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, 100 insertions, 0 deletions

diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
new file mode 100644
index 000000000..0ca8715fe
--- /dev/null
+++ b/drivers/block/rnull/rnull.rs
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! This is a Rust implementation of the C null block driver.
+
+mod configfs;
+
+use configfs::IRQMode;
+use kernel::{
+    block::{
+        self,
+        mq::{
+            self,
+            gen_disk::{self, GenDisk},
+            Operations, TagSet,
+        },
+    },
+    prelude::*,
+    sync::{aref::ARef, Arc},
+};
+
+module! {
+    type: NullBlkModule,
+    name: "rnull_mod",
+    authors: ["Andreas Hindborg"],
+    description: "Rust implementation of the C null block driver",
+    license: "GPL v2",
+}
+
+#[pin_data]
+struct NullBlkModule {
+    #[pin]
+    configfs_subsystem: kernel::configfs::Subsystem<configfs::Config>,
+}
+
+impl kernel::InPlaceModule for NullBlkModule {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+        pr_info!("Rust null_blk loaded\n");
+
+        try_pin_init!(Self {
+            configfs_subsystem <- configfs::subsystem(),
+        })
+    }
+}
+
+struct NullBlkDevice;
+
+impl NullBlkDevice {
+    fn new(
+        name: &CStr,
+        block_size: u32,
+        rotational: bool,
+        capacity_mib: u64,
+        irq_mode: IRQMode,
+    ) -> Result<GenDisk<Self>> {
+        let tagset = Arc::pin_init(TagSet::new(1, 256, 1), GFP_KERNEL)?;
+
+        let queue_data = Box::new(QueueData { irq_mode }, GFP_KERNEL)?;
+
+        gen_disk::GenDiskBuilder::new()
+            .capacity_sectors(capacity_mib << (20 - block::SECTOR_SHIFT))
+            .logical_block_size(block_size)?
+            .physical_block_size(block_size)?
+            .rotational(rotational)
+            .build(fmt!("{}", name.to_str()?), tagset, queue_data)
+    }
+}
+
+struct QueueData {
+    irq_mode: IRQMode,
+}
+
+#[vtable]
+impl Operations for NullBlkDevice {
+    type QueueData = KBox<QueueData>;
+
+    #[inline(always)]
+    fn queue_rq(queue_data: &QueueData, rq: ARef<mq::Request<Self>>, _is_last: bool) -> Result {
+        match queue_data.irq_mode {
+            IRQMode::None => mq::Request::end_ok(rq)
+                .map_err(|_e| kernel::error::code::EIO)
+                // We take no refcounts on the request, so we expect to be able to
+                // end the request. The request reference must be unique at this
+                // point, and so `end_ok` cannot fail.
+                .expect("Fatal error - expected to be able to end request"),
+            IRQMode::Soft => mq::Request::complete(rq),
+        }
+        Ok(())
+    }
+
+    fn commit_rqs(_queue_data: &QueueData) {}
+
+    fn complete(rq: ARef<mq::Request<Self>>) {
+        mq::Request::end_ok(rq)
+            .map_err(|_e| kernel::error::code::EIO)
+            // We take no refcounts on the request, so we expect to be able to
+            // end the request. The request reference must be unique at this
+            // point, and so `end_ok` cannot fail.
+            .expect("Fatal error - expected to be able to end request");
+    }
+}