linux/kernel/bpf/memalloc.c
Hou Tao c31b38cb94 bpf: Check whether or not node is NULL before free it in free_bulk
llnode could be NULL if there are new allocations after the checking of
c-free_cnt > c->high_watermark in bpf_mem_refill() and before the
calling of __llist_del_first() in free_bulk (e.g. a PREEMPT_RT kernel
or allocation in NMI context). And it will incur oops as shown below:

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 #PF: supervisor write access in kernel mode
 #PF: error_code(0x0002) - not-present page
 PGD 0 P4D 0
 Oops: 0002 [#1] PREEMPT_RT SMP
 CPU: 39 PID: 373 Comm: irq_work/39 Tainted: G        W          6.0.0-rc6-rt9+ #1
 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
 RIP: 0010:bpf_mem_refill+0x66/0x130
 ......
 Call Trace:
  <TASK>
  irq_work_single+0x24/0x60
  irq_work_run_list+0x24/0x30
  run_irq_workd+0x18/0x20
  smpboot_thread_fn+0x13f/0x2c0
  kthread+0x121/0x140
  ? kthread_complete_and_exit+0x20/0x20
  ret_from_fork+0x1f/0x30
  </TASK>

Simply fixing it by checking whether or not llnode is NULL in free_bulk().

Fixes: 8d5a8011b3 ("bpf: Batch call_rcu callbacks instead of SLAB_TYPESAFE_BY_RCU.")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20220919144811.3570825-1-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2022-09-20 08:06:27 -07:00

636 lines
17 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
#include <linux/mm.h>
#include <linux/llist.h>
#include <linux/bpf.h>
#include <linux/irq_work.h>
#include <linux/bpf_mem_alloc.h>
#include <linux/memcontrol.h>
#include <asm/local.h>
/* Any context (including NMI) BPF specific memory allocator.
*
* Tracing BPF programs can attach to kprobe and fentry. Hence they
* run in unknown context where calling plain kmalloc() might not be safe.
*
* Front-end kmalloc() with per-cpu per-bucket cache of free elements.
* Refill this cache asynchronously from irq_work.
*
* CPU_0 buckets
* 16 32 64 96 128 196 256 512 1024 2048 4096
* ...
* CPU_N buckets
* 16 32 64 96 128 196 256 512 1024 2048 4096
*
* The buckets are prefilled at the start.
* BPF programs always run with migration disabled.
* It's safe to allocate from cache of the current cpu with irqs disabled.
* Free-ing is always done into bucket of the current cpu as well.
* irq_work trims extra free elements from buckets with kfree
* and refills them with kmalloc, so global kmalloc logic takes care
* of freeing objects allocated by one cpu and freed on another.
*
* Every allocated objected is padded with extra 8 bytes that contains
* struct llist_node.
*/
#define LLIST_NODE_SZ sizeof(struct llist_node)
/* similar to kmalloc, but sizeof == 8 bucket is gone */
static u8 size_index[24] __ro_after_init = {
3, /* 8 */
3, /* 16 */
4, /* 24 */
4, /* 32 */
5, /* 40 */
5, /* 48 */
5, /* 56 */
5, /* 64 */
1, /* 72 */
1, /* 80 */
1, /* 88 */
1, /* 96 */
6, /* 104 */
6, /* 112 */
6, /* 120 */
6, /* 128 */
2, /* 136 */
2, /* 144 */
2, /* 152 */
2, /* 160 */
2, /* 168 */
2, /* 176 */
2, /* 184 */
2 /* 192 */
};
static int bpf_mem_cache_idx(size_t size)
{
if (!size || size > 4096)
return -1;
if (size <= 192)
return size_index[(size - 1) / 8] - 1;
return fls(size - 1) - 1;
}
#define NUM_CACHES 11
struct bpf_mem_cache {
/* per-cpu list of free objects of size 'unit_size'.
* All accesses are done with interrupts disabled and 'active' counter
* protection with __llist_add() and __llist_del_first().
*/
struct llist_head free_llist;
local_t active;
/* Operations on the free_list from unit_alloc/unit_free/bpf_mem_refill
* are sequenced by per-cpu 'active' counter. But unit_free() cannot
* fail. When 'active' is busy the unit_free() will add an object to
* free_llist_extra.
