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From: Yonghong Song <yhs@fb.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: Kenny Yu <kennyyu@fb.com>, Andrii Nakryiko <andrii@kernel.org>,
	Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Gabriele <phoenix1987@gmail.com>
Subject: Re: [PATCH v6 bpf-next 1/3] bpf: Add bpf_copy_from_user_task() helper
Date: Fri, 21 Jan 2022 13:15:34 -0800	[thread overview]
Message-ID: <170be4e4-6709-cfae-f728-81fc4452f111@fb.com> (raw)
In-Reply-To: <CAEf4BzbqP1os=mB-WjQNareKumQrGUeqVEw8f+WZwKxN3Kq77A@mail.gmail.com>



On 1/21/22 12:07 PM, Andrii Nakryiko wrote:
> On Fri, Jan 21, 2022 at 12:04 PM Yonghong Song <yhs@fb.com> wrote:
>>
>>
>>
>> On 1/21/22 11:53 AM, Andrii Nakryiko wrote:
>>> On Fri, Jan 21, 2022 at 11:31 AM Kenny Yu <kennyyu@fb.com> wrote:
>>>>
>>>> This adds a helper for bpf programs to read the memory of other
>>>> tasks. This also adds the ability for bpf iterator programs to
>>>> be sleepable.
>>>>
>>>> This changes `bpf_iter_run_prog` to use the appropriate synchronization for
>>>> sleepable bpf programs. With sleepable bpf iterator programs, we can no
>>>> longer use `rcu_read_lock()` and must use `rcu_read_lock_trace()` instead
>>>> to protect the bpf program.
>>>>
>>>> As an example use case at Meta, we are using a bpf task iterator program
>>>> and this new helper to print C++ async stack traces for all threads of
>>>> a given process.
>>>>
>>>> Signed-off-by: Kenny Yu <kennyyu@fb.com>
>>>> ---
>>>>    include/linux/bpf.h            |  1 +
>>>>    include/uapi/linux/bpf.h       | 10 ++++++++++
>>>>    kernel/bpf/bpf_iter.c          | 20 ++++++++++++++-----
>>>>    kernel/bpf/helpers.c           | 35 ++++++++++++++++++++++++++++++++++
>>>>    kernel/trace/bpf_trace.c       |  2 ++
>>>>    tools/include/uapi/linux/bpf.h | 10 ++++++++++
>>>>    6 files changed, 73 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>>> index 80e3387ea3af..5917883e528b 100644
>>>> --- a/include/linux/bpf.h
>>>> +++ b/include/linux/bpf.h
>>>> @@ -2229,6 +2229,7 @@ extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
>>>>    extern const struct bpf_func_proto bpf_find_vma_proto;
>>>>    extern const struct bpf_func_proto bpf_loop_proto;
>>>>    extern const struct bpf_func_proto bpf_strncmp_proto;
>>>> +extern const struct bpf_func_proto bpf_copy_from_user_task_proto;
>>>>
>>>>    const struct bpf_func_proto *tracing_prog_func_proto(
>>>>      enum bpf_func_id func_id, const struct bpf_prog *prog);
>>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>>>> index fe2272defcd9..d82d9423874d 100644
>>>> --- a/include/uapi/linux/bpf.h
>>>> +++ b/include/uapi/linux/bpf.h
>>>> @@ -5049,6 +5049,15 @@ union bpf_attr {
>>>>     *             This helper is currently supported by cgroup programs only.
>>>>     *     Return
>>>>     *             0 on success, or a negative error in case of failure.
>>>> + *
