selftests/bpf: Check that JMP32 pointer vs zero jumps are not predictedgrafted

Add jmp32_ptr_vs_zero_jne: the fall-through of the 32-bit compare, which
the verifier used to skip, contains an out of bounds map value access,
hence w/o the previous patch the program is accepted. See previous patch
for detailed description.

Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260904083325.2083493-6-eddyz87@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 60 insertions, 0 deletions

diff --git a/rust/syn/drops.rs b/rust/syn/drops.rs
new file mode 100644
index 000000000..2c4ae333d
--- /dev/null
+++ b/rust/syn/drops.rs
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use std::iter;
+use std::mem::ManuallyDrop;
+use std::ops::{Deref, DerefMut};
+use std::option;
+use std::slice;
+
+#[repr(transparent)]
+pub(crate) struct NoDrop<T: ?Sized>(ManuallyDrop<T>);
+
+impl<T> NoDrop<T> {
+    pub(crate) fn new(value: T) -> Self
+    where
+        T: TrivialDrop,
+    {
+        NoDrop(ManuallyDrop::new(value))
+    }
+}
+
+impl<T: ?Sized> Deref for NoDrop<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T: ?Sized> DerefMut for NoDrop<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+pub(crate) trait TrivialDrop {}
+
+impl<T> TrivialDrop for iter::Empty<T> {}
+impl<T> TrivialDrop for slice::Iter<'_, T> {}
+impl<T> TrivialDrop for slice::IterMut<'_, T> {}
+impl<T> TrivialDrop for option::IntoIter<&T> {}
+impl<T> TrivialDrop for option::IntoIter<&mut T> {}
+
+#[test]
+fn test_needs_drop() {
+    use std::mem::needs_drop;
+
+    struct NeedsDrop;
+
+    impl Drop for NeedsDrop {
+        fn drop(&mut self) {}
+    }
+
+    assert!(needs_drop::<NeedsDrop>());
+
+    // Test each of the types with a handwritten TrivialDrop impl above.
+    assert!(!needs_drop::<iter::Empty<NeedsDrop>>());
+    assert!(!needs_drop::<slice::Iter<NeedsDrop>>());
+    assert!(!needs_drop::<slice::IterMut<NeedsDrop>>());
+    assert!(!needs_drop::<option::IntoIter<&NeedsDrop>>());
+    assert!(!needs_drop::<option::IntoIter<&mut NeedsDrop>>());
+}