Merge pull request #494 from Wasabi375/fixed_entry

Specify kernel-code virt addr in BootloaderConfig

Cargo.toml

@@ -60,6 +60,7 @@ test_kernel_config_file = { path = "tests/test_kernels/config_file", artifact =
 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" }
+test_kernel_fixed_kernel_address = { path = "tests/test_kernels/fixed_kernel_address", artifact = "bin", target = "x86_64-unknown-none" }
 
 [profile.dev]
 panic = "abort"

Changelog.md

@@ -1,5 +1,11 @@
 # Unreleased
 
+## Features
+
+* add `kernel_base` mapping to the BootloaderConfig to specify the virtual address
+    at which position-independent kernels are loaded.
+
+
 # 0.11.10 – 2025-02-10
 
 * [Remove "UEFI boot" log message](https://github.com/rust-osdev/bootloader/pull/476)

api/build.rs

@@ -15,14 +15,15 @@ fn main() {
         (31, 9),
         (40, 9),
         (49, 9),
-        (58, 10),
-        (68, 10),
-        (78, 1),
-        (79, 9),
+        (58, 9),
+        (67, 10),
+        (77, 10),
+        (87, 1),
         (88, 9),
         (97, 9),
         (106, 9),
         (115, 9),
+        (124, 9),
     ];
 
     let mut code = String::new();

api/src/config.rs

@@ -43,7 +43,7 @@ impl BootloaderConfig {
         0x3D,
     ];
     #[doc(hidden)]
-    pub const SERIALIZED_LEN: usize = 124;
+    pub const SERIALIZED_LEN: usize = 133;
 
     /// Creates a new default configuration with the following values:
     ///
@@ -77,6 +77,7 @@ impl BootloaderConfig {
         } = version;
         let Mappings {
             kernel_stack,
+            kernel_base,
             boot_info,
             framebuffer,
             physical_memory,
@@ -97,53 +98,56 @@ impl BootloaderConfig {
             concat_4_3(one, two)
         };
         let buf = concat_16_7(Self::UUID, version);
+
         let buf = concat_23_8(buf, kernel_stack_size.to_le_bytes());
 
         let buf = concat_31_9(buf, kernel_stack.serialize());
-        let buf = concat_40_9(buf, boot_info.serialize());
-        let buf = concat_49_9(buf, framebuffer.serialize());
+        let buf = concat_40_9(buf, kernel_base.serialize());
+
+        let buf = concat_49_9(buf, boot_info.serialize());
+        let buf = concat_58_9(buf, framebuffer.serialize());
 
-        let buf = concat_58_10(
+        let buf = concat_67_10(
             buf,
             match physical_memory {
                 Option::None => [0; 10],
                 Option::Some(m) => concat_1_9([1], m.serialize()),
             },
         );
-        let buf = concat_68_10(
+        let buf = concat_77_10(
             buf,
             match page_table_recursive {
                 Option::None => [0; 10],
                 Option::Some(m) => concat_1_9([1], m.serialize()),
             },
         );
-        let buf = concat_78_1(buf, [(*aslr) as u8]);
-        let buf = concat_79_9(
+        let buf = concat_87_1(buf, [(*aslr) as u8]);
+        let buf = concat_88_9(
             buf,
             match dynamic_range_start {
                 Option::None => [0; 9],
                 Option::Some(addr) => concat_1_8([1], addr.to_le_bytes()),
             },
         );
-        let buf = concat_88_9(
+        let buf = concat_97_9(
             buf,
             match dynamic_range_end {
                 Option::None => [0; 9],
                 Option::Some(addr) => concat_1_8([1], addr.to_le_bytes()),
             },
         );
 
-        let buf = concat_97_9(buf, ramdisk_memory.serialize());
+        let buf = concat_106_9(buf, ramdisk_memory.serialize());
 
-        let buf = concat_106_9(
+        let buf = concat_115_9(
             buf,
             match minimum_framebuffer_height {
                 Option::None => [0; 9],
                 Option::Some(addr) => concat_1_8([1], addr.to_le_bytes()),
             },
         );
 
