From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Peter Xu <peterx@redhat.com>
Cc: linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
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 Kravetz <mike.kravetz@oracle.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Kees Cook <keescook@chromium.org>, Mel Gorman <mgorman@suse.de>,
linux-fsdevel@vger.kernel.org,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-api@vger.kernel.org
Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users
Date: Tue, 12 Mar 2019 10:49:51 +0300 [thread overview]
Message-ID: <20190312074951.i2md3npcjcceywqj@kshutemo-mobl1> (raw)
In-Reply-To: <20190311093701.15734-1-peterx@redhat.com>
On Mon, Mar 11, 2019 at 05:36:58PM +0800, Peter Xu wrote:
> Hi,
>
> (The idea comes from Andrea, and following discussions with Mike and
> other people)
>
> This patchset introduces a new sysctl flag to allow the admin to
> forbid users from using userfaultfd:
>
> $ cat /proc/sys/vm/unprivileged_userfaultfd
> [disabled] enabled kvm
CC linux-api@
This is unusual way to return current value for sysctl. Does it work fine
with sysctl tool?
Have you considered to place the switch into /sys/kernel/mm instead?
I doubt it's the last tunable for userfaultfd. Maybe we should have an
directory for it under /sys/kernel/mm?
> - When set to "disabled", all unprivileged users are forbidden to
> use userfaultfd syscalls.
>
> - When set to "enabled", all users are allowed to use userfaultfd
> syscalls.
>
> - When set to "kvm", all unprivileged users are forbidden to use the
> userfaultfd syscalls, except the user who has permission to open
> /dev/kvm.
>
> This new flag can add one more layer of security to reduce the attack
> surface of the kernel by abusing userfaultfd. Here we grant the
> thread userfaultfd permission by checking against CAP_SYS_PTRACE
> capability. By default, the value is "disabled" which is the most
> strict policy. Distributions can have their own perferred value.
>
> The "kvm" entry is a bit special here only to make sure that existing
> users like QEMU/KVM won't break by this newly introduced flag. What
> we need to do is simply set the "unprivileged_userfaultfd" flag to
> "kvm" here to automatically grant userfaultfd permission for processes
> like QEMU/KVM without extra code to tweak these flags in the admin
> code.
>
> Patch 1: The interface patch to introduce the flag
>
> Patch 2: The KVM related changes to detect opening of /dev/kvm
>
> Patch 3: Apply the flag to userfaultfd syscalls
>
> All comments would be greatly welcomed. Thanks,
>
> Peter Xu (3):
> userfaultfd/sysctl: introduce unprivileged_userfaultfd
> kvm/mm: introduce MMF_USERFAULTFD_ALLOW flag
> userfaultfd: apply unprivileged_userfaultfd check
>
> fs/userfaultfd.c | 121 +++++++++++++++++++++++++++++++++
> include/linux/sched/coredump.h | 1 +
> include/linux/userfaultfd_k.h | 5 ++
> init/Kconfig | 11 +++
> kernel/sysctl.c | 11 +++
> virt/kvm/kvm_main.c | 7 ++
> 6 files changed, 156 insertions(+)
>
> --
> 2.17.1
>
--
Kirill A. Shutemov
next prev parent reply other threads:[~2019-03-12 7:49 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 [this message]
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
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
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