commit 1bd36d694dba00d92651fcd2340e91d5a74efb03
author Régis Crelier <regis@google.com> Tue Mar 12 23:42:35 2019 +0000
committer commit-bot@chromium.org <commit-bot@chromium.org> Tue Mar 12 23:42:35 2019 +0000
tree 9b53a547b6e35b04513dc150926ff209e5bcb924
parent 0bd674c3748eaa39adf7d0f65ae9620dc57d5876

[vm runtime] Dynamically disable dual mapping of code on some platforms.

Until a better solution is found, disable dual mapping of code on docker
containers that fail setting exec permissions on dual mappings.

Change-Id: Ic7477e1ef70ae0ea4d0187284702d5a3ee594edf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/96668
Commit-Queue: Régis Crelier <regis@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>
Auto-Submit: Régis Crelier <regis@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>

runtime/vm/virtual_memory_posix.cc

diff --git a/runtime/vm/virtual_memory_posix.cc b/runtime/vm/virtual_memory_posix.cc
index 8291ff0..bf22734 100644
--- a/runtime/vm/virtual_memory_posix.cc
+++ b/runtime/vm/virtual_memory_posix.cc
@@ -43,6 +43,23 @@
 
 #if defined(DUAL_MAPPING_SUPPORTED)
   shm_unlink(DART_SHM_NAME);  // Could be left over from a previous crash.
+
+  // Detect dual mapping exec permission limitation on some platforms,
+  // such as on docker containers, and disable dual mapping in this case.
+  if (FLAG_dual_map_code) {
+    intptr_t size = page_size_;
+    intptr_t alignment = 256 * 1024;  // e.g. heap page size.
+    VirtualMemory* vm = AllocateAligned(size, alignment, true, NULL);
+    void* region = reinterpret_cast<void*>(vm->region_.start());
+    void* alias = reinterpret_cast<void*>(vm->alias_.start());
+    if (region == alias ||
+        mprotect(region, size, PROT_READ) != 0 ||  // Remove PROT_WRITE.
+        mprotect(alias, size, PROT_READ | PROT_EXEC) != 0) {  // Add PROT_EXEC.
+      LOG_INFO("disabling dual mapping of code\n");
+      FLAG_dual_map_code = false;
+    }
+    delete vm;
+  }
 #endif                        // defined(DUAL_MAPPING_SUPPORTED)
 }