selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 316 insertions, 0 deletions

diff --git a/fs/erofs/zutil.c b/fs/erofs/zutil.c
new file mode 100644
index 000000000..a0ce9226b
--- /dev/null
+++ b/fs/erofs/zutil.c
@@ -0,0 +1,316 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2018 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ * Copyright (C) 2024 Alibaba Cloud
+ */
+#include "internal.h"
+
+struct z_erofs_gbuf {
+	spinlock_t lock;
+	void *ptr;
+	struct page **pages;
+	unsigned int nrpages;
+};
+
+static struct z_erofs_gbuf *z_erofs_gbufpool, *z_erofs_rsvbuf;
+static unsigned int z_erofs_gbuf_count, z_erofs_gbuf_nrpages,
+		z_erofs_rsv_nrpages;
+
+module_param_named(global_buffers, z_erofs_gbuf_count, uint, 0444);
+module_param_named(reserved_pages, z_erofs_rsv_nrpages, uint, 0444);
+
+atomic_long_t erofs_global_shrink_cnt;	/* for all mounted instances */
+
+/* protects `erofs_sb_list_lock` and the mounted `erofs_sb_list` */
+static DEFINE_SPINLOCK(erofs_sb_list_lock);
+static LIST_HEAD(erofs_sb_list);
+static unsigned int shrinker_run_no;
+static struct shrinker *erofs_shrinker_info;
+
+static unsigned int z_erofs_gbuf_id(void)
+{
+	return raw_smp_processor_id() % z_erofs_gbuf_count;
+}
+
+void *z_erofs_get_gbuf(unsigned int requiredpages)
+	__acquires(gbuf->lock)
+{
+	struct z_erofs_gbuf *gbuf;
+
+	migrate_disable();
+	gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
+	spin_lock(&gbuf->lock);
+	/* check if the buffer is too small */
+	if (requiredpages > gbuf->nrpages) {
+		spin_unlock(&gbuf->lock);
+		migrate_enable();
+		/* (for sparse checker) pretend gbuf->lock is still taken */
+		__acquire(gbuf->lock);
+		return NULL;
+	}
+	return gbuf->ptr;
+}
+
+void z_erofs_put_gbuf(void *ptr) __releases(gbuf->lock)
+{
+	struct z_erofs_gbuf *gbuf;
+
+	gbuf = &z_erofs_gbufpool[z_erofs_gbuf_id()];
+	DBG_BUGON(gbuf->ptr != ptr);
+	spin_unlock(&gbuf->lock);
+	migrate_enable();
+}
+
+int z_erofs_gbuf_growsize(unsigned int nrpages)
+{
+	static DEFINE_MUTEX(gbuf_resize_mutex);
+	struct page **tmp_pages = NULL;
+	struct z_erofs_gbuf *gbuf;
+	void *ptr, *old_ptr;
+	int last, i, j;
+
+	mutex_lock(&gbuf_resize_mutex);
+	/* avoid shrinking gbufs, since no idea how many fses rely on */
+	if (nrpages <= z_erofs_gbuf_nrpages) {
+		mutex_unlock(&gbuf_resize_mutex);
+		return 0;
+	}
+
+	for (i = 0; i < z_erofs_gbuf_count; ++i) {
+		gbuf = &z_erofs_gbufpool[i];
+		tmp_pages = kzalloc_objs(*tmp_pages, nrpages);
+		if (!tmp_pages)
+			goto out;
+
+		for (j = 0; j < gbuf->nrpages; ++j)
+			tmp_pages[j] = gbuf->pages[j];
+		do {
+			last = j;
+			j = alloc_pages_bulk(GFP_KERNEL, nrpages,
+					     tmp_pages);
+			if (last == j)
+				goto out;
+		} while (j != nrpages);
+