-        concat_115_9(
+        concat_124_9(
             buf,
             match minimum_framebuffer_width {
                 Option::None => [0; 9],
@@ -196,6 +200,7 @@ impl BootloaderConfig {
 
         let (mappings, s) = {
             let (&kernel_stack, s) = split_array_ref(s);
+            let (&kernel_base, s) = split_array_ref(s);
             let (&boot_info, s) = split_array_ref(s);
             let (&framebuffer, s) = split_array_ref(s);
             let (&physical_memory_some, s) = split_array_ref(s);
@@ -211,6 +216,7 @@ impl BootloaderConfig {
 
             let mappings = Mappings {
                 kernel_stack: Mapping::deserialize(&kernel_stack)?,
+                kernel_base: Mapping::deserialize(&kernel_base)?,
                 boot_info: Mapping::deserialize(&boot_info)?,
                 framebuffer: Mapping::deserialize(&framebuffer)?,
                 physical_memory: match physical_memory_some {
@@ -371,6 +377,11 @@ pub struct Mappings {
     /// `FixedAddress(0xf_0000_0000)` will result in a guard page at address
     /// `0xf_0000_0000` and the kernel stack starting at address `0xf_0000_1000`.
     pub kernel_stack: Mapping,
+    /// Configures the base address of the kernel.
+    ///
+    /// If a fixed address is set, it must be paged aligned and the kernel must be
+    /// a position-independent exectuable.
+    pub kernel_base: Mapping,
     /// Specifies where the [`crate::BootInfo`] struct should be placed in virtual memory.
     pub boot_info: Mapping,
     /// Specifies the mapping of the frame buffer memory region.
@@ -413,6 +424,7 @@ impl Mappings {
     pub const fn new_default() -> Self {
         Self {
             kernel_stack: Mapping::new_default(),
+            kernel_base: Mapping::new_default(),
             boot_info: Mapping::new_default(),
             framebuffer: Mapping::new_default(),
             physical_memory: Option::None,
@@ -430,6 +442,7 @@ impl Mappings {
         let recursive = rand::random();
         Self {
             kernel_stack: Mapping::random(),
+            kernel_base: Mapping::random(),
             boot_info: Mapping::random(),
             framebuffer: Mapping::random(),
             physical_memory: if phys {

common/src/legacy_memory_region.rs

@@ -1,9 +1,5 @@
 use bootloader_api::info::{MemoryRegion, MemoryRegionKind};
-use core::{
-    cmp,
-    iter::{empty, Empty},
-    mem::MaybeUninit,
-};
+use core::{cmp, mem::MaybeUninit};
 use x86_64::{
     align_down, align_up,
     structures::paging::{FrameAllocator, PhysFrame, Size4KiB},

common/src/level_4_entries.rs

@@ -1,4 +1,8 @@
-use crate::{entropy, load_kernel::VirtualAddressOffset, BootInfo, RawFrameBufferInfo};
+use crate::{
+    entropy,
+    load_kernel::{calc_elf_memory_requirements, ElfMemoryRequirements, VirtualAddressOffset},
+    BootInfo, RawFrameBufferInfo,
+};
 use bootloader_api::{config, info::MemoryRegion, BootloaderConfig};
 use core::{alloc::Layout, iter::Step};
 use rand::{
@@ -11,7 +15,7 @@ use x86_64::{
     structures::paging::{Page, PageTableIndex, Size4KiB},
     PhysAddr, VirtAddr,
 };
-use xmas_elf::program::ProgramHeader;
+use xmas_elf::{header, program::ProgramHeader, ElfFile};
 
 /// Keeps track of used entries in a level 4 page table.
 ///
@@ -33,7 +37,8 @@ impl UsedLevel4Entries {
         regions_len: usize,
         framebuffer: Option<&RawFrameBufferInfo>,
         config: &BootloaderConfig,
-    ) -> Self {
+        kernel_elf: &ElfFile<'_>,
+    ) -> Result<Self, &'static str> {
         let mut used = UsedLevel4Entries {
             entry_state: [false; 512],
             rng: config.mappings.aslr.then(entropy::build_rng),
@@ -73,6 +78,23 @@ impl UsedLevel4Entries {
             used.mark_range_as_used(kernel_stack_address, config.kernel_stack_size);
         }
 
+        if let config::Mapping::FixedAddress(kernel_base) = config.mappings.kernel_base {
+            let ElfMemoryRequirements { size, align, .. } =
+                calc_elf_memory_requirements(kernel_elf);
+
+            if !VirtAddr::new(kernel_base).is_aligned(align) {
+                return Err("kernel_code mapping alignment does not match elf file");
+            }
+
+            used.mark_range_as_used(kernel_base, size);
+        }
+        if kernel_elf.header.pt2.type_().as_type() == header::Type::Executable {
+            let ElfMemoryRequirements { size, min_addr, .. } =
+                calc_elf_memory_requirements(kernel_elf);
+
+            used.mark_range_as_used(min_addr, size);
+        }
+
         if let config::Mapping::FixedAddress(boot_info_address) = config.mappings.boot_info {
             let boot_info_layout = Layout::new::<BootInfo>();
             let regions = regions_len + 1; // one region might be split into used/unused
@@ -110,7 +132,7 @@ impl UsedLevel4Entries {
             }
         }
 
