Fix overflow error during address calculation

fixes #275 as well as 1 additional overflow I found after looking for
similar issues

Author: Wasabi375

common/src/level_4_entries.rs

@@ -137,7 +137,7 @@ impl UsedLevel4Entries {
     /// Marks all p4 entries in the range `[address..address+size)` as used.
     fn mark_range_as_used(&mut self, address: u64, size: u64) {
         let start = VirtAddr::new(address);
-        let end_inclusive = (start + size) - 1;
+        let end_inclusive = start + (size - 1);
         let start_page = Page::<Size4KiB>::containing_address(start);
         let end_page_inclusive = Page::<Size4KiB>::containing_address(end_inclusive);
 

common/src/load_kernel.rs

@@ -504,12 +504,15 @@ where
     fn remove_copied_flags(&mut self, elf_file: &ElfFile) -> Result<(), &'static str> {
         for program_header in elf_file.program_iter() {
             if let Type::Load = program_header.get_type()? {
+                if program_header.mem_size() == 0 {
+                    continue;
+                }
                 let start = self.virtual_address_offset + program_header.virtual_addr();
-                let end = start + program_header.mem_size();
+                let end = start + (program_header.mem_size() - 1);
                 let start = VirtAddr::new(start);
                 let end = VirtAddr::new(end);
                 let start_page = Page::containing_address(start);
-                let end_page = Page::containing_address(end - 1u64);
+                let end_page = Page::containing_address(end);
                 for page in Page::<Size4KiB>::range_inclusive(start_page, end_page) {
                     // Translate the page and get the flags.
                     let res = self.page_table.translate(page.start_address());