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, 54 insertions, 0 deletions

diff --git a/drivers/firmware/google/memconsole.c b/drivers/firmware/google/memconsole.c
new file mode 100644
index 000000000..6138a1653
--- /dev/null
+++ b/drivers/firmware/google/memconsole.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * memconsole.c
+ *
+ * Architecture-independent parts of the memory based BIOS console.
+ *
+ * Copyright 2017 Google Inc.
+ */
+
+#include <linux/sysfs.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+
+#include "memconsole.h"
+
+static ssize_t memconsole_read(struct file *filp, struct kobject *kobp,
+			       const struct bin_attribute *bin_attr, char *buf,
+			       loff_t pos, size_t count)
+{
+	ssize_t (*memconsole_read_func)(char *, loff_t, size_t);
+
+	memconsole_read_func = bin_attr->private;
+	if (WARN_ON_ONCE(!memconsole_read_func))
+		return -EIO;
+
+	return memconsole_read_func(buf, pos, count);
+}
+
+static struct bin_attribute memconsole_bin_attr = {
+	.attr = {.name = "log", .mode = 0444},
+	.read = memconsole_read,
+};
+
+void memconsole_setup(ssize_t (*read_func)(char *, loff_t, size_t))
+{
+	memconsole_bin_attr.private = read_func;
+}
+EXPORT_SYMBOL(memconsole_setup);
+
+int memconsole_sysfs_init(void)
+{
+	return sysfs_create_bin_file(firmware_kobj, &memconsole_bin_attr);
+}
+EXPORT_SYMBOL(memconsole_sysfs_init);
+
+void memconsole_exit(void)
+{
+	sysfs_remove_bin_file(firmware_kobj, &memconsole_bin_attr);
+}
+EXPORT_SYMBOL(memconsole_exit);
+
+MODULE_AUTHOR("Google, Inc.");
+MODULE_DESCRIPTION("Architecture-independent parts of the memory based BIOS console");
+MODULE_LICENSE("GPL");