From patchwork Wed Aug 18 23:41:41 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Xu X-Patchwork-Id: 12445545 X-Patchwork-Delegate: bpf@iogearbox.net Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-23.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C25B4C432BE for ; Wed, 18 Aug 2021 23:41:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95A6B60FC4 for ; Wed, 18 Aug 2021 23:41:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234942AbhHRXmd (ORCPT ); Wed, 18 Aug 2021 19:42:33 -0400 Received: from new4-smtp.messagingengine.com ([66.111.4.230]:52991 "EHLO new4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234860AbhHRXma (ORCPT ); Wed, 18 Aug 2021 19:42:30 -0400 Received: from compute5.internal (compute5.nyi.internal [10.202.2.45]) by mailnew.nyi.internal (Postfix) with ESMTP id 64F3D580E0B; Wed, 18 Aug 2021 19:41:55 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute5.internal (MEProxy); Wed, 18 Aug 2021 19:41:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dxuuu.xyz; h= from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; s=fm1; bh=Yk3euvXXlMCwY vGhvhfMir2QOXlVuyuGj4zvye1lxR8=; b=CJkcBFuIyHHZndihoY2jocWg5WF/9 g07b8+jeGMwgwtmO2H/K3sqX0X427JFal0Chw8HhAXKeMaFqrI21Q5zhimCp5xqN c23GHoLCYsNO+eyD81Zn2cS2CmeDwfmDFLyv5jPEHSHUijQGiSyAaV72Q9kuEqUB bXP4OCizYzSA+0bAhdCDWkXVjfcGZo1bHDceL1GGH1zI0AFFdnpf/fJkXX9qEQfW e7LGrOml/Jxgdh75T3BegLTILJJP54sBBxqVZvd9Kg4b2tGAm5prgoWVQXlwJFxS 32B3lAMifXMpoYZuo/1en0aScnMmPpgUSwqO9qxFcfjZCTS4dilNpBLLg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm3; bh=Yk3euvXXlMCwYvGhvhfMir2QOXlVuyuGj4zvye1lxR8=; b=j3K1KuOo 0GEFw0iMAfQlbN+sK5oaDbgGJzipgQ8Cb3U7pj6dnZetDSN82BjOmsq0iEV4w6Xv hbYjswvth7QkXjsy+7lbEH8Y32IycKJD/VJAZyKplfWuGnuivDwQu9sG1FbRjosQ uzSDQcIBwRzk7reI3Qpdj2Zcju2uMwdyLLuFsnofVeqYdEVfW0bIeJfqvsXxerrb 4SoURgVTk7xxzy02X8KSTq0di7IQqr8xnNgq4HUMzUCk8luPDLUOv4fY2piEetRb TKUSOZ70lwRrIbXK79odCq38PjepXmYOkhA3rYOfKEoawKbZRYzOmoO7iCZgTho7 SmqSDjkBOJwtxA== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvtddrleeigddvgecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecufghrlhcuvffnffculddvfedmnegovehorghsthgrlh dqhfeguddvqddtvdculdduhedtmdenucfjughrpefhvffufffkofgjfhgggfestdekredt redttdenucfhrhhomhepffgrnhhivghlucgiuhcuoegugihusegugihuuhhurdighiiiqe enucggtffrrghtthgvrhhnpeeugfffffduffekueetieefgeeltdevfeekhffggeeikeej vdduteevkeeugedvtdenucffohhmrghinheplhhkmhhlrdhorhhgpdhgihhthhhusgdrtg homhenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhgrihhlfhhrohhmpegu gihusegugihuuhhurdighiii X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Wed, 18 Aug 2021 19:41:54 -0400 (EDT) From: Daniel Xu To: bpf@vger.kernel.org, yhs@fb.com, andriin@fb.com Cc: Daniel Xu , kernel-team@fb.com, linux-kernel@vger.kernel.org Subject: [PATCH bpf-next 1/2] bpf: Add bpf_task_pt_regs() helper Date: Wed, 18 Aug 2021 16:41:41 -0700 Message-Id: <6d269f13f2ff742e319a8c19112ef40f0b4c2f46.1629329560.git.dxu@dxuuu.xyz> X-Mailer: git-send-email 2.33.0 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net The motivation behind this helper is to access userspace pt_regs in a kprobe handler. uprobe's ctx is the userspace pt_regs. kprobe's ctx is the kernelspace pt_regs. bpf_task_pt_regs() allows accessing userspace pt_regs in a kprobe handler. The final case (kernelspace pt_regs in uprobe) is pretty rare (usermode helper) so I think that can be solved later if necessary. More concretely, this helper