Re: [bpf-next v8 3/3] selftests/bpf: Add tests for bpf_copy_from_user_task_str

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

On Fri, Feb 21, 2025 at 7:01 AM Marcus Wichelmann
<marcus.wichelmann@hetzner-cloud.de> wrote:
>
> Hi,
>
> I'm not sure what I'm doing wrong, but after rebasing on latest bpf-next
> which includes this patch, I'm no longer able to build the bpf selftests:
>
> # pushd tools/testing/selftests/bpf/
> # make -j80
> [...]
>    GEN-SKEL [test_progs] bpf_iter_task_vmas.skel.h
>    CLNG-BPF [test_progs] bpf_iter_tasks.bpf.o
> progs/bpf_iter_tasks.c:98:8: error: call to undeclared function 'bpf_copy_from_user_task_str'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>     98 |         ret = bpf_copy_from_user_task_str((char *)task_str1, sizeof(task_str1), ptr, task, 0);
>        |               ^
> 1 error generated.
> make: *** [Makefile:733: /root/linux/tools/testing/selftests/bpf/bpf_iter_tasks.bpf.o] Error 1
>
> I suppose the function definition should be in the vmlinux.h?
>

Yes, it should be in vmlinux.h, and if you don't have it, then you
must have a bit too old pahole.

$ git tag --contains ce4d0bc0200e3
v1.27
v1.28

> # grep bpf_copy tools/include/vmlinux.h
> typedef u64 (*btf_bpf_copy_from_user)(void *, u32, const void *);
> typedef u64 (*btf_bpf_copy_from_user_task)(void *, u32, const void *, struct task_struct *, u64);
>
> The kernel built from this revision is booted while trying to compile
> the selftests. I can also see that the kfunc is there when dumping without "format c":
>
> # bpftool btf dump file /sys/kernel/btf/vmlinux | grep bpf_copy_from_user_task_str
> [116060] FUNC 'bpf_copy_from_user_task_str' type_id=116059 linkage=static
>
> But when dumping the vmlinux headers with "format c", I cannot see the kfunc.
> I'm not sure if this is normal:
>
> # bpftool btf dump file /sys/kernel/btf/vmlinux format c | grep bpf_copy_from_user_task_str
> #
>
> CONFIG_BPF SYSCALL is enabled. Are there other config options that
> have to be enabled that I may be missing?
>
> I'm trying this on a aarch64 system. I also tried to fully clean
> my working tree using `git clean -d -x -f`, which didn't help
> either.
>
> Thanks!
> Marcus
>
>
> Am 13.02.25 um 16:21 schrieb Jordan Rome:
> > This adds tests for both the happy path and the
> > error path (with and without the BPF_F_PAD_ZEROS flag).
> >
> > Signed-off-by: Jordan Rome <linux@jordanrome.com>
> > ---
> >   .../selftests/bpf/prog_tests/bpf_iter.c       |  68 +++++++++++
> >   .../selftests/bpf/prog_tests/read_vsyscall.c  |   1 +
> >   .../selftests/bpf/progs/bpf_iter_tasks.c      | 110 ++++++++++++++++++
> >   .../selftests/bpf/progs/read_vsyscall.c       |  11 +-
> >   4 files changed, 188 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> > index 6f1bfacd7375..add4a18c33bd 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> > @@ -323,19 +323,87 @@ static void test_task_pidfd(void)
> >   static void test_task_sleepable(void)
> >   {
> >       struct bpf_iter_tasks *skel;
> > +     int pid, status, err, data_pipe[2], finish_pipe[2], c;
> > +     char *test_data = NULL;
> > +     char *test_data_long = NULL;
> > +     char *data[2];
> > +
> > +     if (!ASSERT_OK(pipe(data_pipe), "data_pipe") ||
> > +         !ASSERT_OK(pipe(finish_pipe), "finish_pipe"))
> > +             return;
> >
> >       skel = bpf_iter_tasks__open_and_load();
> >       if (!ASSERT_OK_PTR(skel, "bpf_iter_tasks__open_and_load"))
> >               return;
> >
> > +     pid = fork();
