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 2BA94C43334 for ; Wed, 20 Jul 2022 23:05:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231395AbiGTXFY (ORCPT ); Wed, 20 Jul 2022 19:05:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231387AbiGTXFW (ORCPT ); Wed, 20 Jul 2022 19:05:22 -0400 Received: from mail-io1-xd35.google.com (mail-io1-xd35.google.com [IPv6:2607:f8b0:4864:20::d35]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 69D34A187 for ; Wed, 20 Jul 2022 16:05:20 -0700 (PDT) Received: by mail-io1-xd35.google.com with SMTP id n138so99756iod.4 for ; Wed, 20 Jul 2022 16:05:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=m1T4qbDxhSzNmOGzCQwvKdvIhsg9ftO1mwgvo87Nrw8=; b=bhybBTw1im+DhwPHQWv+PzdM9trpgtKREb+kM6QNvHD05jCfagtV+lxooUJ731yakd AtmTTjzC8ckolKZiHiuVoq5DcUcI7f0G3HBUlfBmed4XPivrb/aOGboWYwHTinfh/++2 KRREJxhfTSMu6dTk41fjcd+Bqsc5KPFtBHWAbuwg8IPFwwXIE//5nOy4HCjcrxn47h40 mLXHvQIlkmaXgPe8ZDzmvua0rHVH5BFWYJyCkSblCjWPH1/rObx2gAxsel7HdAEjQ3FR fmrAxAKRzPK/ulKi/nMXeHIsh58mE9P7jvbmC3e7oo0ga1aE+dxNq4jKi8+XsEwstDfN YTIw== 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=m1T4qbDxhSzNmOGzCQwvKdvIhsg9ftO1mwgvo87Nrw8=; b=CBp9R4ED60qgFThFtcjoQhhjrm6dIu5WJaS7uJoVtD6LB7kiCqIu6wrBXqXBCPwhdK WlFRE9Fyl3Aiy8Vi7rnt3sU7a8xBRAIv2M3PmSadu7JRGSqtRg1hHwkSTHJlwXtqbRzc mNOzHgbfCxrF7MgVjSuQBDjOeSVoNkbt587Cvv0Qn6MeEL4lVJTGHRQQxa6piF+2/mDT Z0qNRzyOAxcNaWGNdIhA67J1OJLPIju/o50LWiKdXuLlK95g1kYirEmN3cD4QbPE3Qka suec18sF0tQ8LqWxHA68liGwcZrTUVzgq3Lqd4UHga13zhQSb949tWdmyoXWL7qsAtbd wJlQ== X-Gm-Message-State: AJIora+2nBtyRq56Hx3s0rudYzi8rNDuDhCRFVIVaTPWoqIxLLQzRaDz vGWna3yQp2tKZaQhWPW1p0MwBvDv4u1MTYoAUXLFhw== X-Google-Smtp-Source: AGRyM1vHwHvPWd8988+SD0LKzqKrSlWnqr4l9t8oZmoloK10ndRc8Ai0iTZof6+FZFo8o5tMT3S8rrmuJp1srFev0W4= X-Received: by 2002:a05:6602:2f03:b0:678:9c7c:97a5 with SMTP id q3-20020a0566022f0300b006789c7c97a5mr18761335iow.32.1658358319643; Wed, 20 Jul 2022 16:05:19 -0700 (PDT) MIME-Version: 1.0 References: <20220719195628.3415852-1-axelrasmussen@google.com> In-Reply-To: From: Axel Rasmussen Date: Wed, 20 Jul 2022 16:04:43 -0700 Message-ID: Subject: Re: [PATCH v4 0/5] userfaultfd: add /dev/userfaultfd for fine grained access control To: "Schaufler, Casey" Cc: Alexander Viro , Andrew Morton , Dave Hansen , "Dmitry V . Levin" , Gleb Fotengauer-Malinovskiy , Hugh Dickins , Jan Kara , Jonathan Corbet , Mel Gorman , Mike Kravetz , Mike Rapoport , "Amit, Nadav" , Peter Xu , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , zhangyi , "linux-doc@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kselftest@vger.kernel.org" , Andrea Arcangeli Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Wed, Jul 20, 2022 at 3:16 PM Schaufler, Casey wrote: > > > -----Original Message----- > > From: Axel Rasmussen > > Sent: Tuesday, July 19, 2022 12:56 PM > > To: Alexander Viro ; Andrew Morton > > ; Dave Hansen > > ; Dmitry V . Levin ; Gleb > > Fotengauer-Malinovskiy ; Hugh Dickins > > ; Jan Kara ; Jonathan Corbet > > ; Mel Gorman ; Mike > > Kravetz ; Mike Rapoport ; > > Amit, Nadav ; Peter Xu ; > > Shuah Khan ; Suren Baghdasaryan > > ; Vlastimil Babka ; zhangyi > > > > Cc: Axel Rasmussen ; linux- > > doc@vger.kernel.org; linux-fsdevel@vger.kernel.org; linux- > > kernel@vger.kernel.org; linux-mm@kvack.org; linux- > > kselftest@vger.kernel.org > > Subject: [PATCH v4 0/5] userfaultfd: add /dev/userfaultfd for fine grained > > access control > > I assume that leaving the LSM mailing list off of the CC is purely > accidental. Please, please include us in the next round. Honestly it just hadn't occurred to me, but I'm more than happy to CC it on future revisions. > > > > > This series is based on torvalds/master. > > > > The series is split up like so: > > - Patch 1 is a simple fixup which we should take in any case (even by itself). > > - Patches 2-6 add the feature, configurable selftest support, and docs. > > > > Why