Allow cloning of kernel threads. Userspace breaks potentially due to stack aliasing

arch/x86_64/src/context.rs

@@ -6,7 +6,7 @@ use core::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
 /// This must be done, as no locks can be held on the stack during switch
 pub static CONTEXT_SWITCH_LOCK: AtomicBool = ATOMIC_BOOL_INIT;
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 pub struct Context {
     /// Page table pointer
     cr3: usize,
@@ -96,5 +96,7 @@ impl Context {
 
         // Unset global lock, set inside of kernel
         CONTEXT_SWITCH_LOCK.store(false, Ordering::SeqCst);
+
+        asm!("xchg bx, bx" : : : : "intel", "volatile");
     }
 }

arch/x86_64/src/interrupt/syscall.rs

@@ -3,7 +3,7 @@ pub unsafe extern fn syscall() {
     #[inline(never)]
     unsafe fn inner() {
         extern {
-            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize) -> usize;
+            fn syscall(a: usize, b: usize, c: usize, d: usize, e: usize, f: usize, stack: usize) -> usize;
         }
 
         let mut a;
@@ -13,10 +13,11 @@ pub unsafe extern fn syscall() {
             let d;
             let e;
             let f;
-            asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f)
+            let stack;
+            asm!("" : "={rax}"(a), "={rbx}"(b), "={rcx}"(c), "={rdx}"(d), "={rsi}"(e), "={rdi}"(f), "={rbp}"(stack)
                 : : : "intel", "volatile");
 
-            a = syscall(a, b, c, d, e, f);
+            a = syscall(a, b, c, d, e, f, stack);
         }
 
         asm!("" : : "{rax}"(a) : : "intel", "volatile");
@@ -36,3 +37,10 @@ pub unsafe extern fn syscall() {
         iretq"
         : : : : "intel", "volatile");
 }
+
+#[naked]
+pub unsafe extern fn clone_ret() -> usize {
+    asm!("pop rbp"
+        : : : : "intel", "volatile");
+        0
+}

arch/x86_64/src/start.rs

@@ -187,8 +187,7 @@ pub unsafe extern fn kstart_ap(cpu_id: usize, page_table: usize, stack_start: us
 
 pub unsafe fn usermode(ip: usize, sp: usize) -> ! {
     // Go to usermode
-    asm!("xchg bx, bx
-        mov ds, ax
+    asm!("mov ds, ax
         mov es, ax
         mov fs, ax
         mov gs, ax
@@ -201,7 +200,7 @@ pub unsafe fn usermode(ip: usize, sp: usize) -> ! {
         : // No output because it never returns
         :   "{rax}"(gdt::GDT_USER_DATA << 3 | 3), // Stack segment
             "{rbx}"(sp), // Stack pointer
-            "{rcx}"(3 << 12 | 1 << 9), // Flags - Set IOPL and interrupt enable flag
+            "{rcx}"(3 << 12/* | 1 << 9*/), // Flags - Set IOPL and interrupt enable flag
             "{rdx}"(gdt::GDT_USER_CODE << 3 | 3), // Code segment
             "{rsi}"(ip) // IP
         : // No clobers because it never returns