Thanks Martin for catching and fixing this!
On Mon, Oct 19, 2020 at 12:43 PM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> 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@xxxxxx>
> ---
> .../selftests/bpf/prog_tests/ksyms_btf.c | 57 +++++++++++++------
> .../bpf/progs/test_ksyms_btf_null_check.c | 31 ++++++++++
> 2 files changed, 70 insertions(+), 18 deletions(-)
> create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms_btf_null_check.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c b/tools/testing/selftests/bpf/prog_tests/ksyms_btf.c
> index 28e26bd3e0ca..b58b775d19f3 100644
> --- 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
> index 000000000000..8bc8f7c637bc
> --- /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";
> --
> 2.24.1
>
