From: Alexei Starovoitov <alexei.starovoitov@gmail.com> To: Thomas Gleixner <tglx@linutronix.de> Cc: Jordan Glover <Golden_Miller83@protonmail.ch>, Andy Lutomirski <luto@kernel.org>, Daniel Colascione <dancol@google.com>, Song Liu <songliubraving@fb.com>, Kees Cook <keescook@chromium.org>, Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Kernel Team <Kernel-team@fb.com>, Lorenz Bauer <lmb@cloudflare.com>, Jann Horn <jannh@google.com>, Greg KH <gregkh@linuxfoundation.org>, Linux API <linux-api@vger.kernel.org>, LSM List <linux-security-module@vger.kernel.org> Subject: Re: [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Date: Sat, 17 Aug 2019 08:02:47 -0700 Message-ID: <20190817150245.xxzxqjpvgqsxmloe@ast-mbp> (raw) In-Reply-To: <alpine.DEB.2.21.1908162211270.1923@nanos.tec.linutronix.de> On Fri, Aug 16, 2019 at 10:28:29PM +0200, Thomas Gleixner wrote: > Alexei, > > On Fri, 16 Aug 2019, Alexei Starovoitov wrote: > > It's both of the above when 'systemd' is not taken literally. > > To earlier Thomas's point: the use case is not only about systemd. > > There are other containers management systems. > > <SNIP> > > > These daemons need to drop privileges to make the system safer == less > > prone to corruption due to bugs in themselves. Not necessary security > > bugs. > > Let's take a step back. > > While real usecases are helpful to understand a design decision, the design > needs to be usecase independent. > > The kernel provides mechanisms, not policies. My impression of this whole > discussion is that it is policy driven. That's the wrong approach. not sure what you mean by 'policy driven'. Proposed CAP_BPF is a policy? My desire to do kernel.unprivileged_bpf_disabled=1 is driven by text in Documentation/x86/mds.rst which says: "There is one exception, which is untrusted BPF. The functionality of untrusted BPF is limited, but it needs to be thoroughly investigated whether it can be used to create such a construct." commit 6a9e52927251 ("x86/speculation/mds: Add mds_clear_cpu_buffers()") Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Borislav Petkov <bp@suse.de> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Jon Masters <jcm@redhat.com> Tested-by: Jon Masters <jcm@redhat.com> The way I read this text: - there is a concern that mds is exploitable via bpf - there is a desire to investigate to address this concern I'm committed to help with the investigation. In the mean time I propose a path to do kernel.unprivileged_bpf_disabled=1 which is CAP_BPF. Can kernel.unprivileged_bpf_disabled=1 be used now? Yes, but it will weaken overall system security because things that use unpriv to load bpf and CAP_NET_ADMIN to attach bpf would need to move to stronger CAP_SYS_ADMIN. With CAP_BPF both load and attach would happen under CAP_BPF instead of CAP_SYS_ADMIN. > So let's look at the mechanisms which we have at hand: > > 1) Capabilities > > 2) SUID and dropping priviledges > > 3) Seccomp and LSM > > Now the real interesting questions are: > > A) What kind of restrictions does BPF allow? Is it a binary on/off or is > there a more finegrained control of BPF functionality? > > TBH, I can't tell. > > B) Depending on the answer to #A what is the control possibility for > #1/#2/#3 ? Can any of the mechanisms 1/2/3 address the concern in mds.rst? I believe Andy wants to expand the attack surface when kernel.unprivileged_bpf_disabled=0 Before that happens I'd like the community to work on addressing the text above.
