3 files changed, 16 insertions, 0 deletions
diff --git a/Kernel/VM/MemoryManager.cpp b/Kernel/VM/MemoryManager.cpp
index dcfb041828..540081d26c 100644
--- a/Kernel/VM/MemoryManager.cpp
+++ b/Kernel/VM/MemoryManager.cpp
@@ -479,6 +479,12 @@ void MemoryManager::enter_process_paging_scope(Process& process)
 {
     ASSERT(current);
     InterruptDisabler disabler;
+
+    // NOTE: To prevent triple-faulting here, we have to ensure that the current stack
+    //       is accessible to the incoming page directory. We achieve this by forcing
+    //       an update of the kernel VM mappings in the entered scope's page directory.
+    process.page_directory().update_kernel_mappings();
+
     current->tss().cr3 = process.page_directory().cr3();
     asm volatile("movl %%eax, %%cr3" ::"a"(process.page_directory().cr3())
                  : "memory");
diff --git a/Kernel/VM/PageDirectory.cpp b/Kernel/VM/PageDirectory.cpp
index 3533d6cfa9..9cc949857a 100644
--- a/Kernel/VM/PageDirectory.cpp
+++ b/Kernel/VM/PageDirectory.cpp
@@ -57,3 +57,11 @@ void PageDirectory::flush(VirtualAddress vaddr)
     if (this == &MM.kernel_page_directory() || &current->process().page_directory() == this)
         MM.flush_tlb(vaddr);
 }
+
+void PageDirectory::update_kernel_mappings()
+{
+    // This ensures that the kernel virtual address space is up-to-date in this page directory.
+    // This may be necessary to avoid triple faulting when entering a process's paging scope
+    // whose mappings are out-of-date.
+    memcpy(entries() + 768, MM.kernel_page_directory().entries() + 768, sizeof(PageDirectoryEntry) * 256);
+}
diff --git a/Kernel/VM/PageDirectory.h b/Kernel/VM/PageDirectory.h
index b6458c1055..3ffb438bbe 100644
--- a/Kernel/VM/PageDirectory.h
+++ b/Kernel/VM/PageDirectory.h
@@ -31,6 +31,8 @@ public:
     Process* process() { return m_process; }
     const Process* process() const { return m_process; }
 
+    void update_kernel_mappings();
+
 private:
     PageDirectory(Process&, const RangeAllocator* parent_range_allocator);
     explicit PageDirectory(PhysicalAddress);