ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 228 insertions, 0 deletions

diff --git a/block/blk-stat.c b/block/blk-stat.c
new file mode 100644
index 000000000..de126e1ea
--- /dev/null
+++ b/block/blk-stat.c
@@ -0,0 +1,228 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Block stat tracking code
+ *
+ * Copyright (C) 2016 Jens Axboe
+ */
+#include <linux/kernel.h>
+#include <linux/rculist.h>
+
+#include "blk-stat.h"
+#include "blk-mq.h"
+#include "blk.h"
+
+struct blk_queue_stats {
+	struct list_head callbacks;
+	spinlock_t lock;
+	int accounting;
+};
+
+void blk_rq_stat_init(struct blk_rq_stat *stat)
+{
+	stat->min = -1ULL;
+	stat->max = stat->nr_samples = stat->mean = 0;
+	stat->batch = 0;
+}
+
+/* src is a per-cpu stat, mean isn't initialized */
+void blk_rq_stat_sum(struct blk_rq_stat *dst, struct blk_rq_stat *src)
+{
+	if (dst->nr_samples + src->nr_samples <= dst->nr_samples)
+		return;
+
+	dst->min = min(dst->min, src->min);
+	dst->max = max(dst->max, src->max);
+
+	dst->mean = div_u64(src->batch + dst->mean * dst->nr_samples,
+				dst->nr_samples + src->nr_samples);
+
+	dst->nr_samples += src->nr_samples;
+}
+
+void blk_rq_stat_add(struct blk_rq_stat *stat, u64 value)
+{
+	stat->min = min(stat->min, value);
+	stat->max = max(stat->max, value);
+	stat->batch += value;
+	stat->nr_samples++;
+}
+
+void blk_stat_add(struct request *rq, u64 now)
+{
+	struct request_queue *q = rq->q;
+	struct blk_stat_callback *cb;
+	struct blk_rq_stat *stat;
+	int bucket, cpu;
+	u64 value;
+
+	value = (now >= rq->io_start_time_ns) ? now - rq->io_start_time_ns : 0;
+
+	rcu_read_lock();
+	cpu = get_cpu();
+	list_for_each_entry_rcu(cb, &q->stats->callbacks, list) {
+		if (!blk_stat_is_active(cb))
+			continue;
+
+		bucket = cb->bucket_fn(rq);
+		if (bucket < 0)
+			continue;
+
+		stat = &per_cpu_ptr(cb->cpu_stat, cpu)[bucket];
+		blk_rq_stat_add(stat, value);
+	}
+	put_cpu();
+	rcu_read_unlock();
+}
+
+static void blk_stat_timer_fn(struct timer_list *t)
+{
+	struct blk_stat_callback *cb = timer_container_of(cb, t, timer);
+	unsigned int bucket;
+	int cpu;
+
+	for (bucket = 0; bucket < cb->buckets; bucket++)
+		blk_rq_stat_init(&cb->stat[bucket]);
+
+	for_each_online_cpu(cpu) {
+		struct blk_rq_stat *cpu_stat;
+
+		cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu);
+		for (bucket = 0; bucket < cb->buckets; bucket++) {
+			blk_rq_stat_sum(&cb->stat[bucket], &cpu_stat[bucket]);
+			blk_rq_stat_init(&cpu_stat[bucket]);
+		}
+	}
+
+	cb->timer_fn(cb);
+}
+
+struct blk_stat_callback *
+blk_stat_alloc_callback(void (*timer_fn)(struct blk_stat_callback *),
+			int (*bucket_fn)(const struct request *),
+			unsigned int buckets, void *data)
+{
+	struct blk_stat_callback *cb;
+
+	cb = kmalloc_obj(*cb);
+	if (!cb)
+		return NULL;
+
+	cb->stat = kmalloc_objs(struct blk_rq_stat, buckets);
+	if (!cb->stat) {
+		kfree(cb);
+		return NULL;
+	}
+	cb->cpu_stat = __alloc_percpu(buckets * sizeof(struct blk_rq_stat),
+				      __alignof__(struct blk_rq_stat));
+	if (!cb->cpu_stat) {
+		kfree(cb->stat);
+		kfree(cb);
+		return NULL;
+	}
+
+	cb->timer_fn = timer_fn;
+	cb->bucket_fn = bucket_fn;
+	cb->data = data;
+	cb->buckets = buckets;
+	timer_setup(&cb->timer, blk_stat_timer_fn, 0);
+
+	return cb;
+}
+
+void blk_stat_add_callback(struct request_queue *q,
+			   struct blk_stat_callback *cb)
+{
+	unsigned int bucket;
+	unsigned long flags;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		struct blk_rq_stat *cpu_stat;
+
+		cpu_stat = per_cpu_ptr(cb->cpu_stat, cpu);
+		for (bucket = 0; bucket < cb->buckets; bucket++)
+			blk_rq_stat_init(&cpu_stat[bucket]);
+	}
+
+	spin_lock_irqsave(&q->stats->lock, flags);
+	list_add_tail_rcu(&cb->list, &q->stats->callbacks);
+	blk_queue_flag_set(QUEUE_FLAG_STATS, q);
+	spin_unlock_irqrestore(&q->stats->lock, flags);
+}
+
+void blk_stat_remove_callback(struct request_queue *q,
+			      struct blk_stat_callback *cb)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->stats->lock, flags);
+	list_del_rcu(&cb->list);
+	if (list_empty(&q->stats->callbacks) && !q->stats->accounting)
+		blk_queue_flag_clear(QUEUE_FLAG_STATS, q);
+	spin_unlock_irqrestore(&q->stats->lock, flags);
+
+	timer_delete_sync(&cb->timer);
+}
+
+static void blk_stat_free_callback_rcu(struct rcu_head *head)
+{
+	struct blk_stat_callback *cb;
+
+	cb = container_of(head, struct blk_stat_callback, rcu);
+	free_percpu(cb->cpu_stat);
+	kfree(cb->stat);
+	kfree(cb);
+}
+
+void blk_stat_free_callback(struct blk_stat_callback *cb)
+{
+	if (cb)
+		call_rcu(&cb->rcu, blk_stat_free_callback_rcu);
+}
+
+void blk_stat_disable_accounting(struct request_queue *q)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->stats->lock, flags);
+	if (!--q->stats->accounting && list_empty(&q->stats->callbacks))
+		blk_queue_flag_clear(QUEUE_FLAG_STATS, q);
+	spin_unlock_irqrestore(&q->stats->lock, flags);
+}
+EXPORT_SYMBOL_GPL(blk_stat_disable_accounting);
+
+void blk_stat_enable_accounting(struct request_queue *q)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&q->stats->lock, flags);
+	if (!q->stats->accounting++ && list_empty(&q->stats->callbacks))
+		blk_queue_flag_set(QUEUE_FLAG_STATS, q);
+	spin_unlock_irqrestore(&q->stats->lock, flags);
+}
+EXPORT_SYMBOL_GPL(blk_stat_enable_accounting);
+
+struct blk_queue_stats *blk_alloc_queue_stats(void)
+{
+	struct blk_queue_stats *stats;
+
+	stats = kmalloc_obj(*stats);
+	if (!stats)
+		return NULL;
+
+	INIT_LIST_HEAD(&stats->callbacks);
+	spin_lock_init(&stats->lock);
+	stats->accounting = 0;
+
+	return stats;
+}
+
+void blk_free_queue_stats(struct blk_queue_stats *stats)
+{
+	if (!stats)
+		return;
+
+	WARN_ON(!list_empty(&stats->callbacks));
+
+	kfree(stats);
+}