seccomp: Limit mmap and mprotect arg2.

We do not want to allow writable executable memory.

BUG=b:172212144
TEST=CQ passes

Change-Id: Ia1ed9ddcb72b3dc96f6a36442f17be538ac252fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/touch_updater/+/3942413
Reviewed-by: Harry Cutts <hcutts@chromium.org>
Tested-by: Allen Webb <allenwebb@google.com>
Commit-Queue: Allen Webb <allenwebb@google.com>
8 files changed