Handle double faults (#7)

Author: JuozasVainauskas

Cargo.toml

@@ -22,4 +22,8 @@ test-success-exit-code = 33         # (0x10 << 1) | 1
 
 [[test]]
 name = "should_panic"
-harness = false
+harness = false
+
+[[test]]
+name = "stack_overflow"
+harness = false

src/gdt.rs

@@ -0,0 +1,45 @@
+use x86_64::VirtAddr;
+use x86_64::structures::tss::TaskStateSegment;
+use x86_64::structures::gdt::{GlobalDescriptorTable, Descriptor, SegmentSelector};
+use lazy_static::lazy_static;
+
+pub const DOUBLE_FAULT_IST_INDEX: u16 = 0;
+
+lazy_static! {
+    static ref TSS: TaskStateSegment = {
+        let mut tss = TaskStateSegment::new();
+        tss.interrupt_stack_table[DOUBLE_FAULT_IST_INDEX as usize] = {
+            const STACK_SIZE: usize = 4096 * 5;
+            static mut STACK: [u8; STACK_SIZE] = [0; STACK_SIZE];
+
+            let stack_start = VirtAddr::from_ptr(unsafe { &STACK });
+            let stack_end = stack_start + STACK_SIZE;
+            stack_end
+        };
+        tss
+    };
+}
+
+struct Selectors {
+    code_selector: SegmentSelector,
+    tss_selector: SegmentSelector,
+}
+
+lazy_static! {
+    static ref GDT: (GlobalDescriptorTable, Selectors) = {
+        let mut gdt = GlobalDescriptorTable::new();
+        let code_selector = gdt.add_entry(Descriptor::kernel_code_segment());
+        let tss_selector = gdt.add_entry(Descriptor::tss_segment(&TSS));
+        (gdt, Selectors { code_selector, tss_selector })
+    };
+}
+
+pub fn init() {
+    use x86_64::instructions::tables::load_tss;
+    use x86_64::instructions::segmentation::{CS, Segment};
+    GDT.0.load();
+    unsafe {
+        CS::set_reg(GDT.1.code_selector);
+        load_tss(GDT.1.tss_selector);
+    }
+}

src/interrupts.rs

@@ -1,11 +1,16 @@
 use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
 use crate::println;
+use crate::gdt;
 use lazy_static::lazy_static;
 
 lazy_static! {
     static ref IDT: InterruptDescriptorTable = {
         let mut idt = InterruptDescriptorTable::new();
         idt.breakpoint.set_handler_fn(breakpoint_handler);
+        unsafe {
+            idt.double_fault.set_handler_fn(double_fault_handler)
+                .set_stack_index(gdt::DOUBLE_FAULT_IST_INDEX);
+        }
         idt
     };
 }
@@ -18,6 +23,10 @@ extern "x86-interrupt" fn breakpoint_handler(stack_frame: InterruptStackFrame) {
     println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
 }
 
+extern "x86-interrupt" fn double_fault_handler(stack_frame: InterruptStackFrame, _error_code: u64) -> ! {
+    panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
+}
+
 #[test_case]
 fn test_breakpoint_exceptions() {
     x86_64::instructions::interrupts::int3();

src/lib.rs

@@ -10,8 +10,10 @@ use core::panic::PanicInfo;
 pub mod serial;
 pub mod vga_buffer;
 pub mod interrupts;
+pub mod gdt;
 
 pub fn init() {
+    gdt::init();
     interrupts::init_idt();
 }
 

src/main.rs

@@ -21,8 +21,6 @@ pub extern "C" fn _start() -> ! {
 
     os::init();
 
-    x86_64::instructions::interrupts::int3();
-
     #[cfg(test)]
     test_main();
 

tests/stack_overflow.rs

@@ -0,0 +1,55 @@
+#![feature(abi_x86_interrupt)]
+#![no_std]
+#![no_main]
+
+use core::panic::PanicInfo;
+use os::{exit_qemu, QemuExitCode, serial_println, serial_print};
+use lazy_static::lazy_static;
+use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
+
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    serial_print!("stack_overflow::stack_overflow...\t");
+    os::gdt::init();
+    init_test_idt();
+    stack_overflow();
+
+    panic!("Execution continued after stack overflow");
+}
+
+lazy_static! {
+    static ref TEST_IDT: InterruptDescriptorTable = {
+        let mut idt = InterruptDescriptorTable::new();
+        unsafe {
+            idt.double_fault
+                .set_handler_fn(test_double_fault_handler)
+                .set_stack_index(os::gdt::DOUBLE_FAULT_IST_INDEX);
+        }
+
+        idt
+    };
+}
+
+extern "x86-interrupt" fn test_double_fault_handler(_stack_frame: InterruptStackFrame, _error_code: u64) -> ! {
+    serial_println!("[ok]");
+    exit_qemu(QemuExitCode::Success);
+    loop {}
+}
+
+pub fn init_test_idt() {
+    TEST_IDT.load();
+}
+
+#[allow(unconditional_recursion)]
+fn stack_overflow() {
+    // for each recursion, the return address is pushed
+    stack_overflow();
+
+    // prevent tail recursion optimizations
+    volatile::Volatile::new(0).read();
+}
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    os::test_panic_handler(info);
+}