> > +     if (!ASSERT_GE(pid, 0, "fork"))
> > +             return;
> > +
> > +     if (pid == 0) {
> > +             /* child */
> > +             close(data_pipe[0]);
> > +             close(finish_pipe[1]);
> > +
> > +             test_data = malloc(sizeof(char) * 10);
> > +             strncpy(test_data, "test_data", 10);
> > +             test_data[9] = '\0';
> > +
> > +             test_data_long = malloc(sizeof(char) * 5000);
> > +             for (int i = 0; i < 5000; ++i) {
> > +                     if (i % 2 == 0)
> > +                             test_data_long[i] = 'b';
> > +                     else
> > +                             test_data_long[i] = 'a';
> > +             }
> > +             test_data_long[4999] = '\0';
> > +
> > +             data[0] = test_data;
> > +             data[1] = test_data_long;
> > +
> > +             write(data_pipe[1], &data, sizeof(data));
> > +
> > +             /* keep child alive until after the test */
> > +             err = read(finish_pipe[0], &c, 1);
> > +             if (err != 1)
> > +                     exit(-1);
> > +
> > +             close(data_pipe[1]);
> > +             close(finish_pipe[0]);
> > +             _exit(0);
> > +     }
> > +
> > +     /* parent */
> > +     close(data_pipe[1]);
> > +     close(finish_pipe[0]);
> > +
> > +     err = read(data_pipe[0], &data, sizeof(data));
> > +     ASSERT_EQ(err, sizeof(data), "read_check");
> > +
> > +     skel->bss->user_ptr = data[0];
> > +     skel->bss->user_ptr_long = data[1];
> > +     skel->bss->pid = pid;
> > +
> >       do_dummy_read(skel->progs.dump_task_sleepable);
> >
> >       ASSERT_GT(skel->bss->num_expected_failure_copy_from_user_task, 0,
> >                 "num_expected_failure_copy_from_user_task");
> >       ASSERT_GT(skel->bss->num_success_copy_from_user_task, 0,
> >                 "num_success_copy_from_user_task");
> > +     ASSERT_GT(skel->bss->num_expected_failure_copy_from_user_task_str, 0,
> > +               "num_expected_failure_copy_from_user_task_str");
> > +     ASSERT_GT(skel->bss->num_success_copy_from_user_task_str, 0,
> > +               "num_success_copy_from_user_task_str");
> >
> >       bpf_iter_tasks__destroy(skel);
> > +
> > +     write(finish_pipe[1], &c, 1);
> > +     err = waitpid(pid, &status, 0);
> > +     ASSERT_EQ(err, pid, "waitpid");
> > +     ASSERT_EQ(status, 0, "zero_child_exit");
> > +
> > +     close(data_pipe[0]);
> > +     close(finish_pipe[1]);
> >   }
> >
> >   static void test_task_stack(void)
> > diff --git a/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c b/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
> > index c7b9ba8b1d06..a8d1eaa67020 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/read_vsyscall.c
> > @@ -24,6 +24,7 @@ struct read_ret_desc {
> >       { .name = "copy_from_user", .ret = -EFAULT },
> >       { .name = "copy_from_user_task", .ret = -EFAULT },
> >       { .name = "copy_from_user_str", .ret = -EFAULT },
> > +     { .name = "copy_from_user_task_str", .ret = -EFAULT },
> >   };
> >
> >   void test_read_vsyscall(void)
> > diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c b/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
> > index bc10c4e4b4fa..966ee5a7b066 100644
> > --- a/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
> > +++ b/tools/testing/selftests/bpf/progs/bpf_iter_tasks.c
> > @@ -9,6 +9,13 @@ char _license[] SEC("license") = "GPL";
> >   uint32_t tid = 0;
> >   int num_unknown_tid = 0;
> >   int num_known_tid = 0;
