bpf: selftest: Ensure the return value of the bpf_per_cpu_ptr() must be checked

This patch tests all pointers returned by bpf_per_cpu_ptr() must be
tested for NULL first before it can be accessed.

This patch adds a subtest "null_check", so it moves the ".data..percpu"
existence check to the very beginning and before doing any subtest.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201019194225.1051596-1-kafai@fb.com

diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
index 28e26bd..b58b775 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
@@ -5,18 +5,17 @@
 #include <bpf/libbpf.h>
 #include <bpf/btf.h>
 #include "test_ksyms_btf.skel.h"
+#include "test_ksyms_btf_null_check.skel.h"
 
 static int duration;
 
-void test_ksyms_btf(void)
+static void test_basic(void)
 {
        __u64 runqueues_addr, bpf_prog_active_addr;
        __u32 this_rq_cpu;
        int this_bpf_prog_active;
        struct test_ksyms_btf *skel = NULL;
        struct test_ksyms_btf__data *data;
-       struct btf *btf;
-       int percpu_datasec;
        int err;
 
        err = kallsyms_find("runqueues", &runqueues_addr);
@@ -31,20 +30,6 @@ void test_ksyms_btf(void)
        if (CHECK(err == -ENOENT, "ksym_find", "symbol 'bpf_prog_active' not found\n"))
                return;
 
-       btf = libbpf_find_kernel_btf();
-       if (CHECK(IS_ERR(btf), "btf_exists", "failed to load kernel BTF: %ld\n",
-                 PTR_ERR(btf)))
-               return;
-
-       percpu_datasec = btf__find_by_name_kind(btf, ".data..percpu",
-                                               BTF_KIND_DATASEC);
-       if (percpu_datasec < 0) {
-               printf("%s:SKIP:no PERCPU DATASEC in kernel btf\n",
-                      __func__);
-               test__skip();
-               goto cleanup;
-       }
-
        skel = test_ksyms_btf__open_and_load();
        if (CHECK(!skel, "skel_open", "failed to open and load skeleton\n"))
                goto cleanup;
@@ -83,6 +68,42 @@ void test_ksyms_btf(void)
              data->out__bpf_prog_active);
 
 cleanup:
-       btf__free(btf);
        test_ksyms_btf__destroy(skel);
 }
+
+static void test_null_check(void)
+{
+       struct test_ksyms_btf_null_check *skel;
+
+       skel = test_ksyms_btf_null_check__open_and_load();
+       CHECK(skel, "skel_open", "unexpected load of a prog missing null check\n");
+
+       test_ksyms_btf_null_check__destroy(skel);
+}
+
+void test_ksyms_btf(void)
+{
+       int percpu_datasec;
+       struct btf *btf;
+
+       btf = libbpf_find_kernel_btf();
+       if (CHECK(IS_ERR(btf), "btf_exists", "failed to load kernel BTF: %ld\n",
+                 PTR_ERR(btf)))
+               return;
+
+       percpu_datasec = btf__find_by_name_kind(btf, ".data..percpu",
+                                               BTF_KIND_DATASEC);
+       btf__free(btf);
+       if (percpu_datasec < 0) {
+               printf("%s:SKIP:no PERCPU DATASEC in kernel btf\n",
+                      __func__);
+               test__skip();
+               return;
+       }
+
+       if (test__start_subtest("basic"))
+               test_basic();
+
+       if (test__start_subtest("null_check"))
+               test_null_check();
+}

diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c b/tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c
new file mode 100644 (file)
index 0000000..8bc8f7c
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c
@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Facebook */
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+
+extern const struct rq runqueues __ksym; /* struct type global var. */
+extern const int bpf_prog_active __ksym; /* int type global var. */
+
+SEC("raw_tp/sys_enter")
+int handler(const void *ctx)
+{
+       struct rq *rq;
+       int *active;
+       __u32 cpu;
+
+       cpu = bpf_get_smp_processor_id();
+       rq = (struct rq *)bpf_per_cpu_ptr(&runqueues, cpu);
+       active = (int *)bpf_per_cpu_ptr(&bpf_prog_active, cpu);
+       if (active) {
+               /* READ_ONCE */
+               *(volatile int *)active;
+               /* !rq has not been tested, so verifier should reject. */
+               *(volatile int *)(&rq->cpu);
+       }
+
+       return 0;
+}
+
+char _license[] SEC("license") = "GPL";