linux-kernel - Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API.

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Message-Id: <20191025201242.GA8710@linux.ibm.com>
Date:   Fri, 25 Oct 2019 23:12:43 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Andrea Arcangeli <aarcange@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>, Jann Horn <jannh@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Nick Kralevich <nnk@...gle.com>,
        Nosh Minwalla <nosh@...gle.com>,
        Tim Murray <timmurray@...gle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Linux API <linux-api@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/7] Add a UFFD_SECURE flag to the userfaultfd API.

Hi,

On Thu, Oct 24, 2019 at 11:10:54AM -0400, Andrea Arcangeli wrote:
> Hello,
> 
> On Thu, Oct 24, 2019 at 12:02:59PM +0300, Mike Rapoport wrote:
> > That's no the reason that UFFD_FEATURE_EVENT_FORK does not show up in
> > Debian code search, CRIU simply is not there. Debian packages CRIU only in
> > experimental and I believe that's not indexed by the code search.
> > 
> > As for the limitations, the races were fixed, I just forgot to update the
> > wiki. As for the supported memory types and COW pages, these only affect
> > efficiency of post-copy, but not the correctness.
> 
> That's what I was hoping for. If the wiki information is stale and
> there are no races it is totally plausible that it's being actively
> used in production so we need to fix the kernel bug. I was just
> checking because I wasn't sure anymore of the status after I read the
> wiki.
> 
> If the CRIU initialization code that issues the uffd syscall runs as
> global root the ABI breaking permission check from Andy sounds the
> simplest for a short term fix, because it will be unnoticed by any
> production usage with CIRU --lazy-pages.
 
In general, criu can run as non-root, but such use of criu has limitations,
so allowing criu --lazy-pages only for root sounds reasonable as a short
term solution.

> Then later we could add a UFFD_FEATURE_EVENT_FORK2 that will not
> require root permission.

Agree.

> Thanks,
> Andrea
> 

-- 
Sincerely yours,
Mike.