Guard the lower 1MB of memory

.github/workflows/ci.yml

@@ -68,6 +68,9 @@ jobs:
       - uses: r7kamura/rust-problem-matchers@v1.1.0
       - name: Run api tests
         run: cargo test -p bootloader_api
+      - name: Run bootloader common tests
+        if: runner.os == 'Linux'
+        run: cargo test -p bootloader-x86_64-common
       - name: Run integration tests
         run: cargo test -- --test-threads 1
 

Cargo.toml

@@ -26,6 +26,8 @@ members = [
     "tests/test_kernels/lto",
     "tests/test_kernels/ramdisk",
     "tests/test_kernels/min_stack",
+    "tests/test_kernels/lower_memory_free",
+    "tests/test_kernels/write_usable_memory",
 ]
 exclude = ["examples/basic", "examples/test_framework"]
 
@@ -67,6 +69,8 @@ test_kernel_pie = { path = "tests/test_kernels/pie", artifact = "bin", target =
 test_kernel_ramdisk = { path = "tests/test_kernels/ramdisk", artifact = "bin", target = "x86_64-unknown-none" }
 test_kernel_config_file = { path = "tests/test_kernels/config_file", artifact = "bin", target = "x86_64-unknown-none" }
 test_kernel_min_stack = { path = "tests/test_kernels/min_stack", artifact = "bin", target = "x86_64-unknown-none" }
+test_kernel_lower_memory_free = { path = "tests/test_kernels/lower_memory_free", artifact = "bin", target = "x86_64-unknown-none" }
+test_kernel_write_usable_memory = { path = "tests/test_kernels/write_usable_memory", artifact = "bin", target = "x86_64-unknown-none" }
 
 [profile.dev]
 panic = "abort"

bios/common/src/lib.rs

@@ -5,6 +5,7 @@ pub mod racy_cell;
 #[cfg_attr(feature = "debug", derive(Debug))]
 #[repr(C)]
 pub struct BiosInfo {
+    pub stage_3: Region,
     pub stage_4: Region,
     pub kernel: Region,
     pub ramdisk: Region,

bios/stage-2/src/main.rs

@@ -145,6 +145,10 @@ fn start(disk_number: u16, partition_table_start: *const u8) -> ! {
     vesa_mode.enable().unwrap();
 
     let mut info = BiosInfo {
+        stage_3: Region {
+            start: STAGE_3_DST as u64,
+            len: stage_3_len,
+        },
         stage_4: Region {
             start: stage_4_dst as u64,
             len: stage_4_len,

bios/stage-4/src/main.rs

@@ -4,7 +4,8 @@
 use crate::memory_descriptor::MemoryRegion;
 use bootloader_api::info::{FrameBufferInfo, PixelFormat};
 use bootloader_boot_config::{BootConfig, LevelFilter};
-use bootloader_x86_64_bios_common::{BiosFramebufferInfo, BiosInfo, E820MemoryRegion};
+use bootloader_x86_64_bios_common::{BiosFramebufferInfo, BiosInfo, E820MemoryRegion, Region};
+use bootloader_x86_64_common::legacy_memory_region::UsedMemorySlice;
 use bootloader_x86_64_common::RawFrameBufferInfo;
 use bootloader_x86_64_common::{
     legacy_memory_region::LegacyFrameAllocator, load_and_switch_to_kernel, Kernel, PageTables,
@@ -55,9 +56,10 @@ pub extern "C" fn _start(info: &mut BiosInfo) -> ! {
     };
     let kernel_size = info.kernel.len;
     let next_free_frame = PhysFrame::containing_address(PhysAddr::new(info.last_used_addr)) + 1;
-    let mut frame_allocator = LegacyFrameAllocator::new_starting_at(
+    let mut frame_allocator = LegacyFrameAllocator::new_with_used_slices(
         next_free_frame,
         memory_map.iter().copied().map(MemoryRegion),
+        used_memory_slices(info),
     );
 
     // We identity-mapped all memory, so the offset between physical and virtual addresses is 0
@@ -216,6 +218,14 @@ fn init_logger(
     framebuffer_info
 }
 
+fn used_memory_slices(info: &BiosInfo) -> impl Iterator<Item = UsedMemorySlice> + Clone {
+    // skip kernel and ramdisk because they are handled individually by the
+    // uefi/bios common code
+    [info.stage_3, info.stage_4, info.config_file]
+        .into_iter()
+        .map(|region| UsedMemorySlice::new_from_len(region.start, region.len))
+}
+
 /// Creates page table abstraction types for both the bootloader and kernel page tables.
 fn create_page_tables(frame_allocator: &mut impl FrameAllocator<Size4KiB>) -> PageTables {
     // We identity-mapped all memory, so the offset between physical and virtual addresses is 0