Kernel: Move kmalloc heaps and super pages inside .bss segment

The kernel ignored the first 8 MiB of RAM while parsing the memory map
because the kmalloc heaps and the super physical pages lived here. Move
all that stuff inside the .bss segment so that those memory regions are
accounted for, otherwise we risk overwriting boot modules placed next
to the kernel.

Kernel/Heap/kmalloc.cpp

@@ -186,14 +186,11 @@ struct KmallocGlobalHeap {
 };
 
 static KmallocGlobalHeap* g_kmalloc_global;
+static u8 g_kmalloc_global_heap[sizeof(KmallocGlobalHeap)];
 
-// We need to make sure to not stomp on global variables or other parts
-// of the kernel image!
-extern u32 end_of_kernel_image;
-u8* const kmalloc_start = (u8*)PAGE_ROUND_UP(&end_of_kernel_image);
-u8* const kmalloc_end = kmalloc_start + (ETERNAL_RANGE_SIZE + POOL_SIZE) + sizeof(KmallocGlobalHeap);
-#define ETERNAL_BASE (kmalloc_start + sizeof(KmallocGlobalHeap))
-#define KMALLOC_BASE (ETERNAL_BASE + ETERNAL_RANGE_SIZE)
+// Treat the heap as logically separate from .bss
+__attribute__((section(".heap"))) static u8 kmalloc_eternal_heap[ETERNAL_RANGE_SIZE];
+__attribute__((section(".heap"))) static u8 kmalloc_pool_heap[POOL_SIZE];
 
 static size_t g_kmalloc_bytes_eternal = 0;
 static size_t g_kmalloc_call_count;
@@ -215,13 +212,15 @@ void kmalloc_enable_expand()
 
 void kmalloc_init()
 {
-    memset((void*)KMALLOC_BASE, 0, POOL_SIZE);
-    g_kmalloc_global = new (kmalloc_start) KmallocGlobalHeap(KMALLOC_BASE, POOL_SIZE); // Place heap at kmalloc_start
+    // Zero out heap since it's placed after end_of_kernel_bss.
+    memset(kmalloc_eternal_heap, 0, sizeof(kmalloc_eternal_heap));
+    memset(kmalloc_pool_heap, 0, sizeof(kmalloc_pool_heap));
+    g_kmalloc_global = new (g_kmalloc_global_heap) KmallocGlobalHeap(kmalloc_pool_heap, sizeof(kmalloc_pool_heap));
 
     s_lock.initialize();
 
-    s_next_eternal_ptr = (u8*)ETERNAL_BASE;
-    s_end_of_eternal_range = s_next_eternal_ptr + ETERNAL_RANGE_SIZE;
+    s_next_eternal_ptr = kmalloc_eternal_heap;
+    s_end_of_eternal_range = s_next_eternal_ptr + sizeof(kmalloc_pool_heap);
 }
 
 void* kmalloc_eternal(size_t size)

Kernel/Heap/kmalloc.h

@@ -82,6 +82,3 @@ inline void kfree_aligned(void* ptr)
 }
 
 void kmalloc_enable_expand();
-
-extern u8* const kmalloc_start;
-extern u8* const kmalloc_end;

Kernel/VM/MemoryManager.cpp

@@ -49,6 +49,12 @@ extern FlatPtr start_of_kernel_text;
 extern FlatPtr start_of_kernel_data;
 extern FlatPtr end_of_kernel_bss;
 
+extern multiboot_module_entry_t multiboot_copy_boot_modules_array[16];
+extern size_t multiboot_copy_boot_modules_count;
+
+// Treat the super pages as logically separate from .bss
+__attribute__((section(".super_pages"))) static u8 super_pages[1 * MiB];
+
 namespace Kernel {
 
 // NOTE: We can NOT use AK::Singleton for this class, because
@@ -103,14 +109,9 @@ void MemoryManager::protect_kernel_image()
         auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
         pte.set_writable(false);
     }
-
     if (Processor::current().has_feature(CPUFeature::NX)) {
-        // Disable execution of the kernel data and bss segments, as well as the kernel heap.
-        for (size_t i = (FlatPtr)&start_of_kernel_data; i < (FlatPtr)&end_of_kernel_bss; i += PAGE_SIZE) {
-            auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
-            pte.set_execute_disabled(true);
-        }
-        for (size_t i = FlatPtr(kmalloc_start); i < FlatPtr(kmalloc_end); i += PAGE_SIZE) {
+        // Disable execution of the kernel data, bss and heap segments.
+        for (size_t i = (FlatPtr)&start_of_kernel_data; i < (FlatPtr)&end_of_kernel_image; i += PAGE_SIZE) {
             auto& pte = *ensure_pte(kernel_page_directory(), VirtualAddress(i));
             pte.set_execute_disabled(true);
         }
@@ -120,14 +121,12 @@ void MemoryManager::protect_kernel_image()
 void MemoryManager::parse_memory_map()
 {
     RefPtr<PhysicalRegion> region;
-    bool region_is_super = false;
 
