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 6CCE3C4332F for ; Fri, 18 Nov 2022 07:30:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241122AbiKRHaD (ORCPT ); Fri, 18 Nov 2022 02:30:03 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241046AbiKRHaA (ORCPT ); Fri, 18 Nov 2022 02:30:00 -0500 Received: from mail-ua1-x931.google.com (mail-ua1-x931.google.com [IPv6:2607:f8b0:4864:20::931]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAEA77D525 for ; Thu, 17 Nov 2022 23:29:55 -0800 (PST) Received: by mail-ua1-x931.google.com with SMTP id w17so996051uam.1 for ; Thu, 17 Nov 2022 23:29:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=p54qIR5QLL/GbqEw0yiS4IlYIk9qC5UNyiTDcMkBSn4=; b=Nt5AmFUFLhnfWqydL8qEy+j1PjDIbojFeMUK80/5hEc8Q3Ze78YL7INPuTc4DEnnKM 8Hcirav0fsjw8wXalXH73l69XkcuVfYVzspphiEHYUSsIaWTdwPu1PmJtDZFGKNaqv7j pM6fjB6NifJrf1KWp3fn8WuuqCMRQKXIr4yDmBYfbnQtC91Nqdsnzc50/QQWA+A2jjDc H0YP42LIPvtpZuczeB8vLR+5AQsnxH6wQDEEvaAf3Gv87JAv2T7HHjKd3f3hxBXzctBI 87X8D2tukpcub6cjz/uig81iomFjFSTZt63ci9b++T4y7TjMLygUgzezKSNIWVxpJDjK cMUQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=p54qIR5QLL/GbqEw0yiS4IlYIk9qC5UNyiTDcMkBSn4=; b=I3DH2F5NzcAspGf85yahp+/xbBaR/JS9lNrJJDYXitI3CkWJ23RpIJW9FMwUGzYdOz n9R4e8VjquYmJCcJFpeECJlCu6lzP1NMZU61MXUM82FG8M+MFShCSGGq3TtjT+dGSV7/ tc3tfD/O3EepTh4o/MXv2Jk/h3w1+rT6sfBmwdQ9Zb/Rn2rMg11jT/bvbSmqpzWgkL/8 tjzt6cE1so9PqjdTrYb5DsOriDs374F8Xb8s6IDxudf943F9TLalDS2FVVzzXciFQIM3 gzJJSlUc5KUZWCPFagvSBoYizmwFX2IwOdYO8qcjt+X3qF1mfqNZc5+I9vCSUyQlt0h2 TqdQ== X-Gm-Message-State: ANoB5pkmhs4CAqNnkwTPUQvIm7Xpofiw6U3uTsEYjA9RaZCB0CbWnkrE fc01QCQx4XCP2qCZ8psijdBvX12Daesu8WmQn3oSHg== X-Google-Smtp-Source: AA0mqf4KU6A3b6Li3zUpy2Lk4NYsLCO5Vb2lIVcs9rriQ0Q+7mChaGrUEW7i5q9Wla6p3bnPzAWT9xBCYnFvII50m5Y= X-Received: by 2002:ab0:238f:0:b0:411:968:212 with SMTP id b15-20020ab0238f000000b0041109680212mr3471849uan.107.1668756594737; Thu, 17 Nov 2022 23:29:54 -0800 (PST) MIME-Version: 1.0 References: <20221106021657.1145519-1-pedro.falcato@gmail.com> <202211061948.46D3F78@keescook> <202211171402.95121B3FD4@keescook> In-Reply-To: <202211171402.95121B3FD4@keescook> From: David Gow Date: Fri, 18 Nov 2022 15:29:43 +0800 Message-ID: Subject: Re: Attaching userspace VM to kernel thread (was Re: [PATCH] fs/binfmt_elf: Fix memsz > filesz handling) To: Kees Cook Cc: Matthew Wilcox , linux-mm@kvack.org, Pedro Falcato , linux-kernel@vger.kernel.org, sam@gentoo.org, Alexander Viro , Eric Biederman , linux-fsdevel@vger.kernel.org, Rich Felker , linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="00000000000011363005edb9ac99" Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org --00000000000011363005edb9ac99 Content-Type: text/plain; charset="UTF-8" On Fri, Nov 18, 2022 at 6:06 AM Kees Cook wrote: > > Hi, > > This has diverged from the original topic a bit, so I've changed the > Subject to hopefully gain visibility. :) > > For KUnit, it would be REALLY nice to have a way to attach a userspace > VM to a kernel thread so we can do userspace memory mapping > manipulation, etc. Neither David nor I have been able to figure out the > right set of steps to make this happen. What are we missing? > > Details below... > > On Wed, Nov 16, 2022 at 12:34:40PM +0800, David Gow wrote: > > On Mon, Nov 7, 2022 at 11:59 AM Kees Cook wrote: > > > > > > On Sun, Nov 06, 2022 at 02:16:57AM +0000, Pedro Falcato wrote: > > > David, has there been any work on adding a way to instantiate > > > userspace VMAs in a KUnit test? I tried to write this myself, but I > > > couldn't figure out how to make the userspace memory mappings appear. > > > Here's my fumbling attempt: > > > https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=devel/kunit/usercopy > > > > > > I really wish KUnit had userspace mapping support -- I have a bunch of > > > unit tests that need to get built up around checking for regressions > > > here, etc. > > > > Hi Kees, > > > > Sorry the the delayed response! > > > > Alas, my attempts to get this to work haven't been much more > > successful than yours. It's definitely something we'd like to support, > > but I confess to not knowing enough about the mm code to know exactly > > what would be involved. > > > > The workaround is to load tests as modules, and use something like > > Vitor's original patch here: > > https://lore.kernel.org/all/20200721174036.71072-1-vitor@massaru.org/ > > > > Basically, using the existing mm of the module loader. Adapting those > > changes to your branch (and fixing a couple of back-to-front KUnit > > assertions) does work for me when built as a module, in an x86_64 vm: > > > > root@slicestar:~# modprobe usercopy_kunit > > [ 52.986290] # Subtest: usercopy > > [ 52.986701] 1..1 > > [ 53.246058] ok 1 - usercopy_test > > [ 53.246628] ok 1 - usercopy > > > > But getting it to work with built-in tests hasn't been successful so > > far. I wondered if we could just piggy-back on init_mm or similar, but > > that doesn't seem to work either. > > > > So, in the short-term, this is only possible for modules. If that's > > useful enough, we can get Vitor's support patch (or something similar) > > in, and just mark any tests module-only (or have them skip if there's > > no mm). Because kunit.py only runs built-in tests, though, it's > > definitely less convenient. > > Thanks for any pointers! :) > > -Kees > > -- > Kees Cook FWIW, I had another quick look at this yesterday, and I suspect that (at least one of) the problem(s) is that function pointers like mm->get_unmapped_area are only setup as part of exec(), so a newly-created mm isn't actually useful. Looking at, e.g., arch_pick_mm_layout(), there's a whole bunch of architecture-dependent stuff here to handle, e.g., 32-bit compat. 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