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core: Reserve kernel physical pages + provide our own stack

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This solves a very weird bug that occurred when we allocated a page that was already used for the stack.
This commit is contained in:
Gabriel 2025-02-24 19:16:35 +01:00
parent d3231f1362
commit c5876768c5
4 changed files with 97 additions and 50 deletions
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16
core/src/arch/x86_64/platform.zig
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@ -1,3 +1,4 @@
const std = @import("std");
const gdt = @import("gdt.zig");
const idt = @import("idt.zig");
const pic = @import("pic.zig");
@ -18,6 +19,21 @@ fn enableNX() void {
);
}
var stack: [PAGE_SIZE * 8]u8 = std.mem.zeroes([PAGE_SIZE * 8]u8);
const top: usize = (PAGE_SIZE * 8) - 16;
pub inline fn _start() noreturn {
asm volatile (
\\ mov %[stack], %rsp
\\ addq %[top], %rsp
\\ call main
:
: [stack] "i" (&stack),
[top] "i" (top),
);
unreachable;
}
// Initialize platform-specific components.
pub fn platformInit() void {
gdt.setupGDT();

14
core/src/arch/x86_64/vmm.zig
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@ -3,6 +3,7 @@ const easyboot = @cImport(@cInclude("easyboot.h"));
const mmap = @import("../../mmap.zig");
const pmm = @import("../../pmm.zig");
const platform = @import("platform.zig");
const debug = @import("../debug.zig");
const USER_ADDRESS_RANGE_END = 0x0000_7fff_ffff_ffff;
pub const PHYSICAL_MAPPING_BASE = 0xffff_8000_0000_0000;
@ -151,6 +152,11 @@ pub fn getEntry(space: AddressSpace, base: usize, virt_address: u64) ?*PageTable
return pt_entry;
}
pub fn getAddress(space: AddressSpace, base: usize, virt_address: u64) ?usize {
const entry = getEntry(space, base, virt_address) orelse return null;
return entry.getAddress();
}
pub fn copyToUser(space: AddressSpace, base: usize, user: usize, kernel: [*]const u8, size: usize) !void {
const remainder: usize = @rem(user, platform.PAGE_SIZE);
const user_page = user - remainder;
@ -277,22 +283,20 @@ fn setUpKernelPageDirectory(allocator: *pmm.FrameAllocator, tag: *easyboot.multi
return table;
}
pub fn setUpInitialUserPageDirectory(allocator: *pmm.FrameAllocator, tag: *easyboot.multiboot_tag_mmap_t, user_table: *PageTable) !usize {
pub fn setUpInitialUserPageDirectory(allocator: *pmm.FrameAllocator, tag: *easyboot.multiboot_tag_mmap_t, space: AddressSpace) !usize {
const kernel_space = AddressSpace.create(readPageTable(), PHYSICAL_MAPPING_BASE);
const kernel_table = kernel_space.table;
const physical_address_space_size = mmap.getAddressSpaceSize(tag) orelse return error.InvalidMemoryMap;
user_table.* = std.mem.zeroes(PageTable);
space.table.* = std.mem.zeroes(PageTable);
const directory_upper_half: *[256]PageTableEntry = kernel_table.entries[256..];
const user_directory_upper_half: *[256]PageTableEntry = user_table.entries[256..];
const user_directory_upper_half: *[256]PageTableEntry = space.table.entries[256..];
@memcpy(user_directory_upper_half, directory_upper_half);
const user_physical_address_base = (USER_ADDRESS_RANGE_END + 1) - physical_address_space_size;
const space = AddressSpace.create(.{ .address = @intFromPtr(user_table) }, 0);
try mapPhysicalMemory(allocator, tag, space, PHYSICAL_MAPPING_BASE, user_physical_address_base, @intFromEnum(Flags.ReadWrite) | @intFromEnum(Flags.NoExecute) | @intFromEnum(Flags.User));
return user_physical_address_base;