is useful in doing BPF-based DWARF stack unwinding. Currently the kernel can only do framepointer based stack unwinds for userspace code. This is because the DWARF state machines are too fragile to be computed in kernelspace [0]. The idea behind DWARF-based stack unwinds w/ BPF is to copy a chunk of the userspace stack (while in prog context) and send it up to userspace for unwinding (probably with libunwind) [1]. This would effectively enable profiling applications with -fomit-frame-pointer using kprobes and uprobes. [0]: https://lkml.org/lkml/2012/2/10/356 [1]: https://github.com/danobi/bpf-dwarf-walk Signed-off-by: Daniel Xu --- include/uapi/linux/bpf.h | 7 +++++++ kernel/trace/bpf_trace.c | 20 ++++++++++++++++++++ tools/include/uapi/linux/bpf.h | 7 +++++++ 3 files changed, 34 insertions(+) diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index c4f7892edb2b..47427493206a 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -4871,6 +4871,12 @@ union bpf_attr { * Return * Value specified by user at BPF link creation/attachment time * or 0, if it was not specified. + * + * long bpf_task_pt_regs(struct task_struct *task) + * Description + * Get the struct pt_regs associated with **task**. + * Return + * A pointer to struct pt_regs. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -5048,6 +5054,7 @@ union bpf_attr { FN(timer_cancel), \ FN(get_func_ip), \ FN(get_attach_cookie), \ + FN(task_pt_regs), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index cbc73c08c4a4..5924bb5a1462 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -723,6 +723,24 @@ static const struct bpf_func_proto bpf_get_current_task_btf_proto = { .ret_btf_id = &bpf_get_current_btf_ids[0], }; +BPF_CALL_1(bpf_task_pt_regs, struct task_struct *, task) +{ + return (unsigned long) task_pt_regs(task); +} + +BTF_ID_LIST(bpf_task_pt_regs_ids) +BTF_ID(struct, task_struct) +BTF_ID(struct, pt_regs) + +static const struct bpf_func_proto bpf_task_pt_regs_proto = { + .func = bpf_task_pt_regs, + .gpl_only = true, + .arg1_type = ARG_PTR_TO_BTF_ID, + .arg1_btf_id = &bpf_task_pt_regs_ids[0], + .ret_type = RET_PTR_TO_BTF_ID, + .ret_btf_id = &bpf_task_pt_regs_ids[1], +}; + BPF_CALL_2(bpf_current_task_under_cgroup, struct bpf_map *, map, u32, idx) { struct bpf_array *array = container_of(map, struct bpf_array, map); @@ -1032,6 +1050,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_get_current_task_proto; case BPF_FUNC_get_current_task_btf: return &bpf_get_current_task_btf_proto; + case BPF_FUNC_task_pt_regs: + return &bpf_task_pt_regs_proto; case BPF_FUNC_get_current_uid_gid: return &bpf_get_current_uid_gid_proto; case BPF_FUNC_get_current_comm: diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h index c4f7892edb2b..47427493206a 100644 --- a/tools/include/uapi/linux/bpf.h +++ b/tools/include/uapi/linux/bpf.h @@ -4871,6 +4871,12 @@ union bpf_attr { * Return * Value specified by user at BPF link creation/attachment time * or 0, if it was not specified. + * + * long bpf_task_pt_regs(struct task_struct *task) + * Description + * Get the struct pt_regs associated with **task**. + * Return + * A pointer to struct pt_regs. */ #define __BPF_FUNC_MAPPER(FN) \ FN(unspec), \ @@ -5048,6 +5054,7 @@ union bpf_attr { FN(timer_cancel), \ FN(get_func_ip), \ FN(get_attach_cookie), \ + FN(task_pt_regs), \ /* */ /* integer value in 'imm' field of BPF_CALL instruction selects which helper