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, 47 insertions, 0 deletions

diff --git a/arch/powerpc/math-emu/lfs.c b/arch/powerpc/math-emu/lfs.c
new file mode 100644
index 000000000..7fd3d0854
--- /dev/null
+++ b/arch/powerpc/math-emu/lfs.c
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+
+#include <asm/sfp-machine.h>
+#include <math-emu/soft-fp.h>
+#include <math-emu/double.h>
+#include <math-emu/single.h>
+
+int
+lfs(void *frD, void *ea)
+{
+	FP_DECL_D(R);
+	FP_DECL_S(A);
+	FP_DECL_EX;
+	float f;
+
+#ifdef DEBUG
+	printk("%s: D %p, ea %p\n", __func__, frD, ea);
+#endif
+
+	if (copy_from_user(&f, ea, sizeof(float)))
+		return -EFAULT;
+
+	FP_UNPACK_S(A, f);
+
+#ifdef DEBUG
+	printk("A: %ld %lu %ld (%ld) [%08lx]\n", A_s, A_f, A_e, A_c,
+	       *(unsigned long *)&f);
+#endif
+
+	FP_CONV(D, S, 2, 1, R, A);
+
+#ifdef DEBUG
+	printk("R: %ld %lu %lu %ld (%ld)\n", R_s, R_f1, R_f0, R_e, R_c);
+#endif
+
+	if (R_c == FP_CLS_NAN) {
+		R_e = _FP_EXPMAX_D;
+		_FP_PACK_RAW_2_P(D, frD, R);
+	} else {
+		__FP_PACK_D(frD, R);
+	}
+
+	return 0;
+}