50
core/src/main.zig
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@ -13,51 +13,11 @@ const elf = @import("elf.zig");
const MultibootInfo = [*c]u8;
fn adjustAddressToPageBoundary(address: *usize, size: *usize) void {
const diff = address.* % platform.PAGE_SIZE;
address.* -= diff;
size.* += diff;
export fn _start(_: u32, _: MultibootInfo) callconv(.C) noreturn {
platform._start();
}
fn reserveMultibootMemory(allocator: *pmm.FrameAllocator, info: MultibootInfo) !void {
const info_tag: *easyboot.multiboot_info_t = @alignCast(@ptrCast(info));
var address: usize = @intFromPtr(info);
var size: usize = info_tag.total_size;
adjustAddressToPageBoundary(&address, &size);
debug.print("Locking multiboot memory at {x}, {d} bytes\n", .{ address, size });
try pmm.lockFrames(allocator, address, try std.math.divCeil(usize, size, platform.PAGE_SIZE));
const Context = struct {
allocator: *pmm.FrameAllocator,
};
var ctx = Context{ .allocator = allocator };
multiboot.findMultibootTags(easyboot.multiboot_tag_module_t, @ptrCast(info), struct {
fn reserveMemory(mod: *easyboot.multiboot_tag_module_t, context: *const Context) !void {
var mod_address: usize = mod.mod_start;
var mod_size: usize = mod.mod_end - mod.mod_start;
adjustAddressToPageBoundary(&mod_address, &mod_size);
debug.print("Locking memory for module {s} at address {x}, {d} bytes\n", .{ mod.string(), mod_address, mod_size });
try pmm.lockFrames(context.allocator, mod_address, try std.math.divCeil(usize, mod_size, platform.PAGE_SIZE));
}
fn handler(mod: *easyboot.multiboot_tag_module_t, context: *const anyopaque) void {
reserveMemory(mod, @alignCast(@ptrCast(context))) catch |err| {
debug.print("Error while reserving multiboot memory {s}: {}\n", .{ mod.string(), err });
while (true) {}
};
}
}.handler, &ctx);
}
export fn _start(magic: u32, info: MultibootInfo) callconv(.C) noreturn {
export fn main(magic: u32, info: MultibootInfo) callconv(.C) noreturn {
interrupts.disableInterrupts();
if (magic != easyboot.MULTIBOOT2_BOOTLOADER_MAGIC) {
@ -80,7 +40,7 @@ export fn _start(magic: u32, info: MultibootInfo) callconv(.C) noreturn {
while (true) {}
};
reserveMultibootMemory(&allocator, info) catch |err| {
pmm.reserveMultibootMemory(&allocator, info) catch |err| {
debug.print("Error while reserving multiboot memory: {}\n", .{err});
while (true) {}
};
@ -108,7 +68,7 @@ export fn _start(magic: u32, info: MultibootInfo) callconv(.C) noreturn {
const frame = try pmm.allocFrame(context.allocator);
const space = vmm.AddressSpace.create(frame, vmm.PHYSICAL_MAPPING_BASE);
const base = try vmm.setUpInitialUserPageDirectory(context.allocator, context.mmap, space.table);
const base = try vmm.setUpInitialUserPageDirectory(context.allocator, context.mmap, space);
const module = try thread.createThreadControlBlock(context.allocator);

67
core/src/pmm.zig
View File

@ -5,6 +5,8 @@ const vmm = @import("arch/vmm.zig");
const mmap = @import("mmap.zig");
const bmap = @import("lib/bitmap.zig");
const locking = @import("lib/spinlock.zig");
const debug = @import("arch/debug.zig");
const multiboot = @import("multiboot.zig");
const FrameAllocatorError = error{
InvalidMemoryMap,
@ -104,9 +106,74 @@ pub fn initializeFrameAllocator(tag: *easyboot.multiboot_tag_mmap_t) !FrameAlloc
// Avoid causing trouble.
try lockFrame(&allocator, 0);
try reserveKernelMemory(&allocator);
return allocator;
}
fn adjustAddressToPageBoundary(address: *usize, size: *usize) void {
const diff = address.* % platform.PAGE_SIZE;
address.* -= diff;
size.* += diff;
}
extern const kernel_start: [*]u8;
extern const kernel_end: [*]u8;
fn reserveKernelMemory(allocator: *FrameAllocator) !void {
debug.print("Kernel begins at {*} and ends at {*}\n", .{ &kernel_start, &kernel_end });
const start: usize = @intFromPtr(&kernel_start);
const end: usize = @intFromPtr(&kernel_end);
const pages = try std.math.divCeil(usize, end - start, platform.PAGE_SIZE);
const page_table = vmm.readPageTable();
const space = vmm.AddressSpace.create(page_table, 0);
var i: usize = 0;
while (i < pages) : (i += 1) {
try lockFrame(allocator, vmm.getAddress(space, 0, start + (i * platform.PAGE_SIZE)).?);
}
}
pub fn reserveMultibootMemory(allocator: *FrameAllocator, info: [*c]u8) !void {
const info_tag: *easyboot.multiboot_info_t = @alignCast(@ptrCast(info));
var address: usize = @intFromPtr(info);
var size: usize = info_tag.total_size;
adjustAddressToPageBoundary(&address, &size);
debug.print("Locking multiboot memory at {x}, {d} bytes\n", .{ address, size });
try lockFrames(allocator, address, try std.math.divCeil(usize, size, platform.PAGE_SIZE));
const Context = struct {
allocator: *FrameAllocator,
};
var ctx = Context{ .allocator = allocator };
multiboot.findMultibootTags(easyboot.multiboot_tag_module_t, @ptrCast(info), struct {
fn reserveMemory(mod: *easyboot.multiboot_tag_module_t, context: *const Context) !void {
var mod_address: usize = mod.mod_start;
var mod_size: usize = mod.mod_end - mod.mod_start;
adjustAddressToPageBoundary(&mod_address, &mod_size);
debug.print("Locking memory for module {s} at address {x}, {d} bytes\n", .{ mod.string(), mod_address, mod_size });
try lockFrames(context.allocator, mod_address, try std.math.divCeil(usize, mod_size, platform.PAGE_SIZE));
}
fn handler(mod: *easyboot.multiboot_tag_module_t, context: *const anyopaque) void {
reserveMemory(mod, @alignCast(@ptrCast(context))) catch |err| {
debug.print("Error while reserving multiboot memory {s}: {}\n", .{ mod.string(), err });
while (true) {}
};
}
}.handler, &ctx);
}
var lock: locking.SpinLock = .{};
var global_allocator: *FrameAllocator = undefined;