-        used
+        Ok(used)
     }
 
     /// Marks all p4 entries in the range `[address..address+size)` as used.

common/src/lib.rs

@@ -187,7 +187,9 @@ where
         frame_allocator.len(),
         framebuffer,
         config,
-    );
+        &kernel.elf,
+    )
+    .expect("Failed to mark level 4 entries as used");
 
     // Enable support for the no-execute bit in page tables.
     enable_nxe_bit();

common/src/load_kernel.rs

@@ -1,5 +1,5 @@
 use crate::{level_4_entries::UsedLevel4Entries, PAGE_SIZE};
-use bootloader_api::info::TlsTemplate;
+use bootloader_api::{config::Mapping, info::TlsTemplate};
 use core::{cmp, iter::Step, mem::size_of, ops::Add};
 
 use x86_64::{
@@ -59,27 +59,30 @@ where
         let virtual_address_offset = match elf_file.header.pt2.type_().as_type() {
             header::Type::None => unimplemented!(),
             header::Type::Relocatable => unimplemented!(),
-            header::Type::Executable => VirtualAddressOffset::zero(),
+            header::Type::Executable => match kernel.config.mappings.kernel_base {
+                Mapping::Dynamic => VirtualAddressOffset::zero(),
+                _ => {
+                    return Err(concat!(
+                        "Invalid kernel_code mapping. ",
+                        "Executable can only be mapped at virtual_address_offset 0."
+                    ))
+                }
+            },
             header::Type::SharedObject => {
-                // Find the highest virtual memory address and the biggest alignment.
-                let load_program_headers = elf_file
-                    .program_iter()
-                    .filter(|h| matches!(h.get_type(), Ok(Type::Load)));
-                let max_addr = load_program_headers
-                    .clone()
-                    .map(|h| h.virtual_addr() + h.mem_size())
-                    .max()
-                    .unwrap_or(0);
-                let min_addr = load_program_headers
-                    .clone()
-                    .map(|h| h.virtual_addr())
-                    .min()
-                    .unwrap_or(0);
-                let size = max_addr - min_addr;
-                let align = load_program_headers.map(|h| h.align()).max().unwrap_or(1);
-
-                let offset = used_entries.get_free_address(size, align).as_u64();
-                VirtualAddressOffset::new(i128::from(offset) - i128::from(min_addr))
+                let ElfMemoryRequirements {
+                    size,
+                    align,
+                    min_addr,
+                } = calc_elf_memory_requirements(&elf_file);
+                match kernel.config.mappings.kernel_base {
+                    Mapping::Dynamic => {
+                        let offset = used_entries.get_free_address(size, align).as_u64();
+                        VirtualAddressOffset::new(i128::from(offset) - i128::from(min_addr))
+                    }
+                    Mapping::FixedAddress(address) => {
+                        VirtualAddressOffset::new(i128::from(address))
+                    }
+                }
             }
             header::Type::Core => unimplemented!(),
             header::Type::ProcessorSpecific(_) => unimplemented!(),
@@ -750,6 +753,41 @@ pub fn load_kernel(
     ))
 }
 
+/// Basic information about the memory segments of an elf file.
+pub struct ElfMemoryRequirements {
+    /// total size needed for all segments
+    pub size: u64,
+    /// memory alignment for the elf file
+    pub align: u64,
+    /// the smallest virtual address used by the elf file
+    pub min_addr: u64,
+}
+
+/// Calculates basic requirements needed to allocate memory for an elf file.
+pub fn calc_elf_memory_requirements(elf_file: &ElfFile) -> ElfMemoryRequirements {
+    // Find the highest virtual memory address and the biggest alignment.
+    let load_program_headers = elf_file
+        .program_iter()
+        .filter(|h| matches!(h.get_type(), Ok(Type::Load)));
+    let max_addr = load_program_headers
+        .clone()
+        .map(|h| h.virtual_addr() + h.mem_size())
+        .max()
+        .unwrap_or(0);
+    let min_addr = load_program_headers
+        .clone()
+        .map(|h| h.virtual_addr())
+        .min()
+        .unwrap_or(0);
+    let size = max_addr - min_addr;
+    let align = load_program_headers.map(|h| h.align()).max().unwrap_or(1);
+    ElfMemoryRequirements {
+        size,
+        align,
+        min_addr,
+    }
+}
+
 /// A helper type used to offset virtual addresses for position independent
 /// executables.
 #[derive(Clone, Copy)]