[PATCH bpf-next 5/5] selftests/bpf: Test log_true_size with an error from blinding

[Qiliang Yuan]

A prog of one function gets its constants blinded when its runtime is
selected, which can log an error.

No test checks that log_true_size counts such an error.

Load a prog whose jump goes over 11000 constants with bpf_jit_harden=2.
Blinding pushes the jump out of its 16-bit range, and the message must
be in the log and in log_true_size.

Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Closes: https://lore.kernel.org/bpf/DMKHZS5B5CNO.186F6YH1T6YU4@xxxxxxxxx/
Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 .../selftests/bpf/prog_tests/blinding_log.c        | 59 ++++++++++++++++++++++
 1 file changed, 59 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/blinding_log.c b/tools/testing/selftests/bpf/prog_tests/blinding_log.c
new file mode 100644
index 0000000000000..658a8494dae5b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/blinding_log.c
@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/* The verifier log of a prog whose constants are blinded */
+
+#include <test_progs.h>
+#include <linux/filter.h>
+#include "sysctl_helpers.h"
+
+#define NR_CONSTS 11000
+#define LOG_SIZE 65536
+
+/*
+ * A prog of one function gets its constants blinded when its runtime is
+ * selected. Each 'r0 += 1' becomes 3 insns, which pushes the jump over them
+ * out of its 16-bit range. Serial, because it sets bpf_jit_harden.
+ */
+void serial_test_blinding_log(void)
+{
+	const char *harden = "/proc/sys/net/core/bpf_jit_harden";
+	LIBBPF_OPTS(bpf_prog_load_opts, opts);
+	struct bpf_insn *insns;
+	char old[16] = {}, *log;
+	int i, cnt = 0, fd;
+
+	if (!is_jit_enabled()) {
+		printf("%s:SKIP:JIT is disabled\n", __func__);
+		test__skip();
+		return;
+	}
+
+	insns = calloc(NR_CONSTS + 3, sizeof(*insns));
+	log = calloc(1, LOG_SIZE);
+	if (!ASSERT_OK_PTR(insns, "insns") || !ASSERT_OK_PTR(log, "log"))
+		goto out;
+
+	insns[cnt++] = BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32);
+	insns[cnt++] = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, NR_CONSTS);
+	for (i = 0; i < NR_CONSTS; i++)
+		insns[cnt++] = BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 1);
+	insns[cnt++] = BPF_EXIT_INSN();
+
+	opts.log_buf = log;
+	opts.log_size = LOG_SIZE;
+	/* log stats only: level 1 logs each insn, which wraps the buffer */
+	opts.log_level = 4;
+	if (sysctl_set_or_fail(harden, old, "2"))
+		goto out;
+	fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, cnt, &opts);
+	sysctl_set_or_fail(harden, NULL, old);
+	/* don't mind whether the interpreter takes the prog or the load fails */
+	if (fd >= 0)
+		close(fd);
+
+	/* expect the message about the jump in the log and in log_true_size */
+	ASSERT_HAS_SUBSTR(log, "cannot be patched due to 16-bit range", "log");
+	ASSERT_EQ(opts.log_true_size, strlen(log) + 1, "log_true_size");
+out:
+	free(insns);
+	free(log);
+}

-- 
2.43.0