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, 41 insertions, 0 deletions

diff --git a/arch/powerpc/math-emu/fsel.c b/arch/powerpc/math-emu/fsel.c
new file mode 100644
index 000000000..b0d15e15a
--- /dev/null
+++ b/arch/powerpc/math-emu/fsel.c
@@ -0,0 +1,41 @@
+// 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>
+
+int
+fsel(u32 *frD, void *frA, u32 *frB, u32 *frC)
+{
+	FP_DECL_D(A);
+	FP_DECL_EX;
+
+#ifdef DEBUG
+	printk("%s: %p %p %p %p\n", __func__, frD, frA, frB, frC);
+#endif
+
+	FP_UNPACK_DP(A, frA);
+
+#ifdef DEBUG
+	printk("A: %ld %lu %lu %ld (%ld)\n", A_s, A_f1, A_f0, A_e, A_c);
+	printk("B: %08x %08x\n", frB[0], frB[1]);
+	printk("C: %08x %08x\n", frC[0], frC[1]);
+#endif
+
+	if (A_c == FP_CLS_NAN || (A_c != FP_CLS_ZERO && A_s)) {
+		frD[0] = frB[0];
+		frD[1] = frB[1];
+	} else {
+		frD[0] = frC[0];
+		frD[1] = frC[1];
+	}
+
+#ifdef DEBUG
+	printk("D: %08x.%08x\n", frD[0], frD[1]);
+#endif
+
+	return 0;
+}