> > +void *user_ptr = 0;
> > +void *user_ptr_long = 0;
> > +uint32_t pid = 0;
> > +
> > +static char big_str1[5000];
> > +static char big_str2[5005];
> > +static char big_str3[4996];
> >
> >   SEC("iter/task")
> >   int dump_task(struct bpf_iter__task *ctx)
> > @@ -35,7 +42,9 @@ int dump_task(struct bpf_iter__task *ctx)
> >   }
> >
> >   int num_expected_failure_copy_from_user_task = 0;
> > +int num_expected_failure_copy_from_user_task_str = 0;
> >   int num_success_copy_from_user_task = 0;
> > +int num_success_copy_from_user_task_str = 0;
> >
> >   SEC("iter.s/task")
> >   int dump_task_sleepable(struct bpf_iter__task *ctx)
> > @@ -44,6 +53,9 @@ int dump_task_sleepable(struct bpf_iter__task *ctx)
> >       struct task_struct *task = ctx->task;
> >       static const char info[] = "    === END ===";
> >       struct pt_regs *regs;
> > +     char task_str1[10] = "aaaaaaaaaa";
> > +     char task_str2[10], task_str3[10];
> > +     char task_str4[20] = "aaaaaaaaaaaaaaaaaaaa";
> >       void *ptr;
> >       uint32_t user_data = 0;
> >       int ret;
> > @@ -78,8 +90,106 @@ int dump_task_sleepable(struct bpf_iter__task *ctx)
> >               BPF_SEQ_PRINTF(seq, "%s\n", info);
> >               return 0;
> >       }
> > +
> >       ++num_success_copy_from_user_task;
> >
> > +     /* Read an invalid pointer and ensure we get an error */
> > +     ptr = NULL;
> > +     ret = bpf_copy_from_user_task_str((char *)task_str1, sizeof(task_str1), ptr, task, 0);
> > +     if (ret >= 0 || task_str1[9] != 'a' || task_str1[0] != '\0') {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* Read an invalid pointer and ensure we get error with pad zeros flag */
> > +     ptr = NULL;
> > +     ret = bpf_copy_from_user_task_str((char *)task_str1, sizeof(task_str1),
> > +                                       ptr, task, BPF_F_PAD_ZEROS);
> > +     if (ret >= 0 || task_str1[9] != '\0' || task_str1[0] != '\0') {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     ++num_expected_failure_copy_from_user_task_str;
> > +
> > +     /* Same length as the string */
> > +     ret = bpf_copy_from_user_task_str((char *)task_str2, 10, user_ptr, task, 0);
> > +     /* only need to do the task pid check once */
> > +     if (bpf_strncmp(task_str2, 10, "test_data\0") != 0 || ret != 10 || task->tgid != pid) {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* Shorter length than the string */
> > +     ret = bpf_copy_from_user_task_str((char *)task_str3, 2, user_ptr, task, 0);
> > +     if (bpf_strncmp(task_str3, 2, "t\0") != 0 || ret != 2) {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* Longer length than the string */
> > +     ret = bpf_copy_from_user_task_str((char *)task_str4, 20, user_ptr, task, 0);
> > +     if (bpf_strncmp(task_str4, 10, "test_data\0") != 0 || ret != 10
> > +         || task_str4[sizeof(task_str4) - 1] != 'a') {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* Longer length than the string with pad zeros flag */
> > +     ret = bpf_copy_from_user_task_str((char *)task_str4, 20, user_ptr, task, BPF_F_PAD_ZEROS);
> > +     if (bpf_strncmp(task_str4, 10, "test_data\0") != 0 || ret != 10
> > +         || task_str4[sizeof(task_str4) - 1] != '\0') {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* Longer length than the string past a page boundary */
> > +     ret = bpf_copy_from_user_task_str(big_str1, 5000, user_ptr, task, 0);
> > +     if (bpf_strncmp(big_str1, 10, "test_data\0") != 0 || ret != 10) {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* String that crosses a page boundary */
