From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7DA38C433F5 for ; Fri, 21 Jan 2022 20:07:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231420AbiAUUHZ (ORCPT ); Fri, 21 Jan 2022 15:07:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230509AbiAUUHY (ORCPT ); Fri, 21 Jan 2022 15:07:24 -0500 Received: from mail-il1-x129.google.com (mail-il1-x129.google.com [IPv6:2607:f8b0:4864:20::129]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 65C11C06173D for ; Fri, 21 Jan 2022 12:07:24 -0800 (PST) Received: by mail-il1-x129.google.com with SMTP id i1so2545092ils.5 for ; Fri, 21 Jan 2022 12:07:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=Cn0ivGwNdXd6i0Ws9/SfUIAhEOJW6kf3CMOx7g7/BIs=; b=b3+5gfyZcFKYNeDFnzoQGCCikvQFeRCpSGHD/egBJ0nZ7u6JBl7hvvQXyZvlC9CQLv YAZDkSZDiWuSWME5MnRIhYf+Xp7iHoJ3McgrvPnHSME6z9UFi8goGk2UmAxhkXj7mRtK Xcptd1UtoD7+95Y1SpmVAc7Y+nrB5LwxkcYNEHV+G9isoEIo+XPcq5yE2gtG3oBfl7mX ru9ZMKQas/2Yc2JIwRagt+ZFBLxa+1oZSmwncfCuFh/A5B92zGidKLrtuePArxdKh+Wu gN8bSB1W8l3RpU9xEVULp4eKVK31t6J71Gn7AaeK29zIWI/WfzmCMk3hfD/Z00IowiIh 7JMA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Cn0ivGwNdXd6i0Ws9/SfUIAhEOJW6kf3CMOx7g7/BIs=; b=riI6kgddvp+QbShpv9hZa94g8jdszqd+5VDxLRXnZs/ff9/roAbREp/c3Gb+NTiiSH 4K/x0TSiakHzWmZfDUEB2pvl/OKA9dpehsRwiNZeOKteYbNcJVxx9szXF/zv4FRk9b/c 4YtfwFEDNypbbOvQC3V6I2CH9jSWhpbGvy82+tqI+Sg1voWycnycR84rz9hdFdjGIQKN 6sTTVmsNhrkWQM6SXQ+s2sHXEjFgerOdAFv91vbpvqjrl6hCcLR57N0b/MrEzgo/BcwR EwMpKqzHz3b1cKYkmibuam4/yhky2Lum6fs2nYMCJEIXaWafaGhWCUezR4N9BSJV7/Qc RZwQ== X-Gm-Message-State: AOAM532ZdII8ARZY6uOwSH1Xj/kzH9i/2jBd62HmlD828DmW5SMrUZ/2 XT5cde921g/GAgWuiy38Y+/cUKmzs3P/PfQ/z4M= X-Google-Smtp-Source: ABdhPJzIBdn74Tbtw4ELrU8mTiZBhxAoDPM+sV3apojZF0/yea8zumU/z06knFZBbcnmUfOIcVaKefiR9gwYnQ+GjOU= X-Received: by 2002:a92:db0b:: with SMTP id b11mr3110285iln.98.1642795643753; Fri, 21 Jan 2022 12:07:23 -0800 (PST) MIME-Version: 1.0 References: <20220113233158.1582743-1-kennyyu@fb.com> <20220121193047.3225019-1-kennyyu@fb.com> <20220121193047.3225019-2-kennyyu@fb.com> In-Reply-To: From: Andrii Nakryiko Date: Fri, 21 Jan 2022 12:07:12 -0800 Message-ID: Subject: Re: [PATCH v6 bpf-next 1/3] bpf: Add bpf_copy_from_user_task() helper To: Yonghong Song Cc: Kenny Yu , Andrii Nakryiko , Alexei Starovoitov , bpf , Daniel Borkmann , Alexei Starovoitov , Gabriele Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Jan 21, 2022 at 12:04 PM Yonghong Song wrote: > > > > On 1/21/22 11:53 AM, Andrii Nakryiko wrote: > > On Fri, Jan 21, 2022 at 11:31 AM Kenny Yu 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 > >> --- > >> 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 > >> #include > >> #include > >> +#include > >> > >> 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 > [...]