From: Andrea Arcangeli <aarcange@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
linux-kernel@vger.kernel.org, Hugh Dickins <hughd@google.com>,
Luis Chamberlain <mcgrof@kernel.org>,
Maxime Coquelin <maxime.coquelin@redhat.com>,
kvm@vger.kernel.org, Jerome Glisse <jglisse@redhat.com>,
Pavel Emelyanov <xemul@virtuozzo.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Martin Cracauer <cracauer@cons.org>,
Denis Plotnikov <dplotnikov@virtuozzo.com>,
linux-mm@kvack.org, Marty McFadden <mcfadden8@llnl.gov>,
Maya Gokhale <gokhale2@llnl.gov>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Kees Cook <keescook@chromium.org>, Mel Gorman <mgorman@suse.de>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
linux-fsdevel@vger.kernel.org,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users
Date: Wed, 13 Mar 2019 14:52:30 -0400 [thread overview]
Message-ID: <20190313185230.GH25147@redhat.com> (raw)
In-Reply-To: <3714d120-64e3-702e-6eef-4ef253bdb66d@redhat.com>
Hello,
On Wed, Mar 13, 2019 at 09:22:31AM +0100, Paolo Bonzini wrote:
> On 13/03/19 07:00, Peter Xu wrote:
> >> However, I can imagine more special cases being added for other users. And,
> >> once you have more than one special case then you may want to combine them.
> >> For example, kvm and hugetlbfs together.
> > It looks fine to me if we're using MMF_USERFAULTFD_ALLOW flag upon
> > mm_struct, since that seems to be a very general flag that can be used
> > by anything we want to grant privilege for, not only KVM?
>
> Perhaps you can remove the fork() limitation, and add a new suboption to
> prctl(PR_SET_MM) that sets/resets MMF_USERFAULTFD_ALLOW. If somebody
> wants to forbid unprivileged userfaultfd and use KVM, they'll have to
> use libvirt or some other privileged management tool.
>
> We could also add support for this prctl to systemd, and then one could
> do "systemd-run -pAllowUserfaultfd=yes COMMAND".
systemd can already implement -pAllowUserfaultfd=no with seccomp if it
wants. It can also implement -yes if by default turns off userfaultfd
like firejail -seccomp would do.
If the end goal is to implement the filtering with an userland policy
instead of a kernel policy, seccomp enabled for all services sounds
reasonable. It's very unlikely you'll block only userfaultfd, firejail
-seccomp by default blocks dozen of syscalls that are unnecessary
99.9% of the time.
This is not about implementing an userland flexible policy, it's just
a simple kernel policy, to use until userland disables the kernel
policy to takeover with seccomp across the board.
I wouldn't like this too be too complicated because this is already
theoretically overlapping 100% with seccomp.
hugetlbfs is more complicated to detect, because even if you inherit
it from fork(), the services that mounts the fs may be in a different
container than the one that Oracle that uses userfaultfd later on down
the road from a different context. And I don't think it would be ok to
allow running userfaultfd just because you can open a file in an
hugetlbfs file system. With /dev/kvm it's a bit different, that's
chmod o-r by default.. no luser should be able to open it.
Unless somebody suggests a consistent way to make hugetlbfs "just
work" (like we could achieve clean with CRIU and KVM), I think Oracle
will need a one liner change in the Oracle setup to echo into that
file in addition of running the hugetlbfs mount.
Note that DPDK host bridge process will also need a one liner change
to do a dummy open/close of /dev/kvm to unblock the syscall.
Thanks,
Andrea
next prev parent reply other threads:[~2019-03-13 18:52 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-11 9:36 [PATCH 0/3] userfaultfd: allow to forbid unprivileged users Peter Xu
2019-03-11 9:36 ` [PATCH 1/3] userfaultfd/sysctl: introduce unprivileged_userfaultfd Peter Xu
2019-03-12 6:58 ` Mike Rapoport
2019-03-12 12:26 ` Peter Xu
2019-03-12 13:53 ` Mike Rapoport
2019-03-11 9:37 ` [PATCH 2/3] kvm/mm: introduce MMF_USERFAULTFD_ALLOW flag Peter Xu
2019-03-11 9:37 ` [PATCH 3/3] userfaultfd: apply unprivileged_userfaultfd check Peter Xu
2019-03-11 9:58 ` Peter Xu
2019-03-12 7:01 ` [PATCH 0/3] userfaultfd: allow to forbid unprivileged users Mike Rapoport
2019-03-12 12:29 ` Peter Xu
2019-03-12 7:49 ` Kirill A. Shutemov
2019-03-12 12:43 ` Peter Xu
2019-03-12 19:59 ` Mike Kravetz
2019-03-13 6:00 ` Peter Xu
2019-03-13 8:22 ` Paolo Bonzini
2019-03-13 18:52 ` Andrea Arcangeli [this message]
2019-03-13 19:12 ` Paolo Bonzini
2019-03-13 23:44 ` Andrea Arcangeli
2019-03-14 10:58 ` Paolo Bonzini
2019-03-14 15:23 ` Alexei Starovoitov
2019-03-14 16:00 ` Paolo Bonzini
2019-03-14 16:16 ` Andrea Arcangeli
2019-03-15 16:09 ` Kees Cook
2019-03-13 20:01 ` Mike Kravetz
2019-03-13 23:55 ` Andrea Arcangeli
2019-03-14 3:32 ` Mike Kravetz
2019-03-13 17:50 ` Mike Kravetz
2019-03-15 8:26 ` Peter Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190313185230.GH25147@redhat.com \
--to=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=cracauer@cons.org \
--cc=dgilbert@redhat.com \
--cc=dplotnikov@virtuozzo.com \
--cc=gokhale2@llnl.gov \
--cc=hannes@cmpxchg.org \
--cc=hughd@google.com \
--cc=jglisse@redhat.com \
--cc=keescook@chromium.org \
--cc=kirill@shutemov.name \
--cc=kvm@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=maxime.coquelin@redhat.com \
--cc=mcfadden8@llnl.gov \
--cc=mcgrof@kernel.org \
--cc=mgorman@suse.de \
--cc=mike.kravetz@oracle.com \
--cc=pbonzini@redhat.com \
--cc=peterx@redhat.com \
--cc=rppt@linux.vnet.ibm.com \
--cc=xemul@virtuozzo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).