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 X-Spam-Level: X-Spam-Status: No, score=-2.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT autolearn=unavailable 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 42875C10F00 for ; Fri, 22 Feb 2019 19:35:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CECA2070B for ; Fri, 22 Feb 2019 19:35:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="LcyuQXbr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726477AbfBVTfD (ORCPT ); Fri, 22 Feb 2019 14:35:03 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:43389 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725900AbfBVTfC (ORCPT ); Fri, 22 Feb 2019 14:35:02 -0500 Received: by mail-pl1-f194.google.com with SMTP id m10so1514093plt.10; Fri, 22 Feb 2019 11:35:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=gH7xotXdQAwAgaSglUrReQ/sVHSX+EVbzBTwLX0BHOA=; b=LcyuQXbrtLQQ7icLYjdeo/eNu8cn3IPr9IMu9O8ly4Ulg13HueqXzrH/jABYt3N2/t 7lPUVzmBON768/FQWvf2CGNQzkM46XmnnBsI5NmMW3YZNSK4v6dbdIzHJ86RS+F4LVzs F2gqbR4GlmEsU7MndBYojmd1Ew0L8e+PjYcN2gdOyvr2FgCcR/BRuyaKz+VqiZFJa2jU +z8wS3ZDlU3kLO6lQuVowtriUvvZqqbYilCoqZ0B14QxduFwKC0zZt31HUjKnDjvLByz NlHkxrW5y7UnaaUG2XagxJy7xu0fK69uJKYrwm9Ez2Xe1vlYQOC0FqgIXFqo70LVvuzq krLw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=gH7xotXdQAwAgaSglUrReQ/sVHSX+EVbzBTwLX0BHOA=; b=nw9+DtZLkT2ttJ+oveZADAXDu9Ap28YpaEXXZhulzRPyCnfF1jOJ5eU+f4ym0fg/wM 8tJ4KOtlcgR2pmIto2JRMXKVl9t5HTVsCLmcAhelzcoDROEUC0hBZ0a2Wl1RoY+bJFGj 9Tza4pZOI+1I48Feew7AMmfaqbcqqKBuceW0MLrzyhK1jO9p1DM3vHIrwXhi15m79FoL FyonDwQ7AsWCZVD87nz23UwF6AlYQa1lDIpHbS/qrTAfGW0S3NrQCGAInf5F2vEoW4Fq 92Ei5IEAnSQrwjAaGnngh49bGt4jgvxszuzaeVLWR1Gq3FS54Q9hW/qdBJeQHCzviKJU Fylg== X-Gm-Message-State: AHQUAuYMdkvNEsdmIH7oDJaT8MeJnAd6wd0HJ/rDaDSy9CIAJKo2ZLNP ysljkx2EKRbQ/st/KIhWOu/84eIg X-Google-Smtp-Source: AHgI3IaQpW+QYkdUJ84Y4HD5WqnJuC9KdpufcZAENqwZH7X8MK8eESUgpXzc86Q9+6Qx6wyhS8ARWQ== X-Received: by 2002:a17:902:1:: with SMTP id 1mr5492441pla.276.1550864101584; Fri, 22 Feb 2019 11:35:01 -0800 (PST) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:200::4:1d52]) by smtp.gmail.com with ESMTPSA id u24sm3114817pfm.140.2019.02.22.11.34.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Feb 2019 11:35:00 -0800 (PST) Date: Fri, 22 Feb 2019 11:34:58 -0800 From: Alexei Starovoitov To: Steven Rostedt Cc: Linus Torvalds , Masami Hiramatsu , Andy Lutomirski , Linux List Kernel Mailing , Ingo Molnar , Andrew Morton , stable , Changbin Du , Jann Horn , Kees Cook , Andy Lutomirski , daniel@iogearbox.net, netdev@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault Message-ID: <20190222193456.5vqppubzrcx5wsul@ast-mbp.dhcp.thefacebook.com> References: <20190219111802.1d6dbaa3@gandalf.local.home> <20190219140330.5dd9e876@gandalf.local.home> <20190220171019.5e81a4946b56982f324f7c45@kernel.org> <20190220094926.0ab575b3@gandalf.local.home> <20190222172745.2c7205d62003c0a858e33278@kernel.org> <20190222173509.88489b7c5d1bf0e2ec2382ee@kernel.org> <20190222192703.epvgxghwybte7gxs@ast-mbp.dhcp.thefacebook.com> <20190222143026.17d6f0f6@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190222143026.17d6f0f6@gandalf.local.home> User-Agent: NeoMutt/20180223 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 22, 2019 at 02:30:26PM -0500, Steven Rostedt wrote: > On Fri, 22 Feb 2019 11:27:05 -0800 > Alexei Starovoitov wrote: > > > On Fri, Feb 22, 2019 at 09:43:14AM -0800, Linus Torvalds wrote: > > > > > > Then we should still probably fix up "__probe_kernel_read()" to not > > > allow user accesses. The easiest way to do that is actually likely to > > > use the "unsafe_get_user()" functions *without* doing a > > > uaccess_begin(), which will mean that modern CPU's will simply fault > > > on a kernel access to user space. > > > > On bpf side the bpf_probe_read() helper just calls probe_kernel_read() > > and users pass both user and kernel addresses into it and expect > > that the helper will actually try to read from that address. > > > > If __probe_kernel_read will suddenly start failing on all user addresses > > it will break the expectations. > > How do we solve it in bpf_probe_read? > > Call probe_kernel_read and if that fails call unsafe_get_user byte-by-byte > > in the loop? > > That's doable, but people already complain that bpf_probe_read() is slow > > and shows up in their perf report. > > We're changing kprobes to add a specific flag to say that we want to > differentiate between kernel or user reads. Can this be done with > bpf_probe_read()? If it's showing up in perf report, I doubt a single so you're saying you will break existing kprobe scripts? I don't think it's a good idea. It's not acceptable to break bpf_probe_read uapi.