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, 86 insertions, 0 deletions

diff --git a/drivers/md/dm-verity-loadpin.c b/drivers/md/dm-verity-loadpin.c
new file mode 100644
index 000000000..9a64f575a
--- /dev/null
+++ b/drivers/md/dm-verity-loadpin.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/list.h>
+#include <linux/kernel.h>
+#include <linux/dm-verity-loadpin.h>
+
+#include "dm.h"
+#include "dm-core.h"
+#include "dm-verity.h"
+
+#define DM_MSG_PREFIX	"verity-loadpin"
+
+LIST_HEAD(dm_verity_loadpin_trusted_root_digests);
+
+static bool is_trusted_verity_target(struct dm_target *ti)
+{
+	int verity_mode;
+	u8 *root_digest;
+	unsigned int digest_size;
+	struct dm_verity_loadpin_trusted_root_digest *trd;
+	bool trusted = false;
+
+	if (!dm_is_verity_target(ti))
+		return false;
+
+	verity_mode = dm_verity_get_mode(ti);
+
+	if ((verity_mode != DM_VERITY_MODE_EIO) &&
+	    (verity_mode != DM_VERITY_MODE_RESTART) &&
+	    (verity_mode != DM_VERITY_MODE_PANIC))
+		return false;
+
+	if (dm_verity_get_root_digest(ti, &root_digest, &digest_size))
+		return false;
+
+	list_for_each_entry(trd, &dm_verity_loadpin_trusted_root_digests, node) {
+		if ((trd->len == digest_size) &&
+		    !memcmp(trd->data, root_digest, digest_size)) {
+			trusted = true;
+			break;
+		}
+	}
+
+	kfree(root_digest);
+
+	return trusted;
+}
+
+/*
+ * Determines whether the file system of a superblock is located on
+ * a verity device that is trusted by LoadPin.
+ */
+bool dm_verity_loadpin_is_bdev_trusted(struct block_device *bdev)
+{
+	struct mapped_device *md;
+	struct dm_table *table;
+	struct dm_target *ti;
+	int srcu_idx;
+	bool trusted = false;
+
+	if (bdev == NULL)
+		return false;
+
+	if (list_empty(&dm_verity_loadpin_trusted_root_digests))
+		return false;
+
+	md = dm_get_md(bdev->bd_dev);
+	if (!md)
+		return false;
+
+	table = dm_get_live_table(md, &srcu_idx);
+
+	if (!table || table->num_targets != 1)
+		goto out;
+
+	ti = dm_table_get_target(table, 0);
+
+	if (is_trusted_verity_target(ti))
+		trusted = true;
+
+out:
+	dm_put_live_table(md, srcu_idx);
+	dm_put(md);
+
+	return trusted;
+}