Kernel: Always observe the return value of Region::map and remap

We have seen cases where the map fails, but we return the region
to the caller, causing them to page fault later on when they touch
the region.

The fix is to always observe the return code of map/remap.

Kernel/Memory/AddressSpace.cpp

@@ -80,7 +80,10 @@ KResult AddressSpace::unmap_mmap_range(VirtualAddress addr, size_t size)
 
         // And finally we map the new region(s) using our page directory (they were just allocated and don't have one).
         for (auto* new_region : new_regions) {
-            new_region->map(page_directory());
+            // TODO: Ideally we should do this in a way that can be rolled back on failure, as failing here
+            // leaves the caller in an undefined state.
+            if (!new_region->map(page_directory()))
+                return ENOMEM;
         }
 
         PerformanceManager::add_unmap_perf_event(Process::current(), range_to_unmap);
@@ -130,7 +133,10 @@ KResult AddressSpace::unmap_mmap_range(VirtualAddress addr, size_t size)
 
     // And finally map the new region(s) into our page directory.
     for (auto* new_region : new_regions) {
-        new_region->map(page_directory());
+        // TODO: Ideally we should do this in a way that can be rolled back on failure, as failing here
+        // leaves the caller in an undefined state.
+        if (!new_region->map(page_directory()))
+            return ENOMEM;
     }
 
     PerformanceManager::add_unmap_perf_event(Process::current(), range_to_unmap);

Kernel/Memory/MemoryManager.cpp

@@ -748,7 +748,8 @@ OwnPtr<Region> MemoryManager::allocate_kernel_region_with_vmobject(VirtualRange
         return {};
 
     auto region = maybe_region.release_value();
-    region->map(kernel_page_directory());
+    if (!region->map(kernel_page_directory()))
+        return {};
     return region;
 }
 

Kernel/Memory/Region.cpp

@@ -285,7 +285,8 @@ bool Region::map(PageDirectory& page_directory, ShouldFlushTLB should_flush_tlb)
 void Region::remap()
 {
     VERIFY(m_page_directory);
-    map(*m_page_directory);
+    auto result = map(*m_page_directory);
+    VERIFY(result);
 }
 
 PageFaultResponse Region::handle_fault(PageFault const& fault)
@@ -310,7 +311,8 @@ PageFaultResponse Region::handle_fault(PageFault const& fault)
             auto page_index_in_vmobject = translate_to_vmobject_page(page_index_in_region);
             VERIFY(m_vmobject->is_anonymous());
             page_slot = static_cast<AnonymousVMObject&>(*m_vmobject).allocate_committed_page({});
-            remap_vmobject_page(page_index_in_vmobject);
+            if (!remap_vmobject_page(page_index_in_vmobject))
+                return PageFaultResponse::OutOfMemory;
             return PageFaultResponse::Continue;
         }
         dbgln("BUG! Unexpected NP fault at {}", fault.vaddr());
@@ -458,7 +460,9 @@ PageFaultResponse Region::handle_inode_fault(size_t page_index_in_region)
         MM.unquickmap_page();
     }
 
-    remap_vmobject_page(page_index_in_vmobject);
+    if (!remap_vmobject_page(page_index_in_vmobject))
+        return PageFaultResponse::OutOfMemory;
+
     return PageFaultResponse::Continue;
 }
 

Kernel/Syscalls/fork.cpp

@@ -109,7 +109,8 @@ KResultOr<FlatPtr> Process::sys$fork(RegisterState& regs)
                 // TODO: tear down new process?
                 return ENOMEM;
             }
-            child_region->map(child->address_space().page_directory(), Memory::ShouldFlushTLB::No);
+            if (!child_region->map(child->address_space().page_directory(), Memory::ShouldFlushTLB::No))
+                return ENOMEM;
 
             if (region == m_master_tls_region.unsafe_ptr())
                 child->m_master_tls_region = child_region;

Kernel/Syscalls/mmap.cpp

@@ -347,7 +347,7 @@ KResultOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int
         }
 
         // Remove the old region from our regions tree, since were going to add another region
-        // with the exact same start address, but dont deallocate it yet
+        // with the exact same start address, but do not deallocate it yet
         auto region = address_space().take_region(*old_region);
 
         // Unmap the old region here, specifying that we *don't* want the VM deallocated.
@@ -371,9 +371,11 @@ KResultOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int
 
         // Map the new regions using our page directory (they were just allocated and don't have one).
         for (auto* adjacent_region : adjacent_regions) {
-            adjacent_region->map(address_space().page_directory());
+            if (!adjacent_region->map(address_space().page_directory()))
+                return ENOMEM;
         }
-        new_region.map(address_space().page_directory());
+        if (!new_region.map(address_space().page_directory()))
+            return ENOMEM;
         return 0;
     }
 
@@ -438,9 +440,11 @@ KResultOr<FlatPtr> Process::sys$mprotect(Userspace<void*> addr, size_t size, int
 
             // Map the new region using our page directory (they were just allocated and don't have one) if any.
             if (adjacent_regions.size())
-                adjacent_regions[0]->map(address_space().page_directory());
+                if (!adjacent_regions[0]->map(address_space().page_directory()))
+                    return ENOMEM;
 
-            new_region.map(address_space().page_directory());
+            if (!new_region.map(address_space().page_directory()))
+                return ENOMEM;
         }
 
         return 0;