next prev parent reply index Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <20190627201923.2589391-1-songliubraving@fb.com> [not found] ` <20190627201923.2589391-2-songliubraving@fb.com> [not found] ` <21894f45-70d8-dfca-8c02-044f776c5e05@kernel.org> [not found] ` <3C595328-3ABE-4421-9772-8D41094A4F57@fb.com> [not found] ` <CALCETrWBnH4Q43POU8cQ7YMjb9LioK28FDEQf7aHZbdf1eBZWg@mail.gmail.com> [not found] ` <0DE7F23E-9CD2-4F03-82B5-835506B59056@fb.com> [not found] ` <CALCETrWBWbNFJvsTCeUchu3BZJ3SH3dvtXLUB2EhnPrzFfsLNA@mail.gmail.com> [not found] ` <201907021115.DCD56BBABB@keescook> [not found] ` <CALCETrXTta26CTtEDnzvtd03-WOGdXcnsAogP8JjLkcj4-mHvg@mail.gmail.com> [not found] ` <4A7A225A-6C23-4C0F-9A95-7C6C56B281ED@fb.com> [not found] ` <CALCETrX2bMnwC6_t4b_G-hzJSfMPrkK4YKs5ebcecv2LJ0rt3w@mail.gmail.com> [not found] ` <514D5453-0AEE-420F-AEB6-3F4F58C62E7E@fb.com> [not found] ` <1DE886F3-3982-45DE-B545-67AD6A4871AB@amacapital.net> [not found] ` <7F51F8B8-CF4C-4D82-AAE1-F0F28951DB7F@fb.com> [not found] ` <77354A95-4107-41A7-8936-D144F01C3CA4@fb.com> [not found] ` <369476A8-4CE1-43DA-9239-06437C0384C7@fb.com> 2019-07-30 20:24 ` Andy Lutomirski 2019-07-31 8:10 ` Song Liu 2019-07-31 19:09 ` Andy Lutomirski 2019-08-02 7:21 ` Song Liu 2019-08-04 22:16 ` Andy Lutomirski 2019-08-05 0:08 ` Andy Lutomirski 2019-08-05 5:47 ` Andy Lutomirski 2019-08-05 7:36 ` Song Liu 2019-08-05 17:23 ` Andy Lutomirski 2019-08-05 19:21 ` Alexei Starovoitov 2019-08-05 21:25 ` Andy Lutomirski 2019-08-05 22:21 ` Andy Lutomirski 2019-08-06 1:11 ` Alexei Starovoitov 2019-08-07 5:24 ` Andy Lutomirski 2019-08-07 9:03 ` Lorenz Bauer 2019-08-07 13:52 ` Andy Lutomirski 2019-08-13 21:58 ` Alexei Starovoitov 2019-08-13 22:26 ` Daniel Colascione 2019-08-13 23:24 ` Andy Lutomirski 2019-08-13 23:06 ` Andy Lutomirski 2019-08-14 0:57 ` Alexei Starovoitov 2019-08-14 17:51 ` Andy Lutomirski 2019-08-14 22:05 ` Alexei Starovoitov 2019-08-14 22:30 ` Andy Lutomirski 2019-08-14 23:33 ` Alexei Starovoitov 2019-08-14 23:59 ` Andy Lutomirski 2019-08-15 0:36 ` Alexei Starovoitov 2019-08-15 11:24 ` Jordan Glover 2019-08-15 17:28 ` Alexei Starovoitov 2019-08-15 18:36 ` Andy Lutomirski 2019-08-15 23:08 ` Alexei Starovoitov 2019-08-16 9:34 ` Jordan Glover 2019-08-16 9:59 ` Thomas Gleixner 2019-08-16 11:33 ` Jordan Glover 2019-08-16 19:52 ` Alexei Starovoitov 2019-08-16 20:28 ` Thomas Gleixner 2019-08-17 15:02 ` Alexei Starovoitov [this message] 2019-08-17 15:44 ` Andy Lutomirski 2019-08-19 9:15 ` Thomas Gleixner 2019-08-19 17:27 ` Alexei Starovoitov 2019-08-19 17:38 ` Andy Lutomirski 2019-08-15 18:43 ` Jordan Glover 2019-08-15 19:46 ` Kees Cook 2019-08-15 23:46 ` Alexei Starovoitov 2019-08-16 0:54 ` Andy Lutomirski 2019-08-16 5:56 ` Song Liu 2019-08-16 21:45 ` Alexei Starovoitov 2019-08-16 22:22 ` Christian Brauner 2019-08-17 15:08 ` Alexei Starovoitov 2019-08-17 15:16 ` Christian Brauner 2019-08-17 15:36 ` Alexei Starovoitov 2019-08-17 15:42 ` Christian Brauner 2019-08-22 14:17 ` Daniel Borkmann 2019-08-22 15:16 ` Andy Lutomirski 2019-08-22 15:17 ` RFC: very rough draft of a bpf permission model Andy Lutomirski 2019-08-22 23:26 ` Alexei Starovoitov 2019-08-23 23:09 ` Andy Lutomirski 2019-08-26 22:36 ` Alexei Starovoitov 2019-08-27 0:05 ` Andy Lutomirski 2019-08-27 0:34 ` Alexei Starovoitov 2019-08-22 22:48 ` [PATCH v2 bpf-next 1/4] bpf: unprivileged BPF access via /dev/bpf Alexei Starovoitov
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