kprobes/x86: Fix to set RWX bits correctly before releasing trampoline

kprobes/x86: Fix to set RWX bits correctly before releasing trampoline

commit c93f5cf571e7795f97d49ef51b766cf25e328545 upstream.

Fix kprobes to set(recover) RWX bits correctly on trampoline
buffer before releasing it. Releasing readonly page to
module_memfree() crash the kernel.

Without this fix, if kprobes user register a bunch of kprobes
in function body (since kprobes on function entry usually
use ftrace) and unregister it, kernel hits a BUG and crash.

Link: http://lkml.kernel.org/r/149570868652.3518.14120169373590420503.stgit@devbox
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: d0381c81c2f7 ("kprobes/x86: Set kprobes pages read-only")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>