     // We need to make sure we exclude the kmalloc range as well as the kernel image.
     // The kmalloc range directly follows the kernel image
     const PhysicalAddress used_range_start(virtual_to_low_physical(FlatPtr(&start_of_kernel_image)));
-    const PhysicalAddress used_range_end(PAGE_ROUND_UP(virtual_to_low_physical(FlatPtr(kmalloc_end))));
-    klog() << "MM: kernel range: " << used_range_start << " - " << PhysicalAddress(PAGE_ROUND_UP(virtual_to_low_physical(FlatPtr(&end_of_kernel_image))));
-    klog() << "MM: kmalloc range: " << PhysicalAddress(virtual_to_low_physical(FlatPtr(kmalloc_start))) << " - " << used_range_end;
+    const PhysicalAddress used_range_end(virtual_to_low_physical(FlatPtr(&end_of_kernel_image)));
+    klog() << "MM: kernel range: " << used_range_start << " - " << used_range_end;
 
     auto* mmap = (multiboot_memory_map_t*)(low_physical_to_virtual(multiboot_info_ptr->mmap_addr));
     for (; (unsigned long)mmap < (low_physical_to_virtual(multiboot_info_ptr->mmap_addr)) + (multiboot_info_ptr->mmap_length); mmap = (multiboot_memory_map_t*)((unsigned long)mmap + mmap->size + sizeof(mmap->size))) {
@@ -161,31 +160,32 @@ void MemoryManager::parse_memory_map()
         for (size_t page_base = mmap->addr; page_base <= (mmap->addr + mmap->len); page_base += PAGE_SIZE) {
             auto addr = PhysicalAddress(page_base);
 
-            if (addr.get() < used_range_end.get() && addr.get() >= used_range_start.get())
+            // Skip used memory ranges.
+            bool should_skip = false;
+            for (auto used_range : m_used_memory_ranges) {
+                if (addr.get() >= used_range.start.get() && addr.get() <= used_range.end.get()) {
+                    should_skip = true;
+                    break;
+                }
+            }
+            if (should_skip)
                 continue;
 
-            if (page_base < 7 * MiB) {
-                // nothing
-            } else if (page_base >= 7 * MiB && page_base < 8 * MiB) {
-                if (region.is_null() || !region_is_super || region->upper().offset(PAGE_SIZE) != addr) {
-                    m_super_physical_regions.append(PhysicalRegion::create(addr, addr));
-                    region = m_super_physical_regions.last();
-                    region_is_super = true;
-                } else {
-                    region->expand(region->lower(), addr);
-                }
+            // Assign page to user physical region.
+            if (region.is_null() || region->upper().offset(PAGE_SIZE) != addr) {
+                m_user_physical_regions.append(PhysicalRegion::create(addr, addr));
+                region = m_user_physical_regions.last();
             } else {
-                if (region.is_null() || region_is_super || region->upper().offset(PAGE_SIZE) != addr) {
-                    m_user_physical_regions.append(PhysicalRegion::create(addr, addr));
-                    region = m_user_physical_regions.last();
-                    region_is_super = false;
-                } else {
-                    region->expand(region->lower(), addr);
-                }
+                region->expand(region->lower(), addr);
             }
         }
     }
 
+    // Append statically-allocated super physical region.
+    m_super_physical_regions.append(PhysicalRegion::create(
+        PhysicalAddress(virtual_to_low_physical(FlatPtr(super_pages))),
+        PhysicalAddress(virtual_to_low_physical(FlatPtr(super_pages + sizeof(super_pages))))));
+
     for (auto& region : m_super_physical_regions) {
         m_super_physical_pages += region.finalize_capacity();
         klog() << "Super physical region: " << region.lower() << " - " << region.upper();

Kernel/linker.ld

@@ -44,13 +44,18 @@ SECTIONS
         end_of_kernel_data = .;
     }
 
-    .bss ALIGN(4K) : AT (ADDR(.bss) - 0xc0000000)
+    .bss ALIGN(4K) (NOLOAD) : AT (ADDR(.bss) - 0xc0000000)
     {
         start_of_kernel_bss = .;
         *(page_tables)
         *(COMMON)
         *(.bss)
         end_of_kernel_bss = .;
+
+        . = ALIGN(4K);
+        *(.heap)
+        . = ALIGN(4K);
+        *(.super_pages)
     }
 
     end_of_kernel_image = .;