Add #guard_page and #crypto_key

Author: didactic-drunk

README.md

@@ -32,7 +32,7 @@ Mmap::Region.open(16384) do |mmap|
   mmap.to_slice
 
 
-  # Not a Slice
+  # SubRegions reference the original Mmap::Region, tracking the offset if resized
   rw_region = mmap[0, 4096]
   # Do something with the first 4k
   rw_region.to_slice
@@ -45,7 +45,7 @@ Mmap::Region.open(16384) do |mmap|
 
   # Create a guard page
   guard_region = mmap[12288, 4096]
-  guard_region.noaccess
+  guard_region.guard_page
   # Crashes program if accessed
   guard_region.to_slice[0] = 0_u8
 end

spec/mmap_spec.cr

@@ -1,15 +1,20 @@
 require "./spec_helper"
 require "../src/mmap"
 
+# Check restricting type to Module
+private def can_to_slice(mmap : Mmap) : Bytes
+  mmap.to_slice
+end
+
 describe Mmap do
   it "maps anon memory" do
     initial_size = 2048
     Mmap::Region.open(initial_size) do |mmap|
-      mmap.to_slice[7] = 7_u8
+      can_to_slice(mmap)[7] = 7_u8
       sub1 = mmap[5, 10]
-      sub1.to_slice[2].should eq 7_u8
+      can_to_slice(sub1)[2].should eq 7_u8
       sub2 = sub1[2, 1]
-      sub2.to_slice[0].should eq 7_u8
+      can_to_slice(sub2)[0].should eq 7_u8
 
       expect_raises IndexError do
         mmap[initial_size, 1]
@@ -53,6 +58,21 @@ describe Mmap do
   pending "msync" do
   end
 
+  it "guard_page" do
+    Mmap::Region.open(8192) do |mmap|
+      mmap.guard_page
+# TODO: trap
+#      mmap.to_slice[0] = 1_u8
+    end
+  end
+
+  it "guard_page" do
+    Mmap::Region.open(8192) do |mmap|
+      mmap.crypto_key
+      mmap.to_slice[0] = 1_u8
+    end
+  end
+
   it "mlock" do
     Mmap::Region.open(8192) do |mmap|
       mmap.mlock

src/mmap/mmap.cr

@@ -1,6 +1,8 @@
 require "./*"
 
 module Mmap
+  PAGE_SIZE = LibC.sysconf LibC::SC_PAGESIZE
+
   class Error < Exception
     class Closed < Error
     end
@@ -34,6 +36,9 @@ module Mmap
     # Nonblock = LibC::MAP_NONBLOCK # Linux only (requires POPULATE) - currently turns POPULATE in to noop
     # Possibly same as Linux POPULATE & NONBLOCK but functional
     # PreFaultRead = LibC::MAP_PREFAULT_READ # BSD only
+    #    CryptoKey = LibC::MAP_DONTDUMP | LibC::MAP_DONTFORK # Fails on Linux
+    CryptoKey = LibC::MAP_DONTDUMP
+    GuardPage = LibC::MAP_DONTDUMP
   end
 
   def self.open(*args)
@@ -87,6 +92,15 @@ module Mmap
     raise RuntimeError.from_errno("munlock") if r != 0
   end
 
+  def crypto_key : Nil
+    madvise Flags::CryptoKey
+  end
+
+  def guard_page : Nil
+    madvise Flags::GuardPage
+    noaccess
+  end
+
   def to_slice : Bytes
     Slice.new to_unsafe, @size
   end