td-payload: add new shared memory init function with private shadow

To keep the original API behavior unchanged. The extended API init the
shared memory allocator with a private shadow start address. If the
private shadow is not available, the method `copy_to_private_shadow` will
return None.

As the `shadow_start` may be lower or higher than start of shared memory,
the way of allocating private shadow is changed to use the offset of the
allocated shared address to the start of shared allocator.

Signed-off-by: Jiaqi Gao <[email protected]>

td-payload/src/mm/shared.rs

@@ -10,35 +10,38 @@ use super::SIZE_4K;
 use crate::arch::shared::decrypt;
 
 static SHARED_MEMORY_ALLOCATOR: LockedHeap = LockedHeap::empty();
-static SHADOW_OFFSET: Once<usize> = Once::new();
+static SHARED_START: Once<usize> = Once::new();
+static SHADOW_START: Once<usize> = Once::new();
 
 pub fn init_shared_memory(start: u64, size: usize) {
     if size % SIZE_4K != 0 {
         panic!("Failed to initialize shared memory: size needs to be aligned with 0x1000");
     }
-    let shared_size = size / 2;
 
     // Set the shared memory region to be shared
-    decrypt(start, shared_size);
+    decrypt(start, size);
     // Initialize the shared memory allocator
     unsafe {
-        SHARED_MEMORY_ALLOCATOR
-            .lock()
-            .init(start as *mut u8, shared_size);
+        SHARED_MEMORY_ALLOCATOR.lock().init(start as *mut u8, size);
     }
-    SHADOW_OFFSET.call_once(|| shared_size);
+}
+
+pub fn init_shared_memory_with_shadow(start: u64, size: usize, shadow_start: u64) {
+    init_shared_memory(start, size);
+    SHADOW_START.call_once(|| start as usize);
+    SHARED_START.call_once(|| shadow_start as usize);
 }
 
 pub struct SharedMemory {
     addr: usize,
-    shadow_addr: usize,
+    shadow_addr: Option<usize>,
     size: usize,
 }
 
 impl SharedMemory {
     pub fn new(num_page: usize) -> Option<Self> {
         let addr = unsafe { alloc_shared_pages(num_page)? };
-        let shadow_addr = alloc_private_shadow_pages(addr)?;
+        let shadow_addr = alloc_private_shadow_pages(addr);
 
         Some(Self {
             addr,
@@ -47,12 +50,13 @@ impl SharedMemory {
         })
     }
 
-    pub fn copy_to_private_shadow(&mut self) -> &[u8] {
-        let shadow =
-            unsafe { core::slice::from_raw_parts_mut(self.shadow_addr as *mut u8, self.size) };
-        shadow.copy_from_slice(self.as_bytes());
+    pub fn copy_to_private_shadow(&mut self) -> Option<&[u8]> {
+        self.shadow_addr.map(|addr| {
+            let shadow = unsafe { core::slice::from_raw_parts_mut(addr as *mut u8, self.size) };
+            shadow.copy_from_slice(self.as_bytes());
 
-        shadow
+            &shadow[..]
+        })
     }
 
     pub fn as_bytes(&self) -> &[u8] {
@@ -110,5 +114,6 @@ pub unsafe fn free_shared_page(addr: usize) {
 }
 
 fn alloc_private_shadow_pages(shared_addr: usize) -> Option<usize> {
-    Some(shared_addr + SHADOW_OFFSET.get()?)
+    let offset = shared_addr.checked_sub(*SHARED_START.get()?)?;
+    Some(SHADOW_START.get()? + offset)
 }