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    SubjectRe: [PATCH 20/24] bpf: Restrict kernel image access functions when the kernel is locked down
    On Wed, Apr 05, 2017 at 09:17:25PM +0100, David Howells wrote:
    > From: Chun-Yi Lee <jlee@suse.com>
    >
    > 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. Prohibit those functions when the kernel is
    > locked down.
    >
    > Signed-off-by: Chun-Yi Lee <jlee@suse.com>
    > Signed-off-by: David Howells <dhowells@redhat.com>
    > cc: netdev@vger.kernel.org
    > ---
    >
    > kernel/trace/bpf_trace.c | 11 +++++++++++
    > 1 file changed, 11 insertions(+)
    >
    > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
    > index cee9802cf3e0..7fde851f207b 100644
    > --- a/kernel/trace/bpf_trace.c
    > +++ b/kernel/trace/bpf_trace.c
    > @@ -65,6 +65,11 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
    > {
    > int ret;
    >
    > + if (kernel_is_locked_down()) {
    > + memset(dst, 0, size);
    > + return -EPERM;
    > + }

    this will obviously break the program. How about disabling loading tracing
    programs during the lockdown completely?

    Also is there a description of what this lockdown trying to accomplish?
    The cover letter is scarce in details.

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