// SPDX-License-Identifier: GPL-2.0
/*
* KASAN quarantine.
*
* Author: Alexander Potapenko <[email protected]>
* Copyright (C) 2016 Google, Inc.
*
* Based on code by Dmitry Chernenkov.
*/
#define pr_fmt(fmt) "kasan: " fmt
#include <linux/gfp.h>
#include <linux/hash.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/printk.h>
#include <linux/shrinker.h>
#include <linux/slab.h>
#include <linux/srcu.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/cpuhotplug.h>
#include "../slab.h"
#include "kasan.h"
/* Data structure and operations for quarantine queues. */
/*
* Each queue is a single-linked list, which also stores the total size of
* objects inside of it.
*/
struct qlist_head {
struct qlist_node *head;
struct qlist_node *tail;
size_t bytes;
bool offline;
};
#define QLIST_INIT { NULL, NULL, 0 }
static bool qlist_empty(struct qlist_head *q)
{
return !q->head;
}
static void qlist_init(struct qlist_head *q)
{
q->head = q->tail = NULL;
q->bytes = 0;
}
static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
size_t size)
{
if (unlikely(qlist_empty(q)))
q->head = qlink;
else
q->tail->next = qlink;
q->tail = qlink;
qlink->next = NULL;
q->bytes += size;
}
static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
{
if (unlikely(qlist_empty(from)))
return;
if (qlist_empty(to)) {
*to = *from;
qlist_init(from);
return;
}
to->tail->next = from->head;
to->tail = from->tail;
to->bytes += from->bytes;
qlist_init(from);
}
#define QUARANTINE_PERCPU_SIZE (1 << 20)
#define QUARANTINE_BATCHES \
(1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)
/*
* The object quarantine consists of per-cpu queues and a global queue,
* guarded by quarantine_lock.
*/
static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
/* Round-robin FIFO array of batches. */
static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
static int quarantine_head;
static int quarantine_tail;
/* Total size of all objects in global_quarantine across all batches. */
static unsigned long quarantine_size;
static DEFINE_RAW_SPINLOCK(quarantine_lock);
DEFINE_STATIC_SRCU(remove_cache_srcu);
struct cpu_shrink_qlist {
raw_spinlock_t lock;
struct qlist_head qlist;
};
static DEFINE_PER_CPU(struct cpu_shrink_qlist, shrink_qlist) = {
.lock = __RAW_SPIN_LOCK_UNLOCKED(shrink_qlist.lock),
};
/* Maximum size of the global queue. */
static unsigned long quarantine_max_size;
/*
* Target size of a batch in global_quarantine.
* Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
*/
static unsigned long quarantine_batch_size;
/*
* The fraction of physical memory the quarantine is allowed to occupy.
* Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
* the ratio low to avoid OOM.
*/
#define QUARANTINE_FRACTION 32
static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
{
return virt_to_slab(qlink)->slab_cache;
}
static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
{
struct kasan_free_meta *free_info =
container_of(qlink, struct kasan_free_meta,
quarantine_link);
return ((void *)free_info) - cache->kasan_info.free_meta_offset;
}
static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
{
void *object = qlink_to_object(qlink, cache);
struct kasan_free_meta *free_meta = kasan_get_free_meta(cache, object);
/*
* Note: Keep per-object metadata to allow KASAN print stack traces for
* use-after-free-before-realloc bugs.
*/
/*
* If init_on_free is enabled and KASAN's free metadata is stored in
* the object, zero the metadata. Otherwise, the object's memory will
* not be properly zeroed, as KASAN saves the metadata after the slab
* allocator zeroes the object.
*/
if (slab_want_init_on_free(cache) &&
cache->kasan_info.free_meta_offset == 0)
memzero_explicit(free_meta, sizeof(*free_meta));
___cache_free(cache, object, _THIS_IP_);
}
static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
{
struct qlist_node *qlink;
if (unlikely(qlist_empty(q)))
return;
qlink = q->head;
while (qlink) {
struct kmem_cache *obj_cache =
cache ? cache : qlink_to_cache(qlink);
struct qlist_node *next = qlink->next;
qlink_free(qlink, obj_cache);
qlink = next;
}
qlist_init(q);
}
bool kasan_quarantine_put(struct kmem_cache *cache, void *object)
{
unsigned long flags;
struct qlist_head *q;
struct qlist_head temp = QLIST_INIT;
struct kasan_free_meta *meta = kasan_get_free_meta(cache, object);
/*
* If there's no metadata for this object, don't put it into
* quarantine.
*/
if (!meta)
return false;
/*
* Note: irq must be disabled until after we move the batch to the
* global quarantine. Otherwise kasan_quarantine_remove_cache() can
* miss some objects belonging to the cache if they are in our local
* temp list. kasan_quarantine_remove_cache() executes on_each_cpu()
* at the beginning which ensures that it either sees the objects in
* per-cpu lists or in the global quarantine.
*/
local_irq_save(flags);
q = this_cpu_ptr(&cpu_quarantine);
if (q->offline) {
local_irq_restore(flags);
return false;
}
qlist_put(q, &meta->quarantine_link, cache->size);
if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) {
qlist_move_all(q, &temp);
raw_spin_lock(&quarantine_lock);
WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
if (global_quarantine[quarantine_tail].bytes >=
READ_ONCE(quarantine_batch_size)) {
int new_tail;
new_tail = quarantine_tail + 1;
if (new_tail == QUARANTINE_BATCHES)
new_tail = 0;
if (new_tail != quarantine_head)
quarantine_tail = new_tail;
}
raw_spin_unlock(&quarantine_lock);
}
local_irq_restore(flags);
return true;
}
void kasan_quarantine_reduce(void)
{
size_t total_size, new_quarantine_size, percpu_quarantines;
unsigned long flags;
int srcu_idx;
struct qlist_head to_free = QLIST_INIT;
if (likely(READ_ONCE(quarantine_size) <=
READ_ONCE(quarantine_max_size)))
return;
/*
* srcu critical section ensures that kasan_quarantine_remove_cache()
* will not miss objects belonging to the cache while they are in our
* local to_free list. srcu is chosen because (1) it gives us private
* grace period domain that does not interfere with anything else,
* and (2) it allows synchronize_srcu() to return without waiting
* if there are no pending read critical sections (which is the
* expected case).
