Merge pull request #389 from 00xc/cpu/tss

cpu/tss: fix TSS layout

Author: joergroedel

kernel/src/cpu/idt/svsm.rs

@@ -57,10 +57,7 @@ extern "C" {
 }
 
 fn init_ist_vectors() {
-    idt_mut().set_entry(
-        DF_VECTOR,
-        IdtEntry::ist_entry(asm_entry_df, IST_DF.try_into().unwrap()),
-    );
+    idt_mut().set_entry(DF_VECTOR, IdtEntry::ist_entry(asm_entry_df, IST_DF.get()));
 }
 
 pub fn early_idt_init() {

kernel/src/cpu/percpu.rs

@@ -499,7 +499,7 @@ impl PerCpu {
     fn setup_tss(&self) {
         let double_fault_stack = self.get_top_of_df_stack();
         let mut tss = self.tss.get();
-        tss.ist_stacks[IST_DF] = double_fault_stack;
+        tss.set_ist_stack(IST_DF, double_fault_stack);
         self.tss.set(tss);
     }
 

kernel/src/cpu/tss.rs

@@ -6,17 +6,18 @@
 
 use super::gdt::GDTEntry;
 use crate::address::VirtAddr;
+use core::num::NonZeroU8;
 
 // IST offsets
-pub const _IST_INVALID: usize = 0;
-pub const IST_DF: usize = 1;
+pub const IST_DF: NonZeroU8 = unsafe { NonZeroU8::new_unchecked(1) };
 
 #[derive(Debug, Default, Clone, Copy)]
-#[repr(C, packed)]
+#[repr(C, packed(4))]
 pub struct X86Tss {
-    reserved1: u32,
+    reserved0: u32,
     pub stacks: [VirtAddr; 3],
-    pub ist_stacks: [VirtAddr; 8],
+    reserved1: u64,
+    ist_stacks: [VirtAddr; 7],
     reserved2: u64,
     reserved3: u16,
     io_bmp_base: u16,
@@ -27,15 +28,22 @@ pub const TSS_LIMIT: u64 = core::mem::size_of::<X86Tss>() as u64;
 impl X86Tss {
     pub const fn new() -> Self {
         X86Tss {
-            reserved1: 0,
+            reserved0: 0,
             stacks: [VirtAddr::null(); 3],
-            ist_stacks: [VirtAddr::null(); 8],
+            reserved1: 0,
+            ist_stacks: [VirtAddr::null(); 7],
             reserved2: 0,
             reserved3: 0,
             io_bmp_base: (TSS_LIMIT + 1) as u16,
         }
     }
 
+    pub fn set_ist_stack(&mut self, index: NonZeroU8, addr: VirtAddr) {
+        // IST entries start at index 1
+        let index = usize::from(index.get() - 1);
+        self.ist_stacks[index] = addr;
+    }
+
     pub fn to_gdt_entry(&self) -> (GDTEntry, GDTEntry) {
         let addr = (self as *const X86Tss) as u64;
 
@@ -60,3 +68,20 @@ impl X86Tss {
         (GDTEntry::from_raw(desc0), GDTEntry::from_raw(desc1))
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use core::mem::offset_of;
+
+    #[test]
+    fn test_tss_offsets() {
+        assert_eq!(offset_of!(X86Tss, reserved0), 0x0);
+        assert_eq!(offset_of!(X86Tss, stacks), 0x4);
+        assert_eq!(offset_of!(X86Tss, reserved1), 0x1c);
+        assert_eq!(offset_of!(X86Tss, ist_stacks), 0x24);
+        assert_eq!(offset_of!(X86Tss, reserved2), 0x5c);
+        assert_eq!(offset_of!(X86Tss, reserved3), 0x64);
+        assert_eq!(offset_of!(X86Tss, io_bmp_base), 0x66);
+    }
+}