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, 49 insertions, 0 deletions

diff --git a/arch/mips/sni/eisa.c b/arch/mips/sni/eisa.c
new file mode 100644
index 000000000..483a43d07
--- /dev/null
+++ b/arch/mips/sni/eisa.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Virtual EISA root driver.
+ * Acts as a placeholder if we don't have a proper EISA bridge.
+ *
+ * (C) 2003 Marc Zyngier <maz@wild-wind.fr.eu.org>
+ * modified for SNI usage by Thomas Bogendoerfer
+ */
+
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/eisa.h>
+#include <linux/init.h>
+
+/* The default EISA device parent (virtual root device).
+ * Now use a platform device, since that's the obvious choice. */
+
+static struct platform_device eisa_root_dev = {
+	.name = "eisa",
+	.id   = 0,
+};
+
+static struct eisa_root_device eisa_bus_root = {
+	.dev	       = &eisa_root_dev.dev,
+	.bus_base_addr = 0,
+	.res	       = &ioport_resource,
+	.slots	       = EISA_MAX_SLOTS,
+	.dma_mask      = 0xffffffff,
+	.force_probe   = 1,
+};
+
+int __init sni_eisa_root_init(void)
+{
+	int r;
+
+	r = platform_device_register(&eisa_root_dev);
+	if (!r)
+		return r;
+
+	dev_set_drvdata(&eisa_root_dev.dev, &eisa_bus_root);
+
+	if (eisa_root_register(&eisa_bus_root)) {
+		/* A real bridge may have been registered before
+		 * us. So quietly unregister. */
+		platform_device_unregister(&eisa_root_dev);
+		return -1;
+	}
+	return 0;
+}