>>>> + * long bpf_copy_from_user_task(void *dst, u32 size, const void *user_ptr, struct task_struct *tsk, u64 flags)
>>>> + *     Description
>>>> + *             Read *size* bytes from user space address *user_ptr* in *tsk*'s
>>>> + *             address space, and stores the data in *dst*. *flags* is not
>>>> + *             used yet and is provided for future extensibility. This helper
>>>> + *             can only be used by sleepable programs.
>>>
>>> "On error dst buffer is zeroed out."? This is an explicit guarantee.
>>>
>>>> + *     Return
>>>> + *             0 on success, or a negative error in case of failure.
>>>>     */
>>>>    #define __BPF_FUNC_MAPPER(FN)          \
>>>>           FN(unspec),                     \
>>>> @@ -5239,6 +5248,7 @@ union bpf_attr {
>>>>           FN(get_func_arg_cnt),           \
>>>>           FN(get_retval),                 \
>>>>           FN(set_retval),                 \
>>>> +       FN(copy_from_user_task),        \
>>>>           /* */
>>>>
>>>>    /* integer value in 'imm' field of BPF_CALL instruction selects which helper
>>>> diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
>>>> index b7aef5b3416d..110029ede71e 100644
>>>> --- a/kernel/bpf/bpf_iter.c
>>>> +++ b/kernel/bpf/bpf_iter.c
>>>> @@ -5,6 +5,7 @@
>>>>    #include <linux/anon_inodes.h>
>>>>    #include <linux/filter.h>
>>>>    #include <linux/bpf.h>
>>>> +#include <linux/rcupdate_trace.h>
>>>>
>>>>    struct bpf_iter_target_info {
>>>>           struct list_head list;
>>>> @@ -684,11 +685,20 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx)
>>>>    {
>>>>           int ret;
>>>>
>>>> -       rcu_read_lock();
>>>> -       migrate_disable();
>>>> -       ret = bpf_prog_run(prog, ctx);
>>>> -       migrate_enable();
>>>> -       rcu_read_unlock();
>>>> +       if (prog->aux->sleepable) {
>>>> +               rcu_read_lock_trace();
>>>> +               migrate_disable();
>>>> +               might_fault();
>>>> +               ret = bpf_prog_run(prog, ctx);
>>>> +               migrate_enable();
>>>> +               rcu_read_unlock_trace();
>>>> +       } else {
>>>> +               rcu_read_lock();
>>>> +               migrate_disable();
>>>> +               ret = bpf_prog_run(prog, ctx);
>>>> +               migrate_enable();
>>>> +               rcu_read_unlock();
>>>> +       }
>>>>
>>>
>>> I think this sleepable bpf_iter change deserves its own patch. It has
>>> nothing to do with bpf_copy_from_user_task() helper.
>>
>> Without the above change, using bpf_copy_from_user_task() will trigger
>> rcu warning and may produce incorrect result. One option is to put
>> the above in a preparation patch before introducing
>> bpf_copy_from_user_task() so we won't have bisecting issues.
> 
> Sure, patch #1 for sleepable bpf_iter, patch #2 for the helper? I
> mean, it's not a big deal, but both seem to deserve their own focused
> patches.

