From 2db28c7b6b4d37308f819d01e4699d810197a83c Mon Sep 17 00:00:00 2001
From: corigan01 <corigan01@gmail.com>
Date: Sat, 18 Jan 2025 15:58:26 -0600
Subject: [PATCH] Bootloader: Scrub kernel's exe memory before loading

---
 Cargo.toml                              |  6 +++---
 bootloader/stage-16bit/src/main.rs      |  2 +-
 bootloader/stage-32bit/src/multiboot.rs | 11 +++++++++--
 bootloader/stage-64bit/src/main.rs      |  1 +
 crates/mem/src/phys.rs                  | 11 +++++++++++
 5 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index fa08a53b..2e6cb991 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -97,8 +97,8 @@ overflow-checks = true
 [profile.kernel]
 inherits = "release"
 panic = "abort"
-opt-level=1
-strip = true
+opt-level=0
+strip = false
 debug = 1
 overflow-checks = true
 
@@ -106,6 +106,6 @@ overflow-checks = true
 inherits = "release"
 panic = "abort"
 opt-level=0
-strip = true
+strip = false
 debug = 1
 overflow-checks = true
diff --git a/bootloader/stage-16bit/src/main.rs b/bootloader/stage-16bit/src/main.rs
index e614f762..bdcbbe00 100644
--- a/bootloader/stage-16bit/src/main.rs
+++ b/bootloader/stage-16bit/src/main.rs
@@ -156,7 +156,7 @@ fn main(disk_id: u16) -> ! {
         stage_to_stage.video_mode = Some((closest_video_id, closest_video_info));
 
         logln!(
-            "Optimal Video Mode {:00x}): {}x{} {}bbp",
+            "Optimal Video Mode id={:#04x}: {}x{} {}bbp",
             closest_video_id.get_id(),
             closest_video_info.width,
             closest_video_info.height,
diff --git a/bootloader/stage-32bit/src/multiboot.rs b/bootloader/stage-32bit/src/multiboot.rs
index 320ce549..f1492423 100644
--- a/bootloader/stage-32bit/src/multiboot.rs
+++ b/bootloader/stage-32bit/src/multiboot.rs
@@ -501,7 +501,7 @@ pub fn get_stage_to_stage_from_multiboot_header(header: *const Multiboot1Info) -
     assert_eq!(unsafe { core::ptr::read_volatile(stack_ptr) }, 0);
 
     let header_ref = unsafe { &*header };
-    logln!("Multiboot mode! Launched from boot loader {:?}!", unsafe {
+    logln!("Multiboot mode! Launched from bootloader {:?}!", unsafe {
         core::ffi::CStr::from_ptr(header_ref.boot_loader_name as *const i8)
     });
 
@@ -512,6 +512,8 @@ pub fn get_stage_to_stage_from_multiboot_header(header: *const Multiboot1Info) -
         )
     };
 
+    // FIXME: We should make a more generic memory entry to pass around instead of
+    //        using e820 mappings.
     let mut e820_map: [bios::memory::MemoryEntry; MAX_MEMORY_MAP_ENTRIES] =
         [unsafe { core::mem::zeroed() }; MAX_MEMORY_MAP_ENTRIES];
     e820_map
@@ -523,7 +525,13 @@ pub fn get_stage_to_stage_from_multiboot_header(header: *const Multiboot1Info) -
             e820.region_type = entry.kind;
         });
 
+    // Qemu writes all of the PTRs and LENs of each of our bootloader compoenents into memory addr +1Mib
+    //
+    // You can find more details of this in the meta/main.rs file.
     let &[stage32_ptr, stage32_len, stage64_ptr, stage64_len, kernel_ptr, kernel_len, initfs_ptr, initfs_len] =
+        // FIXME: I am not sure if this is the best way of passing these arguments in, but
+        //        its also only for emulator booting so I think its fine for now. Maybe
+        //        replace in the future?
         (unsafe { core::slice::from_raw_parts(0x100000 as *const u64, 8) })
     else {
         unreachable!("Cannot match compile time length amount of elements!");
@@ -531,7 +539,6 @@ pub fn get_stage_to_stage_from_multiboot_header(header: *const Multiboot1Info) -
 
     Stage16toStage32 {
         bootloader_stack_ptr: (stack_ptr as u64, INIT_STACK.len() as u64),
-        // FIXME: We should try and link with these in the linkerscript!
         stage32_ptr: (stage32_ptr, stage32_len),
         stage64_ptr: (stage64_ptr, stage64_len),
         kernel_ptr: (kernel_ptr, kernel_len),
diff --git a/bootloader/stage-64bit/src/main.rs b/bootloader/stage-64bit/src/main.rs
index 40b9d975..95aaf2bb 100644
--- a/bootloader/stage-64bit/src/main.rs
+++ b/bootloader/stage-64bit/src/main.rs
@@ -226,6 +226,7 @@ fn build_memory_map(s2s: &Stage32toStage64, kernel_exe_len: usize) -> paging::Pa
             })
             .expect("Unable to find region for kernel pages");
         mm.add_region(kernels_pages).unwrap();
+        kernels_pages.scrub(0);
 
         let kernels_stack_pages = mm
             .find_continuous_of(PhysMemoryKind::Free, PAGE_2M, PAGE_2M, 1 * MIB as u64)
diff --git a/crates/mem/src/phys.rs b/crates/mem/src/phys.rs
index f439a00c..1c1077c2 100644
--- a/crates/mem/src/phys.rs
+++ b/crates/mem/src/phys.rs
@@ -97,6 +97,17 @@ impl PhysMemoryEntry {
     pub const fn len(&self) -> u64 {
         self.end - self.start
     }
+
+    /// Write a pattern of bytes to this area
+    ///
+    /// # Note
+    /// The pages that repr this memory entry must already be writeable and page mapped!
+    pub unsafe fn scrub(&self, byte_pattern: u8) {
+        let phys_slice = unsafe {
+            core::slice::from_raw_parts_mut(self.start as *mut u8, (self.end - self.start) as usize)
+        };
+        phys_slice.fill(byte_pattern);
+    }
 }
 
 pub struct PhysMemoryIter<'a, const N: usize> {