From 35e25757b6cffbcb2ff1eea8daf4c5f1ca421cb0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matteo=20Gm=C3=BCr?= <matteo.gmuer1@ost.ch>
Date: Wed, 16 Oct 2024 14:10:32 +0000
Subject: Adjust table accessing code to make it safer (always out of bounds
 checked)

---
 arch/x86_64/include/arch/memory/multiboot.hpp |  4 ++-
 arch/x86_64/include/arch/memory/paging.hpp    | 43 +++++++++++++++++----------
 2 files changed, 31 insertions(+), 16 deletions(-)

(limited to 'arch/x86_64/include')

diff --git a/arch/x86_64/include/arch/memory/multiboot.hpp b/arch/x86_64/include/arch/memory/multiboot.hpp
index 9a753fa..9cca8bc 100644
--- a/arch/x86_64/include/arch/memory/multiboot.hpp
+++ b/arch/x86_64/include/arch/memory/multiboot.hpp
@@ -194,7 +194,9 @@ namespace teachos::arch::memory
     auto operator==(elf_section_flags const & other) const -> bool = default;
 
   private:
-    std::bitset<64U> flags;
+    std::bitset<64U> flags;  ///< Underlying bitset used to read the flags from. Bits 21 - 28 are reserved for operating
+                             ///< system specific semantics and bits 29 - 32 are reserved for processor specific
+                             ///< semantics. Bits 33 - 64 are unused for compatability with ELF32.
   };
 
   /**
diff --git a/arch/x86_64/include/arch/memory/paging.hpp b/arch/x86_64/include/arch/memory/paging.hpp
index 4092d18..d55835e 100644
--- a/arch/x86_64/include/arch/memory/paging.hpp
+++ b/arch/x86_64/include/arch/memory/paging.hpp
@@ -110,41 +110,54 @@ namespace teachos::arch::memory
    */
   struct page_table
   {
+    /**
+     * @brief Constructor.
+     */
+    page_table();
+
     /**
      * @brief Set every entry of the page to unused
      */
     auto zero_entries() -> void;
 
     /**
-     * @brief Find and return the next table address
+     * @brief Convert the address of a page_table into a page_table
      *
-     * The next table address is only valid if the corresponding entry is present
-     * and does not create a huge page
+     * @param index Index of the entry we want to access
+     * @return An optional of the next page table or null
+     */
+    auto next_table(std::size_t index) const -> std::optional<const page_table *>;
+
+    /**
+     * @brief Index operator overload to access specific mutable entry directy
      *
-     * @param index
-     * @return An optional of the address of the next page table or null
+     * @param index Index of the entry we want to access and change
+     * @return Entry at the given table index
      */
-    auto next_table_address(std::size_t index) const -> std::optional<std::size_t>;
+    auto operator[](std::size_t index) -> entry &;
 
     /**
-     * @brief Convert the address of a page_table into a page_table
+     * @brief Index operator overload to access specific immutable entry directy
      *
-     * @param index
-     * @return An optional of the next page table or null
+     * @param index Index of the entry we want to access and only read
+     * @return Entry at the given table index
      */
-    auto next_table(std::size_t index) const -> std::optional<const page_table *>;
+    auto operator[](std::size_t index) const -> entry const &;
 
+  private:
     /**
-     * @brief Index operator overload to access specific entries directy
+     * @brief Find and return the next table address
+     *
+     * The next table address is only valid if the corresponding entry is present
+     * and does not create a huge page
      *
      * @param index
-     * @return The address of the accessed entry
+     * @return An optional of the address of the next page table or null
      */
-    entry & operator[](std::size_t index);
+    auto next_table_address(std::size_t index) const -> std::optional<std::size_t>;
 
-  private:
     entry entries[PAGE_TABLE_ENTRY_COUNT];
-    page_table const * p4 = reinterpret_cast<page_table *>(0xfffffffffffff000);
+    page_table const * p4;
   };
 }  // namespace teachos::arch::memory
 
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