From 730df58cc89c8c36e02327378a8d275bd476e52d Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Tue, 24 Sep 2019 16:59:20 -0400
Subject: [PATCH] post-06

---
 Cargo.toml              |  4 +++
 src/gdt.rs              | 45 ++++++++++++++++++++++++++++++
 src/interrupts.rs       | 12 ++++++++
 src/lib.rs              |  2 ++
 src/main.rs             |  3 +-
 tests/stack_overflow.rs | 62 +++++++++++++++++++++++++++++++++++++++++
 6 files changed, 126 insertions(+), 2 deletions(-)
 create mode 100644 src/gdt.rs
 create mode 100644 tests/stack_overflow.rs

diff --git a/Cargo.toml b/Cargo.toml
index fc94f7e..204f961 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -32,4 +32,8 @@ test-success-exit-code = 33         # (0x10 << 1) | 1
 
 [[test]]
 name = "should_panic"
+harness = false
+
+[[test]]
+name = "stack_overflow"
 harness = false
\ No newline at end of file
diff --git a/src/gdt.rs b/src/gdt.rs
new file mode 100644
index 0000000..f8146a9
--- /dev/null
+++ b/src/gdt.rs
@@ -0,0 +1,45 @@
+use lazy_static::lazy_static;
+use x86_64::VirtAddr;
+use x86_64::structures::gdt::{GlobalDescriptorTable, Descriptor, SegmentSelector};
+use x86_64::structures::tss::TaskStateSegment;
+
+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;
+            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
+    };
+}
+
+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 })
+    };
+}
+
+struct Selectors {
+    code_selector: SegmentSelector,
+    tss_selector: SegmentSelector,
+}
+
+pub fn init() {
+    use x86_64::instructions::segmentation::set_cs;
+    use x86_64::instructions::tables::load_tss;
+    GDT.0.load();
+    unsafe {
+        set_cs(GDT.1.code_selector);
+        load_tss(GDT.1.tss_selector);
+    }
+}
\ No newline at end of file
diff --git a/src/interrupts.rs b/src/interrupts.rs
index 7fa4d5e..3adacc5 100644
--- a/src/interrupts.rs
+++ b/src/interrupts.rs
@@ -1,6 +1,7 @@
 use lazy_static::lazy_static;
 use x86_64::structures::idt::{InterruptDescriptorTable, InterruptStackFrame};
 
+use crate::gdt;
 use crate::println;
 
 #[cfg(test)]
@@ -10,6 +11,11 @@ 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
     };
 }
@@ -24,6 +30,12 @@ extern "x86-interrupt" fn breakpoint_handler(
     println!("EXCEPTION: BREAKPOINT\n{:#?}", stack_frame);
 }
 
+extern "x86-interrupt" fn double_fault_handler(
+    stack_frame: &mut InterruptStackFrame, _error_code: u64
+) {
+    panic!("EXCEPTION: DOUBLE FAULT\n{:#?}", stack_frame);
+}
+
 #[test_case]
 fn test_breakpoint_exception() {
     serial_print!("test_breakpoint_exception...");
diff --git a/src/lib.rs b/src/lib.rs
index 395f595..f65c260 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -7,6 +7,7 @@
 
 use core::panic::PanicInfo;
 
+pub mod gdt;
 pub mod interrupts;
 pub mod serial;
 pub mod macros;
@@ -59,5 +60,6 @@ pub fn exit_qemu(exit_code: QemuExitCode) {
 }
 
 pub fn init() {
+    gdt::init();
     interrupts::init_idt();
 }
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 1e32c3f..aa31d6b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -28,10 +28,9 @@ pub extern "C" fn _start() -> ! {
 
     blog_os::init();
 
-    x86_64::instructions::interrupts::int3();
-
     #[cfg(test)]
     test_main();
 
+    println!("It did not crash!");
     loop {}
 }
diff --git a/tests/stack_overflow.rs b/tests/stack_overflow.rs
new file mode 100644
index 0000000..638143a
--- /dev/null
+++ b/tests/stack_overflow.rs
@@ -0,0 +1,62 @@
+// in tests/stack_overflow.rs
+
+#![no_std]
+#![no_main]
+#![feature(abi_x86_interrupt)]
+
+use core::panic::PanicInfo;
+use lazy_static::lazy_static;
+use x86_64::structures::idt::InterruptDescriptorTable;
+use x86_64::structures::idt::InterruptStackFrame;
+
+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(blog_os::gdt::DOUBLE_FAULT_IST_INDEX);
+        }
+
+        idt
+    };
+}
+
+
+use blog_os::{exit_qemu, QemuExitCode, serial_print, serial_println};
+
+#[no_mangle]
+pub extern "C" fn _start() -> ! {
+    serial_print!("stack_overflow... ");
+
+    blog_os::gdt::init();
+    init_test_idt();
+
+    // trigger a stack overflow
+    stack_overflow();
+
+    panic!("Execution continued after stack overflow");
+}
+
+#[panic_handler]
+fn panic(info: &PanicInfo) -> ! {
+    blog_os::test_panic_handler(info)
+}
+
+#[allow(unconditional_recursion)]
+fn stack_overflow() {
+    stack_overflow(); // for each recursion, the return address is pushed
+}
+
+pub fn init_test_idt() {
+    TEST_IDT.load();
+}
+
+extern "x86-interrupt" fn test_double_fault_handler(
+    _stack_frame: &mut InterruptStackFrame,
+    _error_code: u64,
+) {
+    serial_println!("[ok]");
+    exit_qemu(QemuExitCode::Success);
+    loop {}
+}