*/
struct llist_head free_llist_extra;
struct irq_work refill_work;
struct obj_cgroup *objcg;
int unit_size;
/* count of objects in free_llist */
int free_cnt;
int low_watermark, high_watermark, batch;
int percpu_size;
struct rcu_head rcu;
struct llist_head free_by_rcu;
struct llist_head waiting_for_gp;
atomic_t call_rcu_in_progress;
};
struct bpf_mem_caches {
struct bpf_mem_cache cache[NUM_CACHES];
};
static struct llist_node notrace *__llist_del_first(struct llist_head *head)
{
struct llist_node *entry, *next;
entry = head->first;
if (!entry)
return NULL;
next = entry->next;
head->first = next;
return entry;
}
static void *__alloc(struct bpf_mem_cache *c, int node)
{
/* Allocate, but don't deplete atomic reserves that typical
* GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
* will allocate from the current numa node which is what we
* want here.
*/
gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
if (c->percpu_size) {
void **obj = kmalloc_node(c->percpu_size, flags, node);
void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
if (!obj || !pptr) {
free_percpu(pptr);
kfree(obj);
return NULL;
}
obj[1] = pptr;
return obj;
}
return kmalloc_node(c->unit_size, flags, node);
}
static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
{
#ifdef CONFIG_MEMCG_KMEM
if (c->objcg)
return get_mem_cgroup_from_objcg(c->objcg);
#endif
#ifdef CONFIG_MEMCG
return root_mem_cgroup;
#else
return NULL;
#endif
}
/* Mostly runs from irq_work except __init phase. */
static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
{
struct mem_cgroup *memcg = NULL, *old_memcg;
unsigned long flags;
void *obj;
int i;
memcg = get_memcg(c);
old_memcg = set_active_memcg(memcg);
for (i = 0; i < cnt; i++) {
obj = __alloc(c, node);
if (!obj)
break;
if (IS_ENABLED(CONFIG_PREEMPT_RT))
/* In RT irq_work runs in per-cpu kthread, so disable
* interrupts to avoid preemption and interrupts and
* reduce the chance of bpf prog executing on this cpu
* when active counter is busy.
*/
local_irq_save(flags);
/* alloc_bulk runs from irq_work which will not preempt a bpf
* program that does unit_alloc/unit_free since IRQs are
* disabled there. There is no race to increment 'active'
* counter. It protects free_llist from corruption in case NMI
* bpf prog preempted this loop.
*/
WARN_ON_ONCE(local_inc_return(&c->active) != 1);
__llist_add(obj, &c->free_llist);
c->free_cnt++;
local_dec(&c->active);
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_restore(flags);
}
set_active_memcg(old_memcg);
mem_cgroup_put(memcg);
}
static void free_one(struct bpf_mem_cache *c, void *obj)
{
if (c->percpu_size) {
free_percpu(((void **)obj)[1]);
kfree(obj);
return;
}
kfree(obj);
}
static void __free_rcu(struct rcu_head *head)
{
struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
struct llist_node *pos, *t;
llist_for_each_safe(pos, t, llnode)
free_one(c, pos);
atomic_set(&c->call_rcu_in_progress, 0);
}
static void __free_rcu_tasks_trace(struct rcu_head *head)
{
struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
call_rcu(&c->rcu, __free_rcu);
}
static void enque_to_free(struct bpf_mem_cache *c, void *obj)
{
struct llist_node *llnode = obj;
/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
* Nothing races to add to free_by_rcu list.
*/
__llist_add(llnode, &c->free_by_rcu);
}
static void do_call_rcu(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
if (atomic_xchg(&c->call_rcu_in_progress, 1))
return;
WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
/* There is no concurrent __llist_add(waiting_for_gp) access.
* It doesn't race with llist_del_all either.
* But there could be two concurrent llist_del_all(waiting_for_gp):
* from __free_rcu() and from drain_mem_cache().
*/
__llist_add(llnode, &c->waiting_for_gp);
/* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
* Then use call_rcu() to wait for normal progs to finish
* and finally do free_one() on each element.
*/
call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace);
}
static void free_bulk(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
unsigned long flags;
int cnt;
do {
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_save(flags);
WARN_ON_ONCE(local_inc_return(&c->active) != 1);
llnode = __llist_del_first(&c->free_llist);
if (llnode)
cnt = --c->free_cnt;
else
cnt = 0;
local_dec(&c->active);
if (IS_ENABLED(CONFIG_PREEMPT_RT))
local_irq_restore(flags);
if (llnode)
enque_to_free(c, llnode);
} while (cnt > (c->high_watermark + c->low_watermark) / 2);
/* and drain free_llist_extra */
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
enque_to_free(c, llnode);
do_call_rcu(c);
}
static void bpf_mem_refill(struct irq_work *work)
{
struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
int cnt;
/* Racy access to free_cnt. It doesn't need to be 100% accurate */
cnt = c->free_cnt;
if (cnt < c->low_watermark)
/* irq_work runs on this cpu and kmalloc will allocate
* from the current numa node which is what we want here.
