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=-3.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 254E7CA9EBC for ; Fri, 25 Oct 2019 22:43:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EB94021D81 for ; Fri, 25 Oct 2019 22:43:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ow6OD+X+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725963AbfJYWnV (ORCPT ); Fri, 25 Oct 2019 18:43:21 -0400 Received: from mail-qk1-f194.google.com ([209.85.222.194]:34129 "EHLO mail-qk1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725881AbfJYWnV (ORCPT ); Fri, 25 Oct 2019 18:43:21 -0400 Received: by mail-qk1-f194.google.com with SMTP id f18so3263395qkm.1; Fri, 25 Oct 2019 15:43:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=+2E0rH9gnao9G50mrtVlqLqlh+I5+1po+LaLlLD8SKg=; b=ow6OD+X+WKKpGgEPtOwjm2qe2G+iKtXkEaqdglb6vq9KOYlI21/+XhUZkOjswgFUBx oU14TA5Su22Mp/sl1ZutEiIU/0Iq2lBhKq42x5KXIg9L/xfU7jpziTckvX3NPaZBGilu SA472R9szK7nh6vFmfVKdaIZ/WprwD8NwqC4jr166/7yaHoO/rNw6JUFynIchweLR1PA QULbd33+afumdcz4IJ+d8phoY17K/vsSrA2vge1EYcRXa7PDt70lz7eR2UYicQ1o9UbA F4dip0uha/Isy7b4J6WhiJQP2JTaZAJ2KGETgI6/BozJ0EupM3PASsOxqAoIsHy66Nnv Ay3g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=+2E0rH9gnao9G50mrtVlqLqlh+I5+1po+LaLlLD8SKg=; b=K7ehNDjqEzi0157BMze4DNPsZ1TvOaS4jjoYRAJW0x3hc40HNE4p6j4OGP79ik+t8g 7+jl3zSYCZ5z8G7tgUkkNEUksameNdHha4yp2e9BfAsGYg/9gF5pCqmapenZ7dSpQb/8 OPy0DZAKSdm9jwStFLofStZ0c4+rO9sb7QM2KeXagiOD1N7OClajEAy5TqBogqDO3Z2M I+tCzT8LOBJlC1TLgi3qNXCx37KOxq3R6qjmyZX0wdgFzVZNJ2H0Vwhu0Sx1vN9khZO3 ENydRW5TKcu+dUJ36EO55mBquqVANOlJUnBRouVgMioKipuJP/81xl3f/DJPjPh6CueE AR5Q== X-Gm-Message-State: APjAAAUkJwbTlnC6ncMhXoJTgLK+d/oZJlOEErasa5VcuxTs7fNAntgc s55vQuoueWYRWqj05k8AwZBwS2kESS1wKQBCLieeshf/ X-Google-Smtp-Source: APXvYqwHdfbYgejwUsgPAp1c12ilxYS+VZ4XPhy7iuvoBn5eLwPPsPR2UTTSEji/CBRLcC9l3m3wuPqpU2pT+1OTAUE= X-Received: by 2002:a37:4c13:: with SMTP id z19mr5318532qka.449.1572043400366; Fri, 25 Oct 2019 15:43:20 -0700 (PDT) MIME-Version: 1.0 References: <8e63f4005c7139d88c5c78e2a19f539b2a1ff988.1572010897.git.daniel@iogearbox.net> <20191025221530.GD14547@pc-63.home> In-Reply-To: <20191025221530.GD14547@pc-63.home> From: Andrii Nakryiko Date: Fri, 25 Oct 2019 15:43:08 -0700 Message-ID: Subject: Re: [PATCH bpf-next 1/5] uaccess: Add non-pagefault user-space write function To: Daniel Borkmann Cc: Alexei Starovoitov , bpf , Networking Content-Type: text/plain; charset="UTF-8" Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Oct 25, 2019 at 3:15 PM Daniel Borkmann wrote: > > On Fri, Oct 25, 2019 at 02:53:07PM -0700, Andrii Nakryiko wrote: > > On Fri, Oct 25, 2019 at 1:44 PM Daniel Borkmann wrote: > > > > > > Commit 3d7081822f7f ("uaccess: Add non-pagefault user-space read functions") > > > missed to add probe write function, therefore factor out a probe_write_common() > > > helper with most logic of probe_kernel_write() except setting KERNEL_DS, and > > > add a new probe_user_write() helper so it can be used from BPF side. > > > > > > Again, on some archs, the user address space and kernel address space can > > > co-exist and be overlapping, so in such case, setting KERNEL_DS would mean > > > that the given address is treated as being in kernel address space. > > > > > > Signed-off-by: Daniel Borkmann > > > > LGTM. See an EFAULT comment below, though. > > > > Acked-by: Andrii Nakryiko > > > > [...] > > > > > +/** > > > + * probe_user_write(): safely attempt to write to a user-space location > > > + * @dst: address to write to > > > + * @src: pointer to the data that shall be written > > > + * @size: size of the data chunk > > > + * > > > + * Safely write to address @dst from the buffer at @src. If a kernel fault > > > + * happens, handle that and return -EFAULT. > > > + */ > > > + > > > +long __weak probe_user_write(void __user *dst, const void *src, size_t size) > > > + __attribute__((alias("__probe_user_write"))); > > > > curious, why is there this dance of probe_user_write alias to > > __probe_user_write (and for other pairs of functions as well)? > > Seems done by convention to allow archs to override the __weak marked > functions in order to add additional checks and being able to then call > into the __ prefixed variant. > > > > +long __probe_user_write(void __user *dst, const void *src, size_t size) > > > +{ > > > + long ret = -EFAULT; > > > > This initialization is not necessary, is it? Similarly in > > __probe_user_read higher in this file. > > Not entirely sure what you mean. In both there's access_ok() check before > invoking the common helper. ah, right, if, yeah, never mind then. > > > > + mm_segment_t old_fs = get_fs(); > > > + > > > + set_fs(USER_DS); > > > + if (access_ok(dst, size)) > > > + ret = probe_write_common(dst, src, size); > > > + set_fs(old_fs); > > > + > > > + return ret; > > > +} > > > +EXPORT_SYMBOL_GPL(probe_user_write); > > > > > > /** > > > * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. > > > -- > > > 2.21.0 > > >