Hi Alexei, Thanks for your review!
On Thu, Oct 19, 2017 at 03:18:30PM -0700, Alexei Starovoitov wrote: > On Thu, Oct 19, 2017 at 03:52:49PM +0100, David Howells wrote: > > From: Chun-Yi Lee <j...@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 <j...@suse.com> > > Signed-off-by: David Howells <dhowe...@redhat.com> > > cc: net...@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 dc498b605d5d..35e85a3fdb37 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("BPF")) { > > + memset(dst, 0, size); > > + return -EPERM; > > + } > > That doesn't help the lockdown purpose. > If you don't trust the root the only way to prevent bpf read > memory is to disable the whole thing. Not totally untrust root, I don't want that root reads arbitrary memory address through bpf. Is it not enough to lock down bpf_probe_read, bpf_probe_write_user and bpf_trace_printk? > Have a single check in sys_bpf() to disallow everything if > kernel_is_locked_down() > and don't add overhead to critical path like bpf_probe_read(). > Yes, it give overhead to bpf_probe_read but it prevents arbitrary memory read. Another idea is signing bpf bytecode then verifying signture when loading to kernel. Thanks a lot! Joey Lee -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html