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

[Marcus Wichelmann <marcus.wichelmann@hetzner-cloud.de>]

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?

# 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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