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, 117 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_debug.c b/drivers/virtio/virtio_debug.c
new file mode 100644
index 000000000..ccf1955a1
--- /dev/null
+++ b/drivers/virtio/virtio_debug.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <linux/debugfs.h>
+
+static struct dentry *virtio_debugfs_dir;
+
+static int virtio_debug_device_features_show(struct seq_file *s, void *data)
+{
+	u64 device_features[VIRTIO_FEATURES_U64S];
+	struct virtio_device *dev = s->private;
+	unsigned int i;
+
+	virtio_get_features(dev, device_features);
+	for (i = 0; i < VIRTIO_FEATURES_BITS; i++) {
+		if (virtio_features_test_bit(device_features, i))
+			seq_printf(s, "%u\n", i);
+	}
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(virtio_debug_device_features);
+
+static int virtio_debug_filter_features_show(struct seq_file *s, void *data)
+{
+	struct virtio_device *dev = s->private;
+	unsigned int i;
+
+	for (i = 0; i < VIRTIO_FEATURES_BITS; i++) {
+		if (virtio_features_test_bit(dev->debugfs_filter_features, i))
+			seq_printf(s, "%u\n", i);
+	}
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(virtio_debug_filter_features);
+
+static int virtio_debug_filter_features_clear(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val == 1)
+		virtio_features_zero(dev->debugfs_filter_features);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_features_clear_fops, NULL,
+			 virtio_debug_filter_features_clear, "%llu\n");
+
+static int virtio_debug_filter_feature_add(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val >= VIRTIO_FEATURES_BITS)
+		return -EINVAL;
+
+	virtio_features_set_bit(dev->debugfs_filter_features, val);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_feature_add_fops, NULL,
+			 virtio_debug_filter_feature_add, "%llu\n");
+
+static int virtio_debug_filter_feature_del(void *data, u64 val)
+{
+	struct virtio_device *dev = data;
+
+	if (val >= VIRTIO_FEATURES_BITS)
+		return -EINVAL;
+
+	virtio_features_clear_bit(dev->debugfs_filter_features, val);
+	return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(virtio_debug_filter_feature_del_fops, NULL,
+			 virtio_debug_filter_feature_del, "%llu\n");
+
+void virtio_debug_device_init(struct virtio_device *dev)
+{
+	dev->debugfs_dir = debugfs_create_dir(dev_name(&dev->dev),
+					      virtio_debugfs_dir);
+	debugfs_create_file("device_features", 0400, dev->debugfs_dir, dev,
+			    &virtio_debug_device_features_fops);
+	debugfs_create_file("filter_features", 0400, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_features_fops);
+	debugfs_create_file("filter_features_clear", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_features_clear_fops);
+	debugfs_create_file("filter_feature_add", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_feature_add_fops);
+	debugfs_create_file("filter_feature_del", 0200, dev->debugfs_dir, dev,
+			    &virtio_debug_filter_feature_del_fops);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_init);
+
+void virtio_debug_device_filter_features(struct virtio_device *dev)
+{
+	virtio_features_andnot(dev->features_array, dev->features_array,
+			       dev->debugfs_filter_features);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_filter_features);
+
+void virtio_debug_device_exit(struct virtio_device *dev)
+{
+	debugfs_remove_recursive(dev->debugfs_dir);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_device_exit);
+
+void virtio_debug_init(void)
+{
+	virtio_debugfs_dir = debugfs_create_dir("virtio", NULL);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_init);
+
+void virtio_debug_exit(void)
+{
+	debugfs_remove_recursive(virtio_debugfs_dir);
+}
+EXPORT_SYMBOL_GPL(virtio_debug_exit);