From ff45aea0ead9f76e2e0387b579ff0bdc71a1af74 Mon Sep 17 00:00:00 2001
From: Syrus Akbary <me@syrusakbary.com>
Date: Sat, 15 Dec 2018 10:30:53 -0800
Subject: [PATCH] [WIP] Improved memory handling (#56)

* Improved memory handling

* Fix memory accessibility

* Fix formatting
---
 src/common/mmap/unix.rs     |  1 -
 src/common/mmap/windows.rs  |  4 ++--
 src/webassembly/instance.rs |  2 +-
 src/webassembly/memory.rs   | 19 +++++++++----------
 4 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/src/common/mmap/unix.rs b/src/common/mmap/unix.rs
index cc60063f4..64071f6f0 100644
--- a/src/common/mmap/unix.rs
+++ b/src/common/mmap/unix.rs
@@ -43,7 +43,6 @@ impl Mmap {
             libc::mmap(
                 ptr::null_mut(),
                 alloc_size,
-                // libc::PROT_READ | libc::PROT_WRITE,
                 libc::PROT_NONE,
                 libc::MAP_PRIVATE | libc::MAP_ANON,
                 -1,
diff --git a/src/common/mmap/windows.rs b/src/common/mmap/windows.rs
index 6e692398d..52fe80be6 100644
--- a/src/common/mmap/windows.rs
+++ b/src/common/mmap/windows.rs
@@ -7,7 +7,7 @@ use std::ptr;
 use std::slice;
 use std::string::String;
 use winapi::um::memoryapi::{VirtualAlloc, VirtualFree};
-use winapi::um::winnt::{MEM_COMMIT, MEM_RELEASE, MEM_RESERVE, PAGE_READWRITE};
+use winapi::um::winnt::{MEM_COMMIT, MEM_RELEASE, MEM_RESERVE, PAGE_NOACCESS};
 
 use super::common::round_up_to_page_size;
 
@@ -39,7 +39,7 @@ impl Mmap {
                 ptr::null_mut(),
                 size,
                 MEM_COMMIT | MEM_RESERVE,
-                PAGE_READWRITE,
+                PAGE_NOACCESS,
             )
         };
         if !ptr.is_null() {
diff --git a/src/webassembly/instance.rs b/src/webassembly/instance.rs
index a731b1804..fdcdeefd7 100644
--- a/src/webassembly/instance.rs
+++ b/src/webassembly/instance.rs
@@ -509,7 +509,7 @@ impl Instance {
                 let mem = &mut memories[init.memory_index.index()];
                 let end_of_init = offset + init.data.len();
                 if end_of_init > mem.current_size() {
-                    let grow_pages = (end_of_init / LinearMemory::WASM_PAGE_SIZE) + 1;
+                    let grow_pages = (end_of_init / LinearMemory::PAGE_SIZE as usize) + 1;
                     mem.grow(grow_pages as u32)
                         .expect("failed to grow memory for data initializers");
                 }
diff --git a/src/webassembly/memory.rs b/src/webassembly/memory.rs
index 0c755bf34..cc69a66f2 100644
--- a/src/webassembly/memory.rs
+++ b/src/webassembly/memory.rs
@@ -35,7 +35,6 @@ pub struct LinearMemory {
 impl LinearMemory {
     pub const PAGE_SIZE: u32 = 65536;
     pub const MAX_PAGES: u32 = 65536;
-    pub const WASM_PAGE_SIZE: usize = 1 << 16; // 64 KiB
     pub const DEFAULT_HEAP_SIZE: usize = 1 << 32; // 4 GiB
     pub const DEFAULT_GUARD_SIZE: usize = 1 << 31; // 2 GiB
     pub const DEFAULT_SIZE: usize = Self::DEFAULT_HEAP_SIZE + Self::DEFAULT_GUARD_SIZE; // 6 GiB
@@ -51,18 +50,17 @@ impl LinearMemory {
             initial, maximum
         );
 
-        let offset_guard_size = LinearMemory::DEFAULT_SIZE as usize;
-        let mut mmap = Mmap::with_size(offset_guard_size).expect("Can't create mmap");
+        let mut mmap = Mmap::with_size(Self::DEFAULT_SIZE).expect("Can't create mmap");
 
         let base = mmap.as_mut_ptr();
 
+        // map initial pages as readwrite since the inital mmap is mapped as not accessible.
         if initial != 0 {
             unsafe {
                 region::protect(
-                    base as _,
+                    base,
                     initial as usize * Self::PAGE_SIZE as usize,
-                    region::Protection::Read | region::Protection::Write,
-                    // region::Protection::None,
+                    region::Protection::ReadWrite,
                 )
             }
             .expect("unable to make memory inaccessible");
@@ -82,7 +80,7 @@ impl LinearMemory {
         Self {
             mmap,
             current: initial,
-            offset_guard_size,
+            offset_guard_size: LinearMemory::DEFAULT_GUARD_SIZE,
             maximum,
         }
     }
@@ -137,15 +135,16 @@ impl LinearMemory {
         let prev_bytes = (prev_pages * Self::PAGE_SIZE) as usize;
         let new_bytes = (new_pages * Self::PAGE_SIZE) as usize;
 
+        // if new_bytes > self.mmap.len() - self.offset_guard_size {
         unsafe {
             region::protect(
-                self.mmap.as_mut_ptr().add(prev_bytes) as _,
+                self.mmap.as_ptr().add(prev_bytes) as _,
                 new_bytes - prev_bytes,
-                region::Protection::Read | region::Protection::Write,
-                // region::Protection::None,
+                region::Protection::ReadWrite,
             )
         }
         .expect("unable to make memory inaccessible");
+        // };
         // if new_bytes > self.mmap.len() - self.offset_guard_size {
         //     // If we have no maximum, this is a "dynamic" heap, and it's allowed to move.
         //     assert!(self.maximum.is_none());