okay with me.

> 
>>
>>>
>>>>           /* bpf program can only return 0 or 1:
>>>>            *  0 : okay
>> [...]

  reply	other threads:[~2022-01-21 21:15 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-13 23:31 [PATCH bpf-next 0/3] Add bpf_access_process_vm helper and sleepable bpf iterator programs Kenny Yu
2022-01-13 23:31 ` [PATCH bpf-next 1/3] bpf: Add bpf_access_process_vm() helper Kenny Yu
2022-01-13 23:31 ` [PATCH bpf-next 2/3] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-13 23:31 ` [PATCH bpf-next 3/3] selftests/bpf: Add test " Kenny Yu
2022-01-14  0:48 ` [PATCH v2 bpf-next 0/4] Add bpf_access_process_vm helper and " Kenny Yu
2022-01-14  0:48   ` [PATCH v2 bpf-next 1/4] bpf: Add bpf_access_process_vm() helper Kenny Yu
2022-01-14  0:48   ` [PATCH v2 bpf-next 2/4] bpf: Add support for sleepable programs in bpf_iter_run_prog Kenny Yu
2022-01-14  2:50     ` Alexei Starovoitov
2022-01-14 23:15       ` Kenny Yu
2022-01-14  0:48   ` [PATCH v2 bpf-next 3/4] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-14  0:49   ` [PATCH v2 bpf-next 4/4] selftests/bpf: Add test " Kenny Yu
2022-01-14  2:39     ` Alexei Starovoitov
2022-01-14 23:14       ` Kenny Yu
2022-01-15  1:38         ` Andrii Nakryiko
2022-01-15  4:30           ` Kenny Yu
2022-01-15 16:27           ` Gabriele
2022-01-19 16:56             ` Kenny Yu
2022-01-19 18:02 ` [PATCH v3 bpf-next 0/3] Add bpf_access_process_vm helper and " Kenny Yu
2022-01-19 18:02   ` [PATCH v3 bpf-next 1/3] bpf: Add bpf_access_process_vm() helper Kenny Yu
2022-01-19 20:16     ` Alexei Starovoitov
2022-01-19 22:51       ` Kenny Yu
2022-01-19 18:02   ` [PATCH v3 bpf-next 2/3] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-19 18:02   ` [PATCH v3 bpf-next 3/3] selftests/bpf: Add test " Kenny Yu
2022-01-19 22:59 ` [PATCH v4 bpf-next 0/3] Add bpf_access_process_vm helper and " Kenny Yu
2022-01-19 22:59   ` [PATCH v4 bpf-next 1/3] bpf: Add bpf_access_process_vm() helper Kenny Yu
2022-01-20  3:45     ` Yonghong Song
2022-01-20 17:11       ` Kenny Yu
2022-01-19 22:59   ` [PATCH v4 bpf-next 2/3] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-19 22:59   ` [PATCH v4 bpf-next 3/3] selftests/bpf: Add test " Kenny Yu
2022-01-20 17:29 ` [PATCH v5 bpf-next 0/3] Add bpf_access_process_vm helper and " Kenny Yu
2022-01-20 17:29   ` [PATCH v5 bpf-next 1/3] bpf: Add bpf_access_process_vm() helper Kenny Yu
2022-01-20 22:45     ` Andrii Nakryiko
2022-01-21  2:27       ` Alexei Starovoitov
2022-01-21 17:20         ` Andrii Nakryiko
2022-01-21 17:41           ` Kenny Yu
2022-01-21 17:47             ` Alexei Starovoitov
2022-01-21 18:30               ` Kenny Yu
2022-01-20 17:29   ` [PATCH v5 bpf-next 2/3] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-20 17:29   ` [PATCH v5 bpf-next 3/3] selftests/bpf: Add test " Kenny Yu
2022-01-20 22:48     ` Andrii Nakryiko
2022-01-21 19:30 ` [PATCH v6 bpf-next 0/3] Add bpf_copy_from_user_task helper and " Kenny Yu
2022-01-21 19:30   ` [PATCH v6 bpf-next 1/3] bpf: Add bpf_copy_from_user_task() helper Kenny Yu
2022-01-21 19:53     ` Andrii Nakryiko
2022-01-21 20:04       ` Yonghong Song
2022-01-21 20:07         ` Andrii Nakryiko
2022-01-21 21:15           ` Yonghong Song [this message]
2022-01-24 17:30             ` Kenny Yu
2022-01-22  9:58       ` Gabriele
2022-01-22 10:08         ` Gabriele
2022-01-21 19:30   ` [PATCH v6 bpf-next 2/3] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-21 19:54     ` Andrii Nakryiko
2022-01-21 19:30   ` [PATCH v6 bpf-next 3/3] selftests/bpf: Add test " Kenny Yu
2022-01-21 19:55     ` Andrii Nakryiko
2022-01-24 18:53 ` [PATCH v7 bpf-next 0/4] Add bpf_copy_from_user_task helper and " Kenny Yu
2022-01-24 18:54   ` [PATCH v7 bpf-next 1/4] bpf: Add support for bpf iterator programs to use sleepable helpers Kenny Yu
2022-01-24 22:19     ` Andrii Nakryiko
2022-01-24 18:54   ` [PATCH v7 bpf-next 2/4] bpf: Add bpf_copy_from_user_task() helper Kenny Yu
2022-01-24 22:18     ` Andrii Nakryiko
2022-01-25  4:06       ` Alexei Starovoitov
2022-01-24 18:54   ` [PATCH v7 bpf-next 3/4] libbpf: Add "iter.s" section for sleepable bpf iterator programs Kenny Yu
2022-01-24 18:54   ` [PATCH v7 bpf-next 4/4] selftests/bpf: Add test " Kenny Yu
2022-01-25  4:10   ` [PATCH v7 bpf-next 0/4] Add bpf_copy_from_user_task helper and " patchwork-bot+netdevbpf

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