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>

2 files changed, 81 insertions, 0 deletions

diff --git a/arch/m68k/tools/amiga/Makefile b/arch/m68k/tools/amiga/Makefile
new file mode 100644
index 000000000..e6425b367
--- /dev/null
+++ b/arch/m68k/tools/amiga/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0
+
+CC =		m68k-cbm-amigados-gcc
+CFLAGS =	-Wall -O2
+
+
+All:		dmesg
+
+
+dmesg:		dmesg.c
+		$(CC) $(CFLAGS) -o dmesg dmesg.c -noixemul
+
diff --git a/arch/m68k/tools/amiga/dmesg.c b/arch/m68k/tools/amiga/dmesg.c
new file mode 100644
index 000000000..f8005a7ef
--- /dev/null
+++ b/arch/m68k/tools/amiga/dmesg.c
@@ -0,0 +1,69 @@
+/*
+ *  linux/arch/m68k/tools/amiga/dmesg.c -- Retrieve the kernel messages stored
+ *					   in Chip RAM with the kernel command
+ *					   line option `debug=mem'.
+ *
+ *  © Copyright 1996 by Geert Uytterhoeven <geert@linux-m68k.org>
+ *
+ *
+ *  Usage:
+ *
+ *	dmesg
+ *	dmesg <CHIPMEM_END>
+ *
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+#define CHIPMEM_START	0x00000000
+#define CHIPMEM_END	0x00200000	/* overridden by argv[1] */
+
+#define SAVEKMSG_MAGIC1	0x53415645	/* 'SAVE' */
+#define SAVEKMSG_MAGIC2	0x4B4D5347	/* 'KMSG' */
+
+struct savekmsg {
+    u_long magic1;	/* SAVEKMSG_MAGIC1 */
+    u_long magic2;	/* SAVEKMSG_MAGIC2 */
+    u_long magicptr;	/* address of magic1 */
+    u_long size;
+    char data[];
+};
+
+
+int main(int argc, char *argv[])
+{
+    u_long start = CHIPMEM_START, end = CHIPMEM_END, p;
+    int found = 0;
+    struct savekmsg *m = NULL;
+
+    if (argc >= 2)
+	end = strtoul(argv[1], NULL, 0);
+    printf("Searching for SAVEKMSG magic...\n");
+    for (p = start; p <= end-sizeof(struct savekmsg); p += 4) {
+	m = (struct savekmsg *)p;
+	if ((m->magic1 == SAVEKMSG_MAGIC1) && (m->magic2 == SAVEKMSG_MAGIC2) &&
+	    (m->magicptr == p)) {
+	    found = 1;
+	    break;
+	}
+    }
+    if (!found)
+	printf("Not found\n");
+    else {
+	printf("Found %ld bytes at 0x%08lx\n", m->size, (u_long)&m->data);
+	puts(">>>>>>>>>>>>>>>>>>>>");
+	fflush(stdout);
+	write(1, &m->data, m->size);
+	fflush(stdout);
+	puts("<<<<<<<<<<<<<<<<<<<<");
+    }
+    return(0);
+}