linux/kernel/bpf/ringbuf.c
Joanne Koong bc34dee65a bpf: Dynptr support for ring buffers
Currently, our only way of writing dynamically-sized data into a ring
buffer is through bpf_ringbuf_output but this incurs an extra memcpy
cost. bpf_ringbuf_reserve + bpf_ringbuf_commit avoids this extra
memcpy, but it can only safely support reservation sizes that are
statically known since the verifier cannot guarantee that the bpf
program won’t access memory outside the reserved space.

The bpf_dynptr abstraction allows for dynamically-sized ring buffer
reservations without the extra memcpy.

There are 3 new APIs:

long bpf_ringbuf_reserve_dynptr(void *ringbuf, u32 size, u64 flags, struct bpf_dynptr *ptr);
void bpf_ringbuf_submit_dynptr(struct bpf_dynptr *ptr, u64 flags);
void bpf_ringbuf_discard_dynptr(struct bpf_dynptr *ptr, u64 flags);

These closely follow the functionalities of the original ringbuf APIs.
For example, all ringbuffer dynptrs that have been reserved must be
either submitted or discarded before the program exits.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/bpf/20220523210712.3641569-4-joannelkoong@gmail.com
2022-05-23 14:31:28 -07:00

556 lines
14 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 <linux/kmemleak.h>
#include <uapi/linux/btf.h>
#include <linux/btf_ids.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_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_ACCOUNT | __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);
pages = bpf_map_area_alloc(array_size, 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_MAP | VM_USERMAP, PAGE_KERNEL);
if (rb) {
kmemleak_not_leak(pages);
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 NULL;
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;
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 | __GFP_ACCOUNT);
if (!rb_map)
return ERR_PTR(-ENOMEM);
bpf_map_init_from_attr(&rb_map->map, attr);
rb_map->rb = bpf_ringbuf_alloc(attr->max_entries, rb_map->map.numa_node);
if (!rb_map->rb) {
kfree(rb_map);
return ERR_PTR(-ENOMEM);
}
return &rb_map->map;
}
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;
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 int ringbuf_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
{
struct bpf_ringbuf_map *rb_map;
rb_map = container_of(map, struct bpf_ringbuf_map, map);
if (vma->vm_flags & VM_WRITE) {
/* allow writable mapping for the consumer_pos only */
if (vma->vm_pgoff != 0 || vma->vm_end - vma->vm_start != PAGE_SIZE)
return -EPERM;
} else {
vma->vm_flags &= ~VM_MAYWRITE;
}
/* remap_vmalloc_range() checks size and offset constraints */
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;
}
BTF_ID_LIST_SINGLE(ringbuf_map_btf_ids, struct, bpf_ringbuf_map)
const struct bpf_map_ops ringbuf_map_ops = {
.map_meta_equal = bpf_map_meta_equal,
.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,
.map_btf_id = &ringbuf_map_btf_ids[0],
};
/* 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);
if (len > rb->mask + 1)
return NULL;
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 | OBJ_RELEASE,
.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 | OBJ_RELEASE,
.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 | MEM_RDONLY,
.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,
};
BPF_CALL_4(bpf_ringbuf_reserve_dynptr, struct bpf_map *, map, u32, size, u64, flags,
struct bpf_dynptr_kern *, ptr)
{
struct bpf_ringbuf_map *rb_map;
void *sample;
int err;
if (unlikely(flags)) {
bpf_dynptr_set_null(ptr);
return -EINVAL;
}
err = bpf_dynptr_check_size(size);
if (err) {
bpf_dynptr_set_null(ptr);
return err;
}
rb_map = container_of(map, struct bpf_ringbuf_map, map);
sample = __bpf_ringbuf_reserve(rb_map->rb, size);
if (!sample) {
bpf_dynptr_set_null(ptr);
return -EINVAL;
}
bpf_dynptr_init(ptr, sample, BPF_DYNPTR_TYPE_RINGBUF, 0, size);
return 0;
}
const struct bpf_func_proto bpf_ringbuf_reserve_dynptr_proto = {
.func = bpf_ringbuf_reserve_dynptr,
.ret_type = RET_INTEGER,
.arg1_type = ARG_CONST_MAP_PTR,
.arg2_type = ARG_ANYTHING,
.arg3_type = ARG_ANYTHING,
.arg4_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | MEM_UNINIT,
};
BPF_CALL_2(bpf_ringbuf_submit_dynptr, struct bpf_dynptr_kern *, ptr, u64, flags)
{
if (!ptr->data)
return 0;
bpf_ringbuf_commit(ptr->data, flags, false /* discard */);
bpf_dynptr_set_null(ptr);
return 0;
}
const struct bpf_func_proto bpf_ringbuf_submit_dynptr_proto = {
.func = bpf_ringbuf_submit_dynptr,
.ret_type = RET_VOID,
.arg1_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | OBJ_RELEASE,
.arg2_type = ARG_ANYTHING,
};
BPF_CALL_2(bpf_ringbuf_discard_dynptr, struct bpf_dynptr_kern *, ptr, u64, flags)
{
if (!ptr->data)
return 0;
bpf_ringbuf_commit(ptr->data, flags, true /* discard */);
bpf_dynptr_set_null(ptr);
return 0;
}
const struct bpf_func_proto bpf_ringbuf_discard_dynptr_proto = {
.func = bpf_ringbuf_discard_dynptr,
.ret_type = RET_VOID,
.arg1_type = ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_RINGBUF | OBJ_RELEASE,
.arg2_type = ARG_ANYTHING,
};