*/
alloc_bulk(c, c->batch, NUMA_NO_NODE);
else if (cnt > c->high_watermark)
free_bulk(c);
}
static void notrace irq_work_raise(struct bpf_mem_cache *c)
{
irq_work_queue(&c->refill_work);
}
/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
* the freelist cache will be elem_size * 64 (or less) on each cpu.
*
* For bpf programs that don't have statically known allocation sizes and
* assuming (low_mark + high_mark) / 2 as an average number of elements per
* bucket and all buckets are used the total amount of memory in freelists
* on each cpu will be:
* 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
* == ~ 116 Kbyte using below heuristic.
* Initialized, but unused bpf allocator (not bpf map specific one) will
* consume ~ 11 Kbyte per cpu.
* Typical case will be between 11K and 116K closer to 11K.
* bpf progs can and should share bpf_mem_cache when possible.
*/
static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
{
init_irq_work(&c->refill_work, bpf_mem_refill);
if (c->unit_size <= 256) {
c->low_watermark = 32;
c->high_watermark = 96;
} else {
/* When page_size == 4k, order-0 cache will have low_mark == 2
* and high_mark == 6 with batch alloc of 3 individual pages at
* a time.
* 8k allocs and above low == 1, high == 3, batch == 1.
*/
c->low_watermark = max(32 * 256 / c->unit_size, 1);
c->high_watermark = max(96 * 256 / c->unit_size, 3);
}
c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
/* To avoid consuming memory assume that 1st run of bpf
* prog won't be doing more than 4 map_update_elem from
* irq disabled region
*/
alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu));
}
/* When size != 0 bpf_mem_cache for each cpu.
* This is typical bpf hash map use case when all elements have equal size.
*
* When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
* kmalloc/kfree. Max allocation size is 4096 in this case.
* This is bpf_dynptr and bpf_kptr use case.
*/
int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
{
static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
struct bpf_mem_caches *cc, __percpu *pcc;
struct bpf_mem_cache *c, __percpu *pc;
struct obj_cgroup *objcg = NULL;
int cpu, i, unit_size, percpu_size = 0;
if (size) {
pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
if (!pc)
return -ENOMEM;
if (percpu)
/* room for llist_node and per-cpu pointer */
percpu_size = LLIST_NODE_SZ + sizeof(void *);
else
size += LLIST_NODE_SZ; /* room for llist_node */
unit_size = size;
#ifdef CONFIG_MEMCG_KMEM
objcg = get_obj_cgroup_from_current();
#endif
for_each_possible_cpu(cpu) {
c = per_cpu_ptr(pc, cpu);
c->unit_size = unit_size;
c->objcg = objcg;
c->percpu_size = percpu_size;
prefill_mem_cache(c, cpu);
}
ma->cache = pc;
return 0;
}
/* size == 0 && percpu is an invalid combination */
if (WARN_ON_ONCE(percpu))
return -EINVAL;
pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
if (!pcc)
return -ENOMEM;
#ifdef CONFIG_MEMCG_KMEM
objcg = get_obj_cgroup_from_current();
#endif
for_each_possible_cpu(cpu) {
cc = per_cpu_ptr(pcc, cpu);
for (i = 0; i < NUM_CACHES; i++) {
c = &cc->cache[i];
c->unit_size = sizes[i];
c->objcg = objcg;
prefill_mem_cache(c, cpu);
}
}
ma->caches = pcc;
return 0;
}
static void drain_mem_cache(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
/* No progs are using this bpf_mem_cache, but htab_map_free() called
* bpf_mem_cache_free() for all remaining elements and they can be in
* free_by_rcu or in waiting_for_gp lists, so drain those lists now.
*/
llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist))
free_one(c, llnode);
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
free_one(c, llnode);
}
static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
{
free_percpu(ma->cache);
free_percpu(ma->caches);
ma->cache = NULL;
ma->caches = NULL;
}
static void free_mem_alloc(struct bpf_mem_alloc *ma)
{
/* waiting_for_gp lists was drained, but __free_rcu might
* still execute. Wait for it now before we freeing percpu caches.
*/
rcu_barrier_tasks_trace();
rcu_barrier();
free_mem_alloc_no_barrier(ma);
}
static void free_mem_alloc_deferred(struct work_struct *work)
{
struct bpf_mem_alloc *ma = container_of(work, struct bpf_mem_alloc, work);
free_mem_alloc(ma);
kfree(ma);
}
static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
{
struct bpf_mem_alloc *copy;
if (!rcu_in_progress) {
/* Fast path. No callbacks are pending, hence no need to do
* rcu_barrier-s.
