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[209.85.217.52]) by smtp.gmail.com with ESMTPSA id j28sm484466vsl.10.2019.03.15.09.09.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 15 Mar 2019 09:09:57 -0700 (PDT) Received: by mail-vs1-f52.google.com with SMTP id b8so5692991vsq.11 for ; Fri, 15 Mar 2019 09:09:57 -0700 (PDT) X-Received: by 2002:a67:fa45:: with SMTP id j5mr2431791vsq.48.1552666196638; Fri, 15 Mar 2019 09:09:56 -0700 (PDT) MIME-Version: 1.0 References: <20190311093701.15734-1-peterx@redhat.com> <58e63635-fc1b-cb53-a4d1-237e6b8b7236@oracle.com> <20190313060023.GD2433@xz-x1> <3714d120-64e3-702e-6eef-4ef253bdb66d@redhat.com> <20190313185230.GH25147@redhat.com> <1934896481.7779933.1552504348591.JavaMail.zimbra@redhat.com> <20190313234458.GJ25147@redhat.com> <298b9469-abd2-b02b-5c71-529b8976a46c@redhat.com> <20190314161630.GS25147@redhat.com> In-Reply-To: <20190314161630.GS25147@redhat.com> From: Kees Cook Date: Fri, 15 Mar 2019 09:09:45 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 0/3] userfaultfd: allow to forbid unprivileged users To: Andrea Arcangeli Cc: Paolo Bonzini , Peter Xu , Mike Kravetz , LKML , Hugh Dickins , Luis Chamberlain , Maxime Coquelin , KVM , Jerome Glisse , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Denis Plotnikov , Linux-MM , Marty McFadden , Maya Gokhale , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "linux-fsdevel@vger.kernel.org" , "Dr . David Alan Gilbert" , Andrew Morton Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 14, 2019 at 9:16 AM Andrea Arcangeli wrote: > So this will be for who's paranoid and prefers to disable userfaultfd > as a whole as an hardening feature like the bpf sysctl allows: it will > allow to block uffd syscall without having to rebuild the kernel with > CONFIG_USERFAULTFD=n in environments where seccomp cannot be easily > enabled (i.e. without requiring userland changes). > > That's very fine with me, but then it wasn't me complaining in the > first place. Kees? I'm fine with a boolean. I just wanted to find a way to disable at runtime (so distro users had it available to them). -- Kees Cook