf_ringbuf_commit(void *sample, u64 flags, bool discard)
{
unsigned long rec_pos, cons_pos;
struct bpf_ringbuf_hdr *hdr;
struct bpf_ringbuf *rb;
u32 new_len;
hdr = sample - BPF_RINGBUF_HDR_SZ;
rb = bpf_ringbuf_restore_from_rec(hdr);
new_len = hdr->len ^ BPF_RINGBUF_BUSY_BIT;
if (discard)
new_len |= BPF_RINGBUF_DISCARD_BIT;
/* update record header with correct final size prefix */
xchg(&hdr->len, new_len);
/* if consumer caught up and is waiting for our record, notify about
* new data availability
*/
rec_pos = (void *)hdr - (void *)rb->data;
cons_pos = smp_load_acquire(&rb->consumer_pos) & rb->mask;
if (flags & BPF_RB_FORCE_WAKEUP)
irq_work_queue(&rb->work);
else if (cons_pos == rec_pos && !(flags & BPF_RB_NO_WAKEUP))
irq_work_queue(&rb->work);
}
BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
{
bpf_ringbuf_commit(sample, flags, false /* discard */);
return 0;
}
const struct bpf_func_proto bpf_ringbuf_submit_proto = {
.func = bpf_ringbuf_submit,
.ret_type = RET_VOID,
.arg1_type = ARG_PTR_TO_ALLOC_MEM,
.arg2_type = ARG_ANYTHING,
};
BPF_CALL_2(bpf_ringbuf_discard, void *, sample, u64, flags)
{
bpf_ringbuf_commit(sample, flags, true /* discard */);
return 0;
}
const struct bpf_func_proto bpf_ringbuf_discard_proto = {
.func = bpf_ringbuf_discard,
.ret_type = RET_VOID,
.arg1_type = ARG_PTR_TO_ALLOC_MEM,
.arg2_type = ARG_ANYTHING,
};
BPF_CALL_4(bpf_ringbuf_output, struct bpf_map *, map, void *, data, u64, size,
u64, flags)
{
struct bpf_ringbuf_map *rb_map;
void *rec;
if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
return -EINVAL;
rb_map = container_of(map, struct bpf_ringbuf_map, map);
rec = __bpf_ringbuf_reserve(rb_map->rb, size);
if (!rec)
return -EAGAIN;
memcpy(rec, data, size);
bpf_ringbuf_commit(rec, flags, false /* discard */);
return 0;
}
const struct bpf_func_proto bpf_ringbuf_output_proto = {
.func = bpf_ringbuf_output,
.ret_type = RET_INTEGER,
.arg1_type = ARG_CONST_MAP_PTR,
.arg2_type = ARG_PTR_TO_MEM,
.arg3_type = ARG_CONST_SIZE_OR_ZERO,
.arg4_type = ARG_ANYTHING,
};
BPF_CALL_2(bpf_ringbuf_query, struct bpf_map *, map, u64, flags)
{
struct bpf_ringbuf *rb;
rb = container_of(map, struct bpf_ringbuf_map, map)->rb;
switch (flags) {
case BPF_RB_AVAIL_DATA:
return ringbuf_avail_data_sz(rb);
case BPF_RB_RING_SIZE:
return rb->mask + 1;
case BPF_RB_CONS_POS:
return smp_load_acquire(&rb->consumer_pos);
case BPF_RB_PROD_POS:
return smp_load_acquire(&rb->producer_pos);
default:
return 0;
}
}
const struct bpf_func_proto bpf_ringbuf_query_proto = {
.func = bpf_ringbuf_query,
.ret_type = RET_INTEGER,
.arg1_type = ARG_CONST_MAP_PTR,
.arg2_type = ARG_ANYTHING,
};