*/
free_mem_alloc_no_barrier(ma);
return;
}
copy = kmalloc(sizeof(*ma), GFP_KERNEL);
if (!copy) {
/* Slow path with inline barrier-s */
free_mem_alloc(ma);
return;
}
/* Defer barriers into worker to let the rest of map memory to be freed */
copy->cache = ma->cache;
ma->cache = NULL;
copy->caches = ma->caches;
ma->caches = NULL;
INIT_WORK(&copy->work, free_mem_alloc_deferred);
queue_work(system_unbound_wq, &copy->work);
}
void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
{
struct bpf_mem_caches *cc;
struct bpf_mem_cache *c;
int cpu, i, rcu_in_progress;
if (ma->cache) {
rcu_in_progress = 0;
for_each_possible_cpu(cpu) {
c = per_cpu_ptr(ma->cache, cpu);
drain_mem_cache(c);
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
/* objcg is the same across cpus */
if (c->objcg)
obj_cgroup_put(c->objcg);
destroy_mem_alloc(ma, rcu_in_progress);
}
if (ma->caches) {
rcu_in_progress = 0;
for_each_possible_cpu(cpu) {
cc = per_cpu_ptr(ma->caches, cpu);
for (i = 0; i < NUM_CACHES; i++) {
c = &cc->cache[i];
drain_mem_cache(c);
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
}
if (c->objcg)
obj_cgroup_put(c->objcg);
destroy_mem_alloc(ma, rcu_in_progress);
}
}
/* notrace is necessary here and in other functions to make sure
* bpf programs cannot attach to them and cause llist corruptions.
*/
static void notrace *unit_alloc(struct bpf_mem_cache *c)
{
struct llist_node *llnode = NULL;
unsigned long flags;
int cnt = 0;
/* Disable irqs to prevent the following race for majority of prog types:
* prog_A
* bpf_mem_alloc
* preemption or irq -> prog_B
* bpf_mem_alloc
*
* but prog_B could be a perf_event NMI prog.
* Use per-cpu 'active' counter to order free_list access between
* unit_alloc/unit_free/bpf_mem_refill.
*/
local_irq_save(flags);
if (local_inc_return(&c->active) == 1) {
llnode = __llist_del_first(&c->free_llist);
if (llnode)
cnt = --c->free_cnt;
}
local_dec(&c->active);
local_irq_restore(flags);
WARN_ON(cnt < 0);
if (cnt < c->low_watermark)
irq_work_raise(c);
return llnode;
}
/* Though 'ptr' object could have been allocated on a different cpu
* add it to the free_llist of the current cpu.
* Let kfree() logic deal with it when it's later called from irq_work.
*/
static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
{
struct llist_node *llnode = ptr - LLIST_NODE_SZ;
unsigned long flags;
int cnt = 0;
BUILD_BUG_ON(LLIST_NODE_SZ > 8);
local_irq_save(flags);
if (local_inc_return(&c->active) == 1) {
__llist_add(llnode, &c->free_llist);
cnt = ++c->free_cnt;
} else {
/* unit_free() cannot fail. Therefore add an object to atomic
* llist. free_bulk() will drain it. Though free_llist_extra is
* a per-cpu list we have to use atomic llist_add here, since
* it also can be interrupted by bpf nmi prog that does another
* unit_free() into the same free_llist_extra.
*/
llist_add(llnode, &c->free_llist_extra);
}
local_dec(&c->active);
local_irq_restore(flags);
if (cnt > c->high_watermark)
/* free few objects from current cpu into global kmalloc pool */
irq_work_raise(c);
}
/* Called from BPF program or from sys_bpf syscall.
* In both cases migration is disabled.
*/
void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
{
int idx;
void *ret;
if (!size)
return ZERO_SIZE_PTR;
idx = bpf_mem_cache_idx(size + LLIST_NODE_SZ);
if (idx < 0)
return NULL;
ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
return !ret ? NULL : ret + LLIST_NODE_SZ;
}
void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
{
int idx;
if (!ptr)
return;
idx = bpf_mem_cache_idx(ksize(ptr - LLIST_NODE_SZ));
if (idx < 0)
return;
unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}
void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
{
void *ret;
ret = unit_alloc(this_cpu_ptr(ma->cache));
return !ret ? NULL : ret + LLIST_NODE_SZ;
}
void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
{
if (!ptr)
return;
unit_free(this_cpu_ptr(ma->cache), ptr);
}