x86: Add ENDBR at function entries
Intel Control-flow Enforcement Technology (CET):
https://software.intel.com/en-us/articles/intel-sdm
contains shadow stack (SHSTK) and indirect branch tracking (IBT). When IBT is enabled, all indirect branch targets must start with ENDBR instruction which is a NOP on non-CET processors.
Closes: #2538 (closed)
Reviewed-by: Dave Airlie <airlied@redhat.com>
Acked-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>