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Date:   Mon, 19 Oct 2020 17:33:22 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf 3/3] bpf: selftest: Ensure the return value of the
 bpf_per_cpu_ptr() must be checked

Thanks Martin for catching and fixing this!


On Mon, Oct 19, 2020 at 12:43 PM Martin KaFai Lau <kafai@...com> 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@...com>
> ---
>  .../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
>

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