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, 65 insertions, 0 deletions

diff --git a/rust/syn/span.rs b/rust/syn/span.rs
new file mode 100644
index 000000000..e6d55b3cc
--- /dev/null
+++ b/rust/syn/span.rs
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use proc_macro2::extra::DelimSpan;
+use proc_macro2::{Delimiter, Group, Span, TokenStream};
+
+#[doc(hidden)]
+pub trait IntoSpans<S> {
+    fn into_spans(self) -> S;
+}
+
+impl IntoSpans<Span> for Span {
+    fn into_spans(self) -> Span {
+        self
+    }
+}
+
+impl IntoSpans<[Span; 1]> for Span {
+    fn into_spans(self) -> [Span; 1] {
+        [self]
+    }
+}
+
+impl IntoSpans<[Span; 2]> for Span {
+    fn into_spans(self) -> [Span; 2] {
+        [self, self]
+    }
+}
+
+impl IntoSpans<[Span; 3]> for Span {
+    fn into_spans(self) -> [Span; 3] {
+        [self, self, self]
+    }
+}
+
+impl IntoSpans<[Span; 1]> for [Span; 1] {
+    fn into_spans(self) -> [Span; 1] {
+        self
+    }
+}
+
+impl IntoSpans<[Span; 2]> for [Span; 2] {
+    fn into_spans(self) -> [Span; 2] {
+        self
+    }
+}
+
+impl IntoSpans<[Span; 3]> for [Span; 3] {
+    fn into_spans(self) -> [Span; 3] {
+        self
+    }
+}
+
+impl IntoSpans<DelimSpan> for Span {
+    fn into_spans(self) -> DelimSpan {
+        let mut group = Group::new(Delimiter::None, TokenStream::new());
+        group.set_span(self);
+        group.delim_span()
+    }
+}
+
+impl IntoSpans<DelimSpan> for DelimSpan {
+    fn into_spans(self) -> DelimSpan {
+        self
+    }
+}