+		ptr = vmap(tmp_pages, nrpages, VM_MAP, PAGE_KERNEL);
+		if (!ptr)
+			goto out;
+
+		spin_lock(&gbuf->lock);
+		kfree(gbuf->pages);
+		gbuf->pages = tmp_pages;
+		old_ptr = gbuf->ptr;
+		gbuf->ptr = ptr;
+		gbuf->nrpages = nrpages;
+		spin_unlock(&gbuf->lock);
+		if (old_ptr)
+			vunmap(old_ptr);
+	}
+	z_erofs_gbuf_nrpages = nrpages;
+out:
+	if (i < z_erofs_gbuf_count && tmp_pages) {
+		for (j = 0; j < nrpages; ++j)
+			if (tmp_pages[j] && (j >= gbuf->nrpages ||
+					     tmp_pages[j] != gbuf->pages[j]))
+				__free_page(tmp_pages[j]);
+		kfree(tmp_pages);
+	}
+	mutex_unlock(&gbuf_resize_mutex);
+	return i < z_erofs_gbuf_count ? -ENOMEM : 0;
+}
+
+int __init z_erofs_gbuf_init(void)
+{
+	unsigned int i, total = num_possible_cpus();
+
+	if (z_erofs_gbuf_count)
+		total = min(z_erofs_gbuf_count, total);
+	z_erofs_gbuf_count = total;
+
+	/* The last (special) global buffer is the reserved buffer */
+	total += !!z_erofs_rsv_nrpages;
+
+	z_erofs_gbufpool = kzalloc_objs(*z_erofs_gbufpool, total);
+	if (!z_erofs_gbufpool)
+		return -ENOMEM;
+
+	if (z_erofs_rsv_nrpages) {
+		z_erofs_rsvbuf = &z_erofs_gbufpool[total - 1];
+		z_erofs_rsvbuf->pages = kzalloc_objs(*z_erofs_rsvbuf->pages,
+						     z_erofs_rsv_nrpages);
+		if (!z_erofs_rsvbuf->pages) {
+			z_erofs_rsvbuf = NULL;
+			z_erofs_rsv_nrpages = 0;
+		}
+	}
+	for (i = 0; i < total; ++i)
+		spin_lock_init(&z_erofs_gbufpool[i].lock);
+	return 0;
+}
+
+void z_erofs_gbuf_exit(void)
+{
+	int i, j;
+
+	for (i = 0; i < z_erofs_gbuf_count + (!!z_erofs_rsvbuf); ++i) {
+		struct z_erofs_gbuf *gbuf = &z_erofs_gbufpool[i];
+
+		if (gbuf->ptr) {
+			vunmap(gbuf->ptr);
+			gbuf->ptr = NULL;
+		}
+
+		if (!gbuf->pages)
+			continue;
+
+		for (j = 0; j < gbuf->nrpages; ++j)
+			if (gbuf->pages[j])
+				put_page(gbuf->pages[j]);
+		kfree(gbuf->pages);
+		gbuf->pages = NULL;
+	}
+	kfree(z_erofs_gbufpool);
+}
+
+struct page *__erofs_allocpage(struct page **pagepool, gfp_t gfp, bool tryrsv)
+{
+	struct page *page = *pagepool;
+
+	if (page) {
+		*pagepool = (struct page *)page_private(page);
+	} else if (tryrsv && z_erofs_rsvbuf && z_erofs_rsvbuf->nrpages) {
+		spin_lock(&z_erofs_rsvbuf->lock);
+		if (z_erofs_rsvbuf->nrpages)
+			page = z_erofs_rsvbuf->pages[--z_erofs_rsvbuf->nrpages];
+		spin_unlock(&z_erofs_rsvbuf->lock);
+	}
+	if (!page)
+		page = alloc_page(gfp);
+	DBG_BUGON(page && page_ref_count(page) != 1);
+	return page;
+}
+
+void erofs_release_pages(struct page **pagepool)
+{
+	while (*pagepool) {
+		struct page *page = *pagepool;
+
+		*pagepool = (struct page *)page_private(page);
+		/* try to fill reserved global pool first */
+		if (z_erofs_rsvbuf && z_erofs_rsvbuf->nrpages <
+				z_erofs_rsv_nrpages) {
+			spin_lock(&z_erofs_rsvbuf->lock);