> > +     ret = bpf_copy_from_user_task_str(big_str1, 5000, user_ptr_long, task, BPF_F_PAD_ZEROS);
> > +     if (bpf_strncmp(big_str1, 4, "baba") != 0 || ret != 5000
> > +         || bpf_strncmp(big_str1 + 4996, 4, "bab\0") != 0) {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     for (int i = 0; i < 4999; ++i) {
> > +             if (i % 2 == 0) {
> > +                     if (big_str1[i] != 'b') {
> > +                             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +                             return 0;
> > +                     }
> > +             } else {
> > +                     if (big_str1[i] != 'a') {
> > +                             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +                             return 0;
> > +                     }
> > +             }
> > +     }
> > +
> > +     /* Longer length than the string that crosses a page boundary */
> > +     ret = bpf_copy_from_user_task_str(big_str2, 5005, user_ptr_long, task, BPF_F_PAD_ZEROS);
> > +     if (bpf_strncmp(big_str2, 4, "baba") != 0 || ret != 5000
> > +         || bpf_strncmp(big_str2 + 4996, 5, "bab\0\0") != 0) {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     /* Shorter length than the string that crosses a page boundary */
> > +     ret = bpf_copy_from_user_task_str(big_str3, 4996, user_ptr_long, task, 0);
> > +     if (bpf_strncmp(big_str3, 4, "baba") != 0 || ret != 4996
> > +         || bpf_strncmp(big_str3 + 4992, 4, "bab\0") != 0) {
> > +             BPF_SEQ_PRINTF(seq, "%s\n", info);
> > +             return 0;
> > +     }
> > +
> > +     ++num_success_copy_from_user_task_str;
> > +
> >       if (ctx->meta->seq_num == 0)
> >               BPF_SEQ_PRINTF(seq, "    tgid      gid     data\n");
> >
> > diff --git a/tools/testing/selftests/bpf/progs/read_vsyscall.c b/tools/testing/selftests/bpf/progs/read_vsyscall.c
> > index 39ebef430059..395591374d4f 100644
> > --- a/tools/testing/selftests/bpf/progs/read_vsyscall.c
> > +++ b/tools/testing/selftests/bpf/progs/read_vsyscall.c
> > @@ -8,14 +8,16 @@
> >
> >   int target_pid = 0;
> >   void *user_ptr = 0;
> > -int read_ret[9];
> > +int read_ret[10];
> >
> >   char _license[] SEC("license") = "GPL";
> >
> >   /*
> > - * This is the only kfunc, the others are helpers
> > + * These are the kfuncs, the others are helpers
> >    */
> >   int bpf_copy_from_user_str(void *dst, u32, const void *, u64) __weak __ksym;
> > +int bpf_copy_from_user_task_str(void *dst, u32, const void *,
> > +                             struct task_struct *, u64) __weak __ksym;
> >
> >   SEC("fentry/" SYS_PREFIX "sys_nanosleep")
> >   int do_probe_read(void *ctx)
> > @@ -47,6 +49,11 @@ int do_copy_from_user(void *ctx)
> >       read_ret[7] = bpf_copy_from_user_task(buf, sizeof(buf), user_ptr,
> >                                             bpf_get_current_task_btf(), 0);
> >       read_ret[8] = bpf_copy_from_user_str((char *)buf, sizeof(buf), user_ptr, 0);
> > +     read_ret[9] = bpf_copy_from_user_task_str((char *)buf,
> > +                                               sizeof(buf),
> > +                                               user_ptr,
> > +                                               bpf_get_current_task_btf(),
> > +                                               0);
> >
> >       return 0;
> >   }
> > --
> > 2.43.5
> >
> >
>
> --
> Best regards,
> Marcus Wichelmann
> Linux Networking Specialist
> Team SDN
>
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