bpf: prevent speculative execution in eBPF interpreter

bpf: prevent speculative execution in eBPF interpreter

This adds an observable speculation barrier before LD_IMM_DW and
LDX_MEM_B/H/W/DW eBPF instructions during eBPF program
execution in order to prevent speculative execution on out
of bound BFP_MAP array indexes. This way an arbitary kernel
memory is not exposed through side channel attacks.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Orabug: 27340445
CVE: CVE-2017-5753

Signed-off-by: Chuck Anderson <chuck.anderson@oracle.com>
Conflicts:
	kernel/bpf/core.c code base differences

Reviewed-by: John Haxby <john.haxby@oracle.com>
Signed-off-by: Kirtikar Kashyap <kirtikar.kashyap@oracle.com>