Standardise and add safety comments.

These will soon be required by a lint.

Bug: 290018030
Test: m rust
Change-Id: If62281a5eb2160061a11f28588b7a14e32ce265b
diff --git a/microdroid_manager/src/dice.rs b/microdroid_manager/src/dice.rs
index bacefcd..8e078ea 100644
--- a/microdroid_manager/src/dice.rs
+++ b/microdroid_manager/src/dice.rs
@@ -78,7 +78,7 @@
         let mmap_size =
             file.read_u64::<NativeEndian>()
                 .map_err(|error| Error::new(error).context("Reading driver"))? as usize;
-        // It's safe to map the driver as the service will only create a single
+        // SAFETY: It's safe to map the driver as the service will only create a single
         // mapping per process.
         let mmap_addr = unsafe {
             let fd = file.as_raw_fd();
@@ -87,10 +87,10 @@
         if mmap_addr == MAP_FAILED {
             bail!("Failed to mmap {:?}", driver_path);
         }
-        // The slice is created for the region of memory that was just
+        let mmap_buf =
+        // SAFETY: The slice is created for the region of memory that was just
         // successfully mapped into the process address space so it will be
         // accessible and not referenced from anywhere else.
-        let mmap_buf =
             unsafe { slice::from_raw_parts((mmap_addr as *const u8).as_ref().unwrap(), mmap_size) };
         let bcc_handover =
             bcc_handover_parse(mmap_buf).map_err(|_| anyhow!("Failed to parse Bcc Handover"))?;
@@ -149,9 +149,9 @@
 impl Drop for DiceDriver<'_> {
     fn drop(&mut self) {
         if let &mut Self::Real { mmap_addr, mmap_size, .. } = self {
-            // All references to the mapped region have the same lifetime as self. Since self is
-            // being dropped, so are all the references to the mapped region meaning its safe to
-            // unmap.
+            // SAFETY: All references to the mapped region have the same lifetime as self. Since
+            // self is being dropped, so are all the references to the mapped region meaning it's
+            // safe to unmap.
             let ret = unsafe { munmap(mmap_addr, mmap_size) };
             if ret != 0 {
                 log::warn!("Failed to munmap ({})", ret);