add dynamic range configuration (#229)

Author: Freax13

Diff for: Cargo.lock

@@ -35,7 +35,7 @@ required-features = ["uefi_bin"]
 
 [dependencies]
 xmas-elf = { version = "0.8.0", optional = true }
-x86_64 = { version = "0.14.7", optional = true, default-features = false, features = ["instructions", "inline_asm"] }
+x86_64 = { version = "0.14.9", optional = true, default-features = false, features = ["instructions", "inline_asm", "step_trait"] }
 usize_conversions = { version = "0.2.0", optional = true }
 bit_field = { version = "0.10.0", optional = true }
 log = { version = "0.4.8", optional = true }

Diff for: Cargo.toml

@@ -366,6 +366,8 @@ mod binary {
         pub framebuffer_address: Option<AlignedAddress>,
         pub minimum_framebuffer_height: Option<usize>,
         pub minimum_framebuffer_width: Option<usize>,
+        pub dynamic_range_start: Option<AlignedAddress>,
+        pub dynamic_range_end: Option<AlignedAddress>,
     }
 
     /// Convert to tokens suitable for initializing the `Config` struct.
@@ -387,6 +389,8 @@ mod binary {
             let framebuffer_address = optional(self.framebuffer_address);
             let minimum_framebuffer_height = optional(self.minimum_framebuffer_height);
             let minimum_framebuffer_width = optional(self.minimum_framebuffer_width);
+            let dynamic_range_start = optional(self.dynamic_range_start);
+            let dynamic_range_end = optional(self.dynamic_range_end);
 
             tokens.extend(quote! { Config {
                 map_physical_memory: #map_physical_memory,
@@ -400,7 +404,9 @@ mod binary {
                 boot_info_address: #boot_info_address,
                 framebuffer_address: #framebuffer_address,
                 minimum_framebuffer_height: #minimum_framebuffer_height,
-                minimum_framebuffer_width: #minimum_framebuffer_width
+                minimum_framebuffer_width: #minimum_framebuffer_width,
+                dynamic_range_start: #dynamic_range_start,
+                dynamic_range_end: #dynamic_range_end,
             }});
         }
     }

Diff for: build.rs

@@ -1,4 +1,4 @@
-use core::{alloc::Layout, convert::TryInto};
+use core::{alloc::Layout, convert::TryInto, iter::Step};
 use rand::{
     distributions::{Distribution, Uniform},
     seq::IteratorRandom,
@@ -70,6 +70,28 @@ impl UsedLevel4Entries {
             }
         }
 
+        // Mark everything before the dynamic range as unusable.
+        if let Some(dynamic_range_start) = CONFIG.dynamic_range_start {
+            let dynamic_range_start = VirtAddr::new(dynamic_range_start);
+            let start_page: Page = Page::containing_address(dynamic_range_start);
+            if let Some(unusable_page) = Step::backward_checked(start_page, 1) {
+                for i in 0..=u16::from(unusable_page.p4_index()) {
+                    used.mark_p4_index_as_used(PageTableIndex::new(i));
+                }
+            }
+        }
+
+        // Mark everything after the dynamic range as unusable.
+        if let Some(dynamic_range_end) = CONFIG.dynamic_range_end {
+            let dynamic_range_end = VirtAddr::new(dynamic_range_end);
+            let end_page: Page = Page::containing_address(dynamic_range_end);
+            if let Some(unusable_page) = Step::forward_checked(end_page, 1) {
+                for i in u16::from(unusable_page.p4_index())..512 {
+                    used.mark_p4_index_as_used(PageTableIndex::new(i));
+                }
+            }
+        }
+
         used
     }
 

Diff for: src/binary/level_4_entries.rs

@@ -33,7 +33,7 @@ const PAGE_SIZE: u64 = 4096;
 ///
 /// All memory addresses are optional, even if their corresponding switch is enabled. If no
 /// address is specified, the bootloader will choose an unused entry of the level 4 page table
-/// at runtime.
+/// at runtime. The addresses can be restricted by setting the `dynamic-range` configuration key.
 #[derive(Debug)]
 pub struct Config {
     /// Whether to create a virtual mapping of the complete physical memory.
@@ -96,6 +96,14 @@ pub struct Config {
     /// `minimum_framebuffer_width` is supplied, and using the last available mode that
     /// fits them if 1 or more is set.
     pub minimum_framebuffer_width: Option<usize>,
+    /// The lowest virtual address for dynamic addresses.
+    ///
+    /// Defaults to `0`.
+    pub dynamic_range_start: Option<u64>,
+    /// The highest virtual address for dynamic addresses.
+    ///
+    /// Defaults to `0xffff_ffff_ffff_f000`.
+    pub dynamic_range_end: Option<u64>,
 }
 
 #[cfg(feature = "binary")]

Diff for: src/config.rs

@@ -67,6 +67,7 @@ for all possible configuration options.
 
 #![cfg_attr(not(feature = "builder"), no_std)]
 #![feature(maybe_uninit_slice)]
+#![feature(step_trait)]
 #![deny(unsafe_op_in_unsafe_fn)]
 #![warn(missing_docs)]
 

Diff for: src/lib.rs

@@ -8,3 +8,6 @@ edition = "2018"
 bootloader = { path = "../../.." }
 x86_64 = { version = "0.14.7", default-features = false, features = ["instructions", "inline_asm"] }
 uart_16550 = "0.2.10"
+
+[package.metadata.bootloader]
+dynamic-range-start = "0xffff_8000_0000_0000"

Diff for: tests/test_kernels/higher_half/Cargo.toml

@@ -7,11 +7,25 @@ use test_kernel_higher_half::{exit_qemu, QemuExitCode};
 
 entry_point!(kernel_main);
 
-fn kernel_main(_boot_info: &'static mut BootInfo) -> ! {
+fn kernel_main(boot_info: &'static mut BootInfo) -> ! {
     // verify that kernel is really running in the higher half of the address space
     // (set in `x86_64-higher_half.json` custom target)
     let rip = x86_64::registers::read_rip().as_u64();
     assert_eq!(rip & 0xffffffffffff0000, 0xffff800000000000);
+
+    // verify that the boot info is located in the higher half of the address space
+    assert_eq!(
+        (boot_info as *const _ as usize) & 0xffff800000000000,
+        0xffff800000000000
+    );
+
+    // verify that the stack is located in the higher half of the address space.
+    let stack_addr = &rip;
+    assert_eq!(
+        (boot_info as *const _ as usize) & 0xffff800000000000,
+        0xffff800000000000
+    );
+
     exit_qemu(QemuExitCode::Success);
 }