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, 35 insertions, 0 deletions

diff --git a/rust/syn/verbatim.rs b/rust/syn/verbatim.rs
new file mode 100644
index 000000000..97bc08f70
--- /dev/null
+++ b/rust/syn/verbatim.rs
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use crate::parse::ParseStream;
+use proc_macro2::{Delimiter, TokenStream};
+use std::cmp::Ordering;
+use std::iter;
+
+pub(crate) fn between<'a>(begin: ParseStream<'a>, end: ParseStream<'a>) -> TokenStream {
+    let end = end.cursor();
+    let mut cursor = begin.cursor();
+    assert!(crate::buffer::same_buffer(end, cursor));
+
+    let mut tokens = TokenStream::new();
+    while cursor != end {
+        let (tt, next) = cursor.token_tree().unwrap();
+
+        if crate::buffer::cmp_assuming_same_buffer(end, next) == Ordering::Less {
+            // A syntax node can cross the boundary of a None-delimited group
+            // due to such groups being transparent to the parser in most cases.
+            // Any time this occurs the group is known to be semantically
+            // irrelevant. https://github.com/dtolnay/syn/issues/1235
+            if let Some((inside, _span, after)) = cursor.group(Delimiter::None) {
+                assert!(next == after);
+                cursor = inside;
+                continue;
+            } else {
+                panic!("verbatim end must not be inside a delimited group");
+            }
+        }
+
+        tokens.extend(iter::once(tt));
+        cursor = next;
+    }
+    tokens
+}