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/x86/boot/mkcpustr.c b/arch/x86/boot/mkcpustr.c
new file mode 100644
index 000000000..22d730b22
--- /dev/null
+++ b/arch/x86/boot/mkcpustr.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* ----------------------------------------------------------------------- *
+ *
+ *   Copyright 2008 rPath, Inc. - All Rights Reserved
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * This is a host program to preprocess the CPU strings into a
+ * compact format suitable for the setup code.
+ */
+
+#include <stdio.h>
+
+#include "../include/asm/cpufeatures.h"
+#include "../include/asm/vmxfeatures.h"
+#include "../kernel/cpu/capflags.c"
+
+int main(void)
+{
+	int i, j;
+	const char *str;
+
+	printf("#include <asm/cpufeaturemasks.h>\n\n");
+	printf("static const char x86_cap_strs[] =\n");
+
+	for (i = 0; i < NCAPINTS; i++) {
+		for (j = 0; j < 32; j++) {
+			str = x86_cap_flags[i*32+j];
+
+			if (i == NCAPINTS-1 && j == 31) {
+				/* The last entry must be unconditional; this
+				   also consumes the compiler-added null
+				   character */
+				if (!str)
+					str = "";
+				printf("\t\"\\x%02x\\x%02x\"\"%s\"\n",
+				       i, j, str);
+			} else if (str) {
+				printf("#if REQUIRED_MASK%d & (1 << %d)\n"
+				       "\t\"\\x%02x\\x%02x\"\"%s\\0\"\n"
+				       "#endif\n",
+				       i, j, i, j, str);
+			}
+		}
+	}
+	printf("\t;\n");
+	return 0;
+}