not ...? > > ============ > > > > - Why not /proc/[pid]/userfaultfd? The proposed use case for this is for one > > process to open a userfaultfd which can intercept another process' page > > faults. This seems to me like exactly what CAP_SYS_PTRACE is for, though, > > so I > > think this use case can simply use a syscall without the powers > > CAP_SYS_PTRACE > > grants being "too much". > > > > - Why not use a syscall? Access to syscalls is generally controlled by > > capabilities. We don't have a capability which is used for userfaultfd access > > without also granting more / other permissions as well, and adding a new > > capability was rejected [1]. > > > > - It's possible a LSM could be used to control access instead. I suspect > > adding a brand new one just for this would be rejected, > > You won't know if you don't ask. Fair enough - I wonder if MM folks (Andrew, Peter, Nadav especially) would find that approach more palatable than /proc/[pid]/userfaultfd? Would it make sense from our perspective to propose a userfaultfd- or MM-specific LSM for controlling access to certain features? I remember +Andrea saying Red Hat was also interested in some kind of access control mechanism like this. Would one or the other approach be more convenient for you? > > > but I think some > > existing ones like SELinux can be used to filter syscall access. Enabling > > SELinux for large production deployments which don't already use it is > > likely to be a huge undertaking though, and I don't think this use case by > > itself is enough to motivate that kind of architectural change. > > > > Changelog > > ========= > > > > v3->v4: > > - Picked up an Acked-by on 5/5. > > - Updated cover letter to cover "why not ...". > > - Refactored userfaultfd_allowed() into userfaultfd_syscall_allowed(). > > [Peter] > > - Removed obsolete comment from a previous version. [Peter] > > - Refactored userfaultfd_open() in selftest. [Peter] > > - Reworded admin-guide documentation. [Mike, Peter] > > - Squashed 2 commits adding /dev/userfaultfd to selftest and making > > selftest > > configurable. [Peter] > > - Added "syscall" test modifier (the default behavior) to selftest. [Peter] > > > > v2->v3: > > - Rebased onto linux-next/akpm-base, in order to be based on top of the > > run_vmtests.sh refactor which was merged previously. > > - Picked up some Reviewed-by's. > > - Fixed ioctl definition (_IO instead of _IOWR), and stopped using > > compat_ptr_ioctl since it is unneeded for ioctls which don't take a pointer. > > - Removed the "handle_kernel_faults" bool, simplifying the code. The result > > is > > logically equivalent, but simpler. > > - Fixed userfaultfd selftest so it returns KSFT_SKIP appropriately. > > - Reworded documentation per Shuah's feedback on v2. > > - Improved example usage for userfaultfd selftest. > > > > v1->v2: > > - Add documentation update. > > - Test *both* userfaultfd(2) and /dev/userfaultfd via the selftest. > > > > [1]: https://lore.kernel.org/lkml/686276b9-4530-2045-6bd8- > > 170e5943abe4@schaufler-ca.com/T/ > > > > Axel Rasmussen (5): > > selftests: vm: add hugetlb_shared userfaultfd test to run_vmtests.sh > > userfaultfd: add /dev/userfaultfd for fine grained access control > > userfaultfd: selftests: modify selftest to use /dev/userfaultfd > > userfaultfd: update documentation to describe /dev/userfaultfd > > selftests: vm: add /dev/userfaultfd test cases to run_vmtests.sh > > > > Documentation/admin-guide/mm/userfaultfd.rst | 41 +++++++++++- > > Documentation/admin-guide/sysctl/vm.rst | 3 + > > fs/userfaultfd.c | 69 ++++++++++++++++---- > > include/uapi/linux/userfaultfd.h | 4 ++ > > tools/testing/selftests/vm/run_vmtests.sh | 11 +++- > > tools/testing/selftests/vm/userfaultfd.c | 69 +++++++++++++++++--- > > 6 files changed, 169 insertions(+), 28 deletions(-) > > > > -- > > 2.37.0.170.g444d1eabd0-goog >