linux-kernel - Re: [PATCH bpf-next v6 3/3] selftests/bpf: Skip callback tests if jit is disabled in test

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Date: Mon, 22 Jan 2024 17:08:28 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>, 
	John Fastabend <john.fastabend@...il.com>, Jiri Olsa <jolsa@...nel.org>, 
	Hou Tao <houtao@...weicloud.com>, Song Liu <song@...nel.org>, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v6 3/3] selftests/bpf: Skip callback tests if jit
 is disabled in test_verifier

On Sun, Jan 21, 2024 at 11:57 PM Tiezhu Yang <yangtiezhu@...ngson.cn> wrote:
>
> If CONFIG_BPF_JIT_ALWAYS_ON is not set and bpf_jit_enable is 0, there
> exist 6 failed tests.
>
>   [root@...ux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
>   [root@...ux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
>   [root@...ux bpf]# ./test_verifier | grep FAIL
>   #106/p inline simple bpf_loop call FAIL
>   #107/p don't inline bpf_loop call, flags non-zero FAIL
>   #108/p don't inline bpf_loop call, callback non-constant FAIL
>   #109/p bpf_loop_inline and a dead func FAIL
>   #110/p bpf_loop_inline stack locations for loop vars FAIL
>   #111/p inline bpf_loop call in a big program FAIL
>   Summary: 768 PASSED, 15 SKIPPED, 6 FAILED
>
> The test log shows that callbacks are not allowed in non-JITed programs,
> interpreter doesn't support them yet, thus these tests should be skipped
> if jit is disabled, just handle this case in do_test_single().
>
> With this patch:
>
>   [root@...ux bpf]# echo 0 > /proc/sys/net/core/bpf_jit_enable
>   [root@...ux bpf]# echo 0 > /proc/sys/kernel/unprivileged_bpf_disabled
>   [root@...ux bpf]# ./test_verifier | grep FAIL
>   Summary: 768 PASSED, 21 SKIPPED, 0 FAILED
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> Acked-by: Hou Tao <houtao1@...wei.com>
> Acked-by: Song Liu <song@...nel.org>
> ---
>  tools/testing/selftests/bpf/test_verifier.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> index 1a09fc34d093..cf05448cfe13 100644
> --- a/tools/testing/selftests/bpf/test_verifier.c
> +++ b/tools/testing/selftests/bpf/test_verifier.c
> @@ -74,6 +74,7 @@
>                     1ULL << CAP_BPF)
>  #define UNPRIV_SYSCTL "kernel/unprivileged_bpf_disabled"
>  static bool unpriv_disabled = false;
> +static bool jit_disabled;
>  static int skips;
>  static bool verbose = false;
>  static int verif_log_level = 0;
> @@ -1622,6 +1623,16 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
>         alignment_prevented_execution = 0;
>
>         if (expected_ret == ACCEPT || expected_ret == VERBOSE_ACCEPT) {
> +               if (fd_prog < 0 && saved_errno == EINVAL && jit_disabled) {
> +                       for (i = 0; i < prog_len; i++, prog++) {
> +                               if (!insn_is_pseudo_func(prog))
> +                                       continue;
> +                               printf("SKIP (callbacks are not allowed in non-JITed programs)\n");
> +                               skips++;
> +                               goto close_fds;
> +                       }
> +               }

Wouldn't it be better to add an explicit flag to those tests to mark
that they require JIT enabled, instead of trying to derive this from
analysing their BPF instructions?


> +
>                 if (fd_prog < 0) {
>                         printf("FAIL\nFailed to load prog '%s'!\n",
>                                strerror(saved_errno));
> @@ -1844,6 +1855,8 @@ int main(int argc, char **argv)
>                 return EXIT_FAILURE;
>         }
>
> +       jit_disabled = !is_jit_enabled();
> +
>         /* Use libbpf 1.0 API mode */
>         libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
>
> --
> 2.42.0
>