netdev - [bpf-next PATCH v2 4/7] bpf: test_progs, add test to catch retval refine error handling

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Message-ID: <158560423908.10843.11783152347709008373.stgit@john-Precision-5820-Tower>
Date:   Mon, 30 Mar 2020 14:37:19 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     ecree@...arflare.com, yhs@...com, alexei.starovoitov@...il.com,
        daniel@...earbox.net
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        john.fastabend@...il.com
Subject: [bpf-next PATCH v2 4/7] bpf: test_progs,
 add test to catch retval refine error handling

Before this series the verifier would clamp return bounds of
bpf_get_stack() to [0, X] and this led the verifier to believe
that a JMP_JSLT 0 would be false and so would prune that path.

The result is anything hidden behind that JSLT would be unverified.
Add a test to catch this case by hiding an goto pc-1 behind the
check which will cause an infinite loop if not rejected.

Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 .../selftests/bpf/prog_tests/get_stack_raw_tp.c    |    5 ++++
 .../selftests/bpf/progs/test_get_stack_rawtp_err.c |   26 ++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/test_get_stack_rawtp_err.c

diff --git a/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c b/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
index eba9a97..9257222 100644
--- a/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
+++ b/tools/testing/selftests/bpf/prog_tests/get_stack_raw_tp.c
@@ -82,6 +82,7 @@ static void get_stack_print_output(void *ctx, int cpu, void *data, __u32 size)
 void test_get_stack_raw_tp(void)
 {
 	const char *file = "./test_get_stack_rawtp.o";
+	const char *file_err = "./test_get_stack_rawtp_err.o";
 	const char *prog_name = "raw_tracepoint/sys_enter";
 	int i, err, prog_fd, exp_cnt = MAX_CNT_RAWTP;
 	struct perf_buffer_opts pb_opts = {};
@@ -93,6 +94,10 @@ void test_get_stack_raw_tp(void)
 	struct bpf_map *map;
 	cpu_set_t cpu_set;
 
+	err = bpf_prog_load(file_err, BPF_PROG_TYPE_RAW_TRACEPOINT, &obj, &prog_fd);
+	if (CHECK(err >= 0, "prog_load raw tp", "err %d errno %d\n", err, errno))
+		return;
+
 	err = bpf_prog_load(file, BPF_PROG_TYPE_RAW_TRACEPOINT, &obj, &prog_fd);
 	if (CHECK(err, "prog_load raw tp", "err %d errno %d\n", err, errno))
 		return;
diff --git a/tools/testing/selftests/bpf/progs/test_get_stack_rawtp_err.c b/tools/testing/selftests/bpf/progs/test_get_stack_rawtp_err.c
new file mode 100644
index 0000000..8941a41
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_get_stack_rawtp_err.c
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+
+#define MAX_STACK_RAWTP 10
+
+SEC("raw_tracepoint/sys_enter")
+int bpf_prog2(void *ctx)
+{
+	__u64 stack[MAX_STACK_RAWTP];
+	int error;
+
+	/* set all the flags which should return -EINVAL */
+	error = bpf_get_stack(ctx, stack, 0, -1);
+	if (error < 0)
+		goto loop;
+
+	return error;
+loop:
+	while (1) {
+		error++;
+	}
+}
+
+char _license[] SEC("license") = "GPL";