*/
srcu_idx = srcu_read_lock(&remove_cache_srcu);
raw_spin_lock_irqsave(&quarantine_lock, flags);
/*
* Update quarantine size in case of hotplug. Allocate a fraction of
* the installed memory to quarantine minus per-cpu queue limits.
*/
total_size = (totalram_pages() << PAGE_SHIFT) /
QUARANTINE_FRACTION;
percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
new_quarantine_size = (total_size < percpu_quarantines) ?
0 : total_size - percpu_quarantines;
WRITE_ONCE(quarantine_max_size, new_quarantine_size);
/* Aim at consuming at most 1/2 of slots in quarantine. */
WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
2 * total_size / QUARANTINE_BATCHES));
if (likely(quarantine_size > quarantine_max_size)) {
qlist_move_all(&global_quarantine[quarantine_head], &to_free);
WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
quarantine_head++;
if (quarantine_head == QUARANTINE_BATCHES)
quarantine_head = 0;
}
raw_spin_unlock_irqrestore(&quarantine_lock, flags);
qlist_free_all(&to_free, NULL);
srcu_read_unlock(&remove_cache_srcu, srcu_idx);
}
static void qlist_move_cache(struct qlist_head *from,
struct qlist_head *to,
struct kmem_cache *cache)
{
struct qlist_node *curr;
if (unlikely(qlist_empty(from)))
return;
curr = from->head;
qlist_init(from);
while (curr) {
struct qlist_node *next = curr->next;
struct kmem_cache *obj_cache = qlink_to_cache(curr);
if (obj_cache == cache)
qlist_put(to, curr, obj_cache->size);
else
qlist_put(from, curr, obj_cache->size);
curr = next;
}
}
static void __per_cpu_remove_cache(struct qlist_head *q, void *arg)
{
struct kmem_cache *cache = arg;
unsigned long flags;
struct cpu_shrink_qlist *sq;
sq = this_cpu_ptr(&shrink_qlist);
raw_spin_lock_irqsave(&sq->lock, flags);
qlist_move_cache(q, &sq->qlist, cache);
raw_spin_unlock_irqrestore(&sq->lock, flags);
}
static void per_cpu_remove_cache(void *arg)
{
struct qlist_head *q;
q = this_cpu_ptr(&cpu_quarantine);
/*
* Ensure the ordering between the writing to q->offline and
* per_cpu_remove_cache. Prevent cpu_quarantine from being corrupted
* by interrupt.
*/
if (READ_ONCE(q->offline))
return;
__per_cpu_remove_cache(q, arg);
}
/* Free all quarantined objects belonging to cache. */
void kasan_quarantine_remove_cache(struct kmem_cache *cache)
{
unsigned long flags, i;
struct qlist_head to_free = QLIST_INIT;
int cpu;
struct cpu_shrink_qlist *sq;
/*
* Must be careful to not miss any objects that are being moved from
* per-cpu list to the global quarantine in kasan_quarantine_put(),
* nor objects being freed in kasan_quarantine_reduce(). on_each_cpu()
* achieves the first goal, while synchronize_srcu() achieves the
* second.
*/
on_each_cpu(per_cpu_remove_cache, cache, 1);
for_each_online_cpu(cpu) {
sq = per_cpu_ptr(&shrink_qlist, cpu);
raw_spin_lock_irqsave(&sq->lock, flags);
qlist_move_cache(&sq->qlist, &to_free, cache);
raw_spin_unlock_irqrestore(&sq->lock, flags);
}
qlist_free_all(&to_free, cache);
raw_spin_lock_irqsave(&quarantine_lock, flags);
for (i = 0; i < QUARANTINE_BATCHES; i++) {
if (qlist_empty(&global_quarantine[i]))
continue;
qlist_move_cache(&global_quarantine[i], &to_free, cache);
/* Scanning whole quarantine can take a while. */
raw_spin_unlock_irqrestore(&quarantine_lock, flags);
cond_resched();
raw_spin_lock_irqsave(&quarantine_lock, flags);
}
raw_spin_unlock_irqrestore(&quarantine_lock, flags);
qlist_free_all(&to_free, cache);
synchronize_srcu(&remove_cache_srcu);
}
static int kasan_cpu_online(unsigned int cpu)
{
this_cpu_ptr(&cpu_quarantine)->offline = false;
return 0;
}
static int kasan_cpu_offline(unsigned int cpu)
{
struct qlist_head *q;
q = this_cpu_ptr(&cpu_quarantine);
/* Ensure the ordering between the writing to q->offline and
* qlist_free_all. Otherwise, cpu_quarantine may be corrupted
* by interrupt.
*/
WRITE_ONCE(q->offline, true);
barrier();
qlist_free_all(q, NULL);
return 0;
}
static int __init kasan_cpu_quarantine_init(void)
{
int ret = 0;
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online",
kasan_cpu_online, kasan_cpu_offline);
if (ret < 0)
pr_err("cpu quarantine register failed [%d]\n", ret);
return ret;
}
late_initcall(kasan_cpu_quarantine_init);
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