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, 63 insertions, 0 deletions

diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
new file mode 100644
index 000000000..892e69ab4
--- /dev/null
+++ b/init/do_mounts_initrd.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/unistd.h>
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/initrd.h>
+
+#include "do_mounts.h"
+
+unsigned long initrd_start, initrd_end;
+int initrd_below_start_ok;
+static int __initdata mount_initrd = 1;
+
+phys_addr_t phys_initrd_start __initdata;
+unsigned long phys_initrd_size __initdata;
+
+static int __init no_initrd(char *str)
+{
+	pr_warn("noinitrd option is deprecated and will be removed soon\n");
+	mount_initrd = 0;
+	return 1;
+}
+
+__setup("noinitrd", no_initrd);
+
+static int __init early_initrdmem(char *p)
+{
+	phys_addr_t start;
+	unsigned long size;
+	char *endp;
+
+	start = memparse(p, &endp);
+	if (*endp == ',') {
+		size = memparse(endp + 1, NULL);
+
+		phys_initrd_start = start;
+		phys_initrd_size = size;
+	}
+	return 0;
+}
+early_param("initrdmem", early_initrdmem);
+
+static int __init early_initrd(char *p)
+{
+	return early_initrdmem(p);
+}
+early_param("initrd", early_initrd);
+
+void __init initrd_load(void)
+{
+	if (mount_initrd) {
+		create_dev("/dev/ram", Root_RAM0);
+		/*
+		 * Load the initrd data into /dev/ram0.
+		 */
+		if (rd_load_image()) {
+			pr_warn("using deprecated initrd support, will be removed in January 2027; "
+				"use initramfs instead or (as a last resort) /sys/firmware/initrd; "
+				"see section \"Workaround\" in "
+				"https://lore.kernel.org/lkml/20251010094047.3111495-1-safinaskar@gmail.com\n");
+		}
+	}
+	init_unlink("/initrd.image");
+}