EPT handling improvements (closes wbenny#6)

- Use 2MB pages by default
- Cover first 512GB of memory with them
- Implement splitting of large pages
- Implemnt complementary joining (merging) back into large pages

README.md

@@ -48,8 +48,10 @@ read and navigate through 5000 pages with browser's built-in PDF reader.
 
 ### Features
 
-- EPT with identity mapping **with usage of 2MB pages** for device physical memory ranges (see [ept.cpp](src/hvpp/hvpp/ept.cpp))
-  and any memory in first 4GB range which is not backed by actual physical memory.
+- EPT with identity mapping **with usage of 2MB pages** for the first 512GB of physical memory (see [ept.cpp](src/hvpp/hvpp/ept.cpp)).
+  This results in faster translations of the memory. It also means splitting particular 2MB pages into 4kb pages might
+  be desired if EPT hooking is required. This process is actually not complicated at all and this repository includes
+  example on how to achieve that.
 - Simple pass-through VM-exit handler, which can handle:
   - exceptions or [NMIs][nmi]
   - `CPUID`, `(WB)INVD`, `INVLPG`, `RDTSC(P)`, `MOV CR`, `MOV DR`, `IN/OUT`, `RDMSR`, `WRMSR`, `SGDT`, `SIDT`, `LGDT`,

src/hvpp/custom_vmexit.cpp

@@ -115,7 +115,12 @@ void custom_vmexit_handler::handle_execute_vmcall(vcpu_t& vp) noexcept
       hvpp_trace("vmcall (hook) EXEC: 0x%p READ: 0x%p", data.page_exec.value(), data.page_read.value());
 
       //
-      // Set execute-only access.
+      // Split the 2MB page where the code we want to hook resides.
+      //
+      vp.ept().split_2mb_to_4kb(data.page_exec & ept_pd_t::mask, data.page_exec & ept_pd_t::mask);
+
+      //
+      // Set execute-only access on the page we want to hook.
       //
       vp.ept().map_4kb(data.page_exec, data.page_exec, epte_t::access_type::execute);
 
@@ -130,9 +135,10 @@ void custom_vmexit_handler::handle_execute_vmcall(vcpu_t& vp) noexcept
       hvpp_trace("vmcall (unhook)");
 
       //
-      // Set back read-write-execute access.
+      // Merge the 4kb pages back to the original 2MB large page. Note that this
+      // will also automatically set the access rights to read_write_execute.
       //
-      vp.ept().map_4kb(data.page_exec, data.page_exec, epte_t::access_type::read_write_execute);
+      vp.ept().join_4kb_to_2mb(data.page_exec & ept_pd_t::mask, data.page_exec & ept_pd_t::mask);
 
       //
       // We've changed EPT structure - mappings derived from EPT need to be

src/hvpp/hvpp.vcxproj

@@ -143,6 +143,7 @@
     <ClInclude Include="ia32\msr\mtrr.h" />
     <ClInclude Include="ia32\msr\vmx.h" />
     <ClInclude Include="ia32\mtrr.h" />
+    <ClInclude Include="ia32\paging.h" />
     <ClInclude Include="ia32\vmx.h" />
     <ClInclude Include="ia32\vmx\exception_bitmap.h" />
     <ClInclude Include="ia32\vmx\instruction_info.h" />

src/hvpp/hvpp.vcxproj.filters

@@ -266,6 +266,9 @@
     <ClInclude Include="ia32\cpuid\cpuid_eax_01.h">
       <Filter>Header Files\ia32\cpuid</Filter>
     </ClInclude>
+    <ClInclude Include="ia32\paging.h">
+      <Filter>Header Files\ia32</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <MASM Include="ia32\context.asm">