[GIT PULL] Kernel lockdown for secure boot

Alexei Starovoitov alexei.starovoitov at gmail.com
Wed Apr 4 02:34:25 UTC 2018

On Tue, Apr 3, 2018 at 9:26 AM, Andy Lutomirski <luto at kernel.org> wrote:
> On Tue, Apr 3, 2018 at 8:41 AM, Alexei Starovoitov
> <alexei.starovoitov at gmail.com> wrote:
>> On Tue, Apr 03, 2018 at 08:11:07AM -0700, Andy Lutomirski wrote:
>>> >
>>> >> "bpf: Restrict kernel image access functions when the kernel is locked down":
>>> >> This patch just sucks in general.
>>> >
>>> > Yes - but that's what Alexei Starovoitov specified.  bpf kind of sucks since
>>> > it gives you unrestricted access to the kernel.
>>> bpf, in certain contexts, gives you unrestricted access to *reading*
>>> kernel memory.  bpf should, under no circumstances, let you write to
>>> the kernel unless you're using fault injection or similar.
>>> I'm surprised that Alexei acked this patch.  If something like XDP or
>>> bpfilter starts becoming widely used, this patch will require a lot of
>>> reworking to avoid breaking standard distros.
>> my understanding was that this lockdown set attemps to disallow _reads_
>> of kernel memory from anything, so first version of patch was adding
>> run-time checks for bpf_probe_read() which is no-go
>> and without this helper the bpf for tracing is losing a lot of its power,
>> so the easiest is to disable it all.
> Fair enough.

Actually looking at the patch again:

If the only thing that folks are paranoid about is reading
arbitrary kernel memory with bpf_probe_read() helper
then preferred patch would be to disable it during verification
when in lockdown mode.
No run-time overhead and android folks will be happy
that lockdown doesn't break their work.
They converted out-of-tree networking accounting
module and corresponding user daemon to use bpf:
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