Re: [PATCHv2 bpf-next 6/6] selftests/bpf: Fix get_func_ip offset test for CONFIG_X86_KERNEL_IBT

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Thu, Aug 11, 2022 at 2:16 AM Jiri Olsa <jolsa@kernel.org> wrote:
>
> With CONFIG_X86_KERNEL_IBT enabled the test for kprobe with offset
> won't work because of the extra endbr instruction.
>
> As suggested by Andrii adding CONFIG_X86_KERNEL_IBT detection
> and using appropriate offset value based on that.
>
> Also removing test7 program, because it does the same as test6.
>
> Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
>  .../bpf/prog_tests/get_func_ip_test.c         | 62 +++++++++++++++----
>  .../selftests/bpf/progs/get_func_ip_test.c    | 20 +++---
>  2 files changed, 60 insertions(+), 22 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c b/tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c
> index 938dbd4d7c2f..a4dab2fa2258 100644
> --- a/tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c
> +++ b/tools/testing/selftests/bpf/prog_tests/get_func_ip_test.c
> @@ -2,7 +2,9 @@
>  #include <test_progs.h>
>  #include "get_func_ip_test.skel.h"
>
> -void test_get_func_ip_test(void)
> +static int config_ibt;
> +
> +static void test_function_entry(void)
>  {
>         struct get_func_ip_test *skel = NULL;
>         int err, prog_fd;
> @@ -12,14 +14,6 @@ void test_get_func_ip_test(void)
>         if (!ASSERT_OK_PTR(skel, "get_func_ip_test__open"))
>                 return;
>
> -       /* test6 is x86_64 specifc because of the instruction
> -        * offset, disabling it for all other archs
> -        */
> -#ifndef __x86_64__
> -       bpf_program__set_autoload(skel->progs.test6, false);
> -       bpf_program__set_autoload(skel->progs.test7, false);
> -#endif
> -
>         err = get_func_ip_test__load(skel);
>         if (!ASSERT_OK(err, "get_func_ip_test__load"))
>                 goto cleanup;
> @@ -38,16 +32,62 @@ void test_get_func_ip_test(void)
>
>         ASSERT_OK(err, "test_run");
>
> +       config_ibt = skel->bss->config_ibt;

skel->bss->config_ibt isn't actually necessary, you can just check
skel->kconfig->CONFIG_X86_KERNEL_IBT directly. And you won't need to
trigger BPF program unnecessary, libbpf will fill out kconfig section
during object/skeleton load phase.

> +       ASSERT_TRUE(config_ibt == 0 || config_ibt == 1, "config_ibt");

you won't need this anymore

> +       printf("%s:config_ibt %d\n", __func__, config_ibt);

and this is just debug leftover

> +
>         ASSERT_EQ(skel->bss->test1_result, 1, "test1_result");
>         ASSERT_EQ(skel->bss->test2_result, 1, "test2_result");
>         ASSERT_EQ(skel->bss->test3_result, 1, "test3_result");
>         ASSERT_EQ(skel->bss->test4_result, 1, "test4_result");
>         ASSERT_EQ(skel->bss->test5_result, 1, "test5_result");
> +

[...]

> diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> index 6db70757bc8b..cb8e58183d46 100644
> --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> @@ -2,6 +2,7 @@
>  #include <linux/bpf.h>
>  #include <bpf/bpf_helpers.h>
>  #include <bpf/bpf_tracing.h>
> +#include <stdbool.h>
>
>  char _license[] SEC("license") = "GPL";
>
> @@ -13,12 +14,19 @@ extern const void bpf_modify_return_test __ksym;
>  extern const void bpf_fentry_test6 __ksym;
>  extern const void bpf_fentry_test7 __ksym;
>
> +extern bool CONFIG_X86_KERNEL_IBT __kconfig __weak;
> +
> +bool config_ibt;
> +
>  __u64 test1_result = 0;
>  SEC("fentry/bpf_fentry_test1")
>  int BPF_PROG(test1, int a)
>  {
>         __u64 addr = bpf_get_func_ip(ctx);
>
> +       /* just to propagate config option value to user space */
> +       config_ibt = CONFIG_X86_KERNEL_IBT;
> +

as mentioned above, you shouldn't need it, just read
CONFIG_X86_KERNEL_IBT directly through skeleton

>         test1_result = (const void *) addr == &bpf_fentry_test1;
>         return 0;
>  }
> @@ -64,7 +72,7 @@ int BPF_PROG(test5, int a, int *b, int ret)
>  }
>
>  __u64 test6_result = 0;
> -SEC("kprobe/bpf_fentry_test6+0x5")
> +SEC("?kprobe/")

don't leave / at the end (and I thought that libbpf rejects this,
isn't that a case?...), just SEC("?kprobe")


>  int test6(struct pt_regs *ctx)
>  {
>         __u64 addr = bpf_get_func_ip(ctx);
> @@ -72,13 +80,3 @@ int test6(struct pt_regs *ctx)
>         test6_result = (const void *) addr == 0;
>         return 0;
>  }
> -
> -__u64 test7_result = 0;
> -SEC("kprobe/bpf_fentry_test7+5")
> -int test7(struct pt_regs *ctx)
> -{
> -       __u64 addr = bpf_get_func_ip(ctx);
> -
> -       test7_result = (const void *) addr == 0;
> -       return 0;
> -}
> --
> 2.37.1
>