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, 60 insertions, 0 deletions

diff --git a/rust/macros/helpers.rs b/rust/macros/helpers.rs
new file mode 100644
index 000000000..d18fbf4da
--- /dev/null
+++ b/rust/macros/helpers.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use syn::{
+    parse::{
+        Parse,
+        ParseStream, //
+    },
+    Attribute,
+    Error,
+    LitStr,
+    Result, //
+};
+
+/// A string literal that is required to have ASCII value only.
+pub(crate) struct AsciiLitStr(LitStr);
+
+impl Parse for AsciiLitStr {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
+        let s: LitStr = input.parse()?;
+        if !s.value().is_ascii() {
+            return Err(Error::new_spanned(s, "expected ASCII-only string literal"));
+        }
+        Ok(Self(s))
+    }
+}
+
+impl ToTokens for AsciiLitStr {
+    fn to_tokens(&self, ts: &mut TokenStream) {
+        self.0.to_tokens(ts);
+    }
+}
+
+impl AsciiLitStr {
+    pub(crate) fn value(&self) -> String {
+        self.0.value()
+    }
+}
+
+pub(crate) fn file() -> String {
+    #[cfg(not(CONFIG_RUSTC_HAS_SPAN_FILE))]
+    {
+        proc_macro::Span::call_site()
+            .source_file()
+            .path()
+            .to_string_lossy()
+            .into_owned()
+    }
+
+    #[cfg(CONFIG_RUSTC_HAS_SPAN_FILE)]
+    {
+        proc_macro::Span::call_site().file()
+    }
+}
+
+/// Obtain all `#[cfg]` attributes.
+pub(crate) fn gather_cfg_attrs(attr: &[Attribute]) -> impl Iterator<Item = &Attribute> + '_ {
+    attr.iter().filter(|a| a.path().is_ident("cfg"))
+}