[heap] Add a read-only permission

Add a new permission kRead to PageAllocator::Permission and
OS::MemoryPermission and implement it in platform-*.

Not used yet, because it needs corresponding changes in chromium.

Bug: v8:7464
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I9f84251eff593536cbcc1cde04641d696c79d65c
Reviewed-on: https://chromium-review.googlesource.com/1006756Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52636}

include/v8-platform.h

@@ -206,6 +206,7 @@ class PageAllocator {
    */
   enum Permission {
     kNoAccess,
+    kRead,
     kReadWrite,
     // TODO(hpayer): Remove this flag. Memory should never be rwx.
     kReadWriteExecute,

src/base/platform/platform-cygwin.cc

@@ -34,6 +34,8 @@ DWORD GetProtectionFromMemoryPermission(OS::MemoryPermission access) {
   switch (access) {
     case OS::MemoryPermission::kNoAccess:
       return PAGE_NOACCESS;
+    case OS::MemoryPermission::kRead:
+      return PAGE_READONLY;
     case OS::MemoryPermission::kReadWrite:
       return PAGE_READWRITE;
     case OS::MemoryPermission::kReadWriteExecute:

src/base/platform/platform-fuchsia.cc

@@ -19,6 +19,8 @@ uint32_t GetProtectionFromMemoryPermission(OS::MemoryPermission access) {
   switch (access) {
     case OS::MemoryPermission::kNoAccess:
       return 0;  // no permissions
+    case OS::MemoryPermission::kRead:
+      return ZX_VM_FLAG_PERM_READ;
     case OS::MemoryPermission::kReadWrite:
       return ZX_VM_FLAG_PERM_READ | ZX_VM_FLAG_PERM_WRITE;
     case OS::MemoryPermission::kReadWriteExecute:

src/base/platform/platform-posix.cc

@@ -112,6 +112,8 @@ int GetProtectionFromMemoryPermission(OS::MemoryPermission access) {
   switch (access) {
     case OS::MemoryPermission::kNoAccess:
       return PROT_NONE;
+    case OS::MemoryPermission::kRead:
+      return PROT_READ;
     case OS::MemoryPermission::kReadWrite:
       return PROT_READ | PROT_WRITE;
     case OS::MemoryPermission::kReadWriteExecute:

src/base/platform/platform-win32.cc

@@ -758,6 +758,8 @@ DWORD GetProtectionFromMemoryPermission(OS::MemoryPermission access) {
   switch (access) {
     case OS::MemoryPermission::kNoAccess:
       return PAGE_NOACCESS;
+    case OS::MemoryPermission::kRead:
+      return PAGE_READONLY;
     case OS::MemoryPermission::kReadWrite:
       return PAGE_READWRITE;
     case OS::MemoryPermission::kReadWriteExecute:

src/base/platform/platform.h

@@ -159,6 +159,7 @@ class V8_BASE_EXPORT OS {
   // v8::PageAllocator.
   enum class MemoryPermission {
     kNoAccess,
+    kRead,
     kReadWrite,
     // TODO(hpayer): Remove this flag. Memory should never be rwx.
     kReadWriteExecute,

test/unittests/allocation-unittest.cc

@@ -110,6 +110,7 @@ sigjmp_buf MemoryAllocationPermissionsTest::continuation_;
 
 TEST_F(MemoryAllocationPermissionsTest, DoTest) {
   TestPermissions(PageAllocator::Permission::kNoAccess, false, false);
+  TestPermissions(PageAllocator::Permission::kRead, true, false);
   TestPermissions(PageAllocator::Permission::kReadWrite, true, true);
   TestPermissions(PageAllocator::Permission::kReadWriteExecute, true, true);
   TestPermissions(PageAllocator::Permission::kReadExecute, true, false);