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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.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 12:07:12 -0800	[thread overview]
Message-ID: <CAEf4BzbqP1os=mB-WjQNareKumQrGUeqVEw8f+WZwKxN3Kq77A@mail.gmail.com> (raw)
In-Reply-To: <c8c18806-69ce-02f7-bb60-e2b2be30a809@fb.com>

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.

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

  reply	other threads:[~2022-01-21 20:07 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 [this message]
2022-01-21 21:15           ` Yonghong Song
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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