+			if (z_erofs_rsvbuf->nrpages < z_erofs_rsv_nrpages) {
+				z_erofs_rsvbuf->pages[z_erofs_rsvbuf->nrpages++]
+						= page;
+				spin_unlock(&z_erofs_rsvbuf->lock);
+				continue;
+			}
+			spin_unlock(&z_erofs_rsvbuf->lock);
+		}
+		put_page(page);
+	}
+}
+
+void erofs_shrinker_register(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+
+	mutex_init(&sbi->umount_mutex);
+
+	spin_lock(&erofs_sb_list_lock);
+	list_add(&sbi->list, &erofs_sb_list);
+	spin_unlock(&erofs_sb_list_lock);
+}
+
+void erofs_shrinker_unregister(struct super_block *sb)
+{
+	struct erofs_sb_info *const sbi = EROFS_SB(sb);
+
+	mutex_lock(&sbi->umount_mutex);
+	while (!xa_empty(&sbi->managed_pslots)) {
+		z_erofs_shrink_scan(sbi, ~0UL);
+		cond_resched();
+	}
+	spin_lock(&erofs_sb_list_lock);
+	list_del(&sbi->list);
+	spin_unlock(&erofs_sb_list_lock);
+	mutex_unlock(&sbi->umount_mutex);
+}
+
+static unsigned long erofs_shrink_count(struct shrinker *shrink,
+					struct shrink_control *sc)
+{
+	return atomic_long_read(&erofs_global_shrink_cnt) ?: SHRINK_EMPTY;
+}
+
+static unsigned long erofs_shrink_scan(struct shrinker *shrink,
+				       struct shrink_control *sc)
+{
+	struct erofs_sb_info *sbi;
+	struct list_head *p;
+
+	unsigned long nr = sc->nr_to_scan;
+	unsigned int run_no;
+	unsigned long freed = 0;
+
+	spin_lock(&erofs_sb_list_lock);
+	do {
+		run_no = ++shrinker_run_no;
+	} while (run_no == 0);
+
+	/* Iterate over all mounted superblocks and try to shrink them */
+	p = erofs_sb_list.next;
+	while (p != &erofs_sb_list) {
+		sbi = list_entry(p, struct erofs_sb_info, list);
+
+		/*
+		 * We move the ones we do to the end of the list, so we stop
+		 * when we see one we have already done.
+		 */
+		if (sbi->shrinker_run_no == run_no)
+			break;
+
+		if (!mutex_trylock(&sbi->umount_mutex)) {
+			p = p->next;
+			continue;
+		}
+
+		spin_unlock(&erofs_sb_list_lock);
+		sbi->shrinker_run_no = run_no;
+		freed += z_erofs_shrink_scan(sbi, nr - freed);
+		spin_lock(&erofs_sb_list_lock);
+		/* Get the next list element before we move this one */
+		p = p->next;
+
+		/*
+		 * Move this one to the end of the list to provide some
+		 * fairness.
+		 */
+		list_move_tail(&sbi->list, &erofs_sb_list);
+		mutex_unlock(&sbi->umount_mutex);
+
+		if (freed >= nr)
+			break;
+	}
+	spin_unlock(&erofs_sb_list_lock);
+	return freed;
+}
+
+int __init erofs_init_shrinker(void)
+{
+	erofs_shrinker_info = shrinker_alloc(0, "erofs-shrinker");
+	if (!erofs_shrinker_info)
+		return -ENOMEM;
+
+	erofs_shrinker_info->count_objects = erofs_shrink_count;
+	erofs_shrinker_info->scan_objects = erofs_shrink_scan;
+	shrinker_register(erofs_shrinker_info);
+	return 0;
+}
+
+void erofs_exit_shrinker(void)
+{
+	shrinker_free(erofs_shrinker_info);
+}