Avoid overwriting bootloader data

src/kernel/boot/multiboot.c

@@ -1,6 +1,7 @@
 #include <stdint.h>
 #include <multiboot.h>
 #include <memory.h>
+#include <debug.h>
 
 // https://www.gnu.org/software/grub/manual/multiboot2/multiboot.html
 
@@ -39,7 +40,7 @@ struct fbinfo {
     uint8_t data[];
 }__attribute__((packed));
 
-int parse_multiboot2(struct taglist *tags)
+static int parse_multiboot2(struct taglist *tags)
 {
     struct mmap *mmap;
 
@@ -96,3 +97,17 @@ int multiboot_get_memory_area(size_t index, uintptr_t *start, uintptr_t *end, ui
     *type = entry->type;
     return 0;
 }
+
+int multiboot_page_used(uintptr_t page)
+{
+    #define within_page(st, l) (((uintptr_t)st + l) > page && (uintptr_t)st < (page + PAGE_SIZE))
+    if(
+        within_page(kernel_boot_data.bootloader, strlen(kernel_boot_data.bootloader)) ||
+        within_page(kernel_boot_data.commandline, strlen(kernel_boot_data.commandline)) ||
+        within_page(kernel_boot_data.mmap, kernel_boot_data.mmap_size) ||
+    0) {
+        debug("Page %x used\n", page);
+        return 1;
+    }
+    return 0;
+}

src/kernel/include/multiboot.h

@@ -30,4 +30,5 @@ extern struct kernel_boot_data_st kernel_boot_data;
 // boot/multiboot.c
 int multiboot_init(uint64_t magic, void *mboot_info);
 int multiboot_get_memory_area(size_t index, uintptr_t *start, uintptr_t *end, uint32_t *type);
+int multiboot_page_used(uintptr_t page);
 #endif

src/kernel/memory/memory.c

@@ -19,9 +19,6 @@ void memory_init()
 
         for(uint64_t p = start; p < end; p += PAGE_SIZE)
         {
-            if(p >= V2P(&kernel_start) && p < V2P(&kernel_end))
-                continue;
-
             uint64_t vaddr = (uint64_t)P2V(p);
             uint64_t page = vmm_get_page(kernel_P4, vaddr);
             if(page == (uint64_t)-1 || !(page & PAGE_PRESENT))
@@ -30,7 +27,13 @@ void memory_init()
                 vmm_set_page(kernel_P4, vaddr, p, flags);
             }
 
-            if(type == MMAP_FREE)
+            if(type != MMAP_FREE)
+                continue;
+            if(p >= V2P(&kernel_start) && p < V2P(&kernel_end))
+                continue;
+            if(multiboot_page_used((uintptr_t)P2V(p)))
+                continue;
+
             pmm_free(p);
         }
     }