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Date:   Tue, 26 Mar 2019 01:00:29 +0100
From:   Daniel Borkmann <>
To:     Stephen Hemminger <>,
        Matthew Garrett <>
        Alexei Starovoitov <>,, Chun-Yi Lee <>,
        Kees Cook <>,
        Andy Lutomirski <>,
        Will Drewry <>
Subject: Re: [PATCH 23/27] bpf: Restrict kernel image access functions when
 the kernel is locked down

On 03/26/2019 12:42 AM, Stephen Hemminger wrote:
> On Mon, 25 Mar 2019 15:09:50 -0700
> Matthew Garrett <> wrote:
>> From: David Howells <>
>> There are some bpf functions can be used to read kernel memory:
>> bpf_probe_read, bpf_probe_write_user and bpf_trace_printk.  These allow
>> private keys in kernel memory (e.g. the hibernation image signing key) to
>> be read by an eBPF program and kernel memory to be altered without
>> restriction.

I'm not sure where 'kernel memory to be altered without restriction' comes
from, but it's definitely a wrong statement.

>> Completely prohibit the use of BPF when the kernel is locked down.

In which scenarios will the lock-down mode be used? Mostly niche? I'm asking
as this would otherwise break a lot of existing stuff ... I'd prefer you find
a better solution to this than this straight -EPERM rejection.

>> Suggested-by: Alexei Starovoitov <>
>> Signed-off-by: David Howells <>
>> cc:
>> cc: Chun-Yi Lee <>
>> cc: Alexei Starovoitov <>
>> Cc: Daniel Borkmann <>
>> Signed-off-by: Matthew Garrett <>
> Wouldn't this mean that Seccomp won't work in locked down mode?

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