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, 183 insertions, 0 deletions

diff --git a/samples/bpf/tracex3_user.c b/samples/bpf/tracex3_user.c
new file mode 100644
index 000000000..1002eb032
--- /dev/null
+++ b/samples/bpf/tracex3_user.c
@@ -0,0 +1,183 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2013-2015 PLUMgrid, http://plumgrid.com
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <unistd.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+#include "bpf_util.h"
+
+#define SLOTS 100
+
+static void clear_stats(int fd)
+{
+	unsigned int nr_cpus = bpf_num_possible_cpus();
+	__u64 values[nr_cpus];
+	__u32 key;
+
+	memset(values, 0, sizeof(values));
+	for (key = 0; key < SLOTS; key++)
+		bpf_map_update_elem(fd, &key, values, BPF_ANY);
+}
+
+const char *color[] = {
+	"\033[48;5;255m",
+	"\033[48;5;252m",
+	"\033[48;5;250m",
+	"\033[48;5;248m",
+	"\033[48;5;246m",
+	"\033[48;5;244m",
+	"\033[48;5;242m",
+	"\033[48;5;240m",
+	"\033[48;5;238m",
+	"\033[48;5;236m",
+	"\033[48;5;234m",
+	"\033[48;5;232m",
+};
+const int num_colors = ARRAY_SIZE(color);
+
+const char nocolor[] = "\033[00m";
+
+const char *sym[] = {
+	" ",
+	" ",
+	".",
+	".",
+	"*",
+	"*",
+	"o",
+	"o",
+	"O",
+	"O",
+	"#",
+	"#",
+};
+
+bool full_range = false;
+bool text_only = false;
+
+static void print_banner(void)
+{
+	if (full_range)
+		printf("|1ns     |10ns     |100ns    |1us      |10us     |100us"
+		       "    |1ms      |10ms     |100ms    |1s       |10s\n");
+	else
+		printf("|1us      |10us     |100us    |1ms      |10ms     "
+		       "|100ms    |1s       |10s\n");
+}
+
+static void print_hist(int fd)
+{
+	unsigned int nr_cpus = bpf_num_possible_cpus();
+	__u64 total_events = 0;
+	long values[nr_cpus];
+	__u64 max_cnt = 0;
+	__u64 cnt[SLOTS];
+	__u64 value;
+	__u32 key;
+	int i;
+
+	for (key = 0; key < SLOTS; key++) {
+		bpf_map_lookup_elem(fd, &key, values);
+		value = 0;
+		for (i = 0; i < nr_cpus; i++)
+			value += values[i];
+		cnt[key] = value;
+		total_events += value;
+		if (value > max_cnt)
+			max_cnt = value;
+	}
+	clear_stats(fd);
+	for (key = full_range ? 0 : 29; key < SLOTS; key++) {
+		int c = num_colors * cnt[key] / (max_cnt + 1);
+
+		if (text_only)
+			printf("%s", sym[c]);
+		else
+			printf("%s %s", color[c], nocolor);
+	}
+	printf(" # %lld\n", total_events);
+}
+
+int main(int ac, char **argv)
+{
+	struct bpf_link *links[2];
+	struct bpf_program *prog;
+	struct bpf_object *obj;
+	char filename[256];
+	int map_fd, i, j = 0;
+
+	for (i = 1; i < ac; i++) {
+		if (strcmp(argv[i], "-a") == 0) {
+			full_range = true;
+		} else if (strcmp(argv[i], "-t") == 0) {
+			text_only = true;
+		} else if (strcmp(argv[i], "-h") == 0) {
+			printf("Usage:\n"
+			       "  -a display wider latency range\n"
+			       "  -t text only\n");
+			return 1;
+		}
+	}
+
+	snprintf(filename, sizeof(filename), "%s.bpf.o", argv[0]);
+	obj = bpf_object__open_file(filename, NULL);
+	if (libbpf_get_error(obj)) {
+		fprintf(stderr, "ERROR: opening BPF object file failed\n");
+		return 0;
+	}
+
+	/* load BPF program */
+	if (bpf_object__load(obj)) {
+		fprintf(stderr, "ERROR: loading BPF object file failed\n");
+		goto cleanup;
+	}
+
+	map_fd = bpf_object__find_map_fd_by_name(obj, "lat_map");
+	if (map_fd < 0) {
+		fprintf(stderr, "ERROR: finding a map in obj file failed\n");
+		goto cleanup;
+	}
+
+	bpf_object__for_each_program(prog, obj) {
+		links[j] = bpf_program__attach(prog);
+		if (libbpf_get_error(links[j])) {
+			fprintf(stderr, "ERROR: bpf_program__attach failed\n");
+			links[j] = NULL;
+			goto cleanup;
+		}
+		j++;
+	}
+
+	printf("  heatmap of IO latency\n");
+	if (text_only)
+		printf("  %s", sym[num_colors - 1]);
+	else
+		printf("  %s %s", color[num_colors - 1], nocolor);
+	printf(" - many events with this latency\n");
+
+	if (text_only)
+		printf("  %s", sym[0]);
+	else
+		printf("  %s %s", color[0], nocolor);
+	printf(" - few events\n");
+
+	for (i = 0; ; i++) {
+		if (i % 20 == 0)
+			print_banner();
+		print_hist(map_fd);
+		sleep(2);
+	}
+
+cleanup:
+	for (j--; j >= 0; j--)
+		bpf_link__destroy(links[j]);
+
+	bpf_object__close(obj);
+	return 0;
+}