feat(keystore): sealed real/duress slots (argon2id 16MiB/3, ChaCha20-Poly1305), torn-write-safe 2-copy record, wipe state; virtio-rng driver + Entropy port; RustCrypto deps

crates/hw-virtio/src/mmio.rs

@@ -29,6 +29,7 @@ pub const STATUS_DRIVER: u32 = 2;
 pub const STATUS_DRIVER_OK: u32 = 4;
 
 pub const DEVICE_ID_BLOCK: u32 = 2;
+pub const DEVICE_ID_RNG: u32 = 4;
 pub const DEVICE_ID_GPU: u32 = 16;
 pub const DEVICE_ID_INPUT: u32 = 18;
 

crates/hw-virtio/src/queue.rs

@@ -28,8 +28,14 @@ impl VirtioQueue {
 
     /// Hands the device a chain of `descs` and waits until it is used.
     pub fn submit(&self, mmio: &impl MmioAccess, descs: &[Descriptor]) -> bool {
+        self.submit_written(mmio, descs).is_some()
+    }
+
+    /// Like `submit`; how many bytes the device wrote into the chain's
+    /// writable buffers (it may write fewer than they hold).
+    pub fn submit_written(&self, mmio: &impl MmioAccess, descs: &[Descriptor]) -> Option<u32> {
         if descs.is_empty() || descs.len() > QUEUE_SIZE {
-            return false;
+            return None;
         }
         let r = &self.rings;
         for (i, d) in descs.iter().enumerate() {
@@ -56,9 +62,11 @@ impl VirtioQueue {
             core::hint::spin_loop();
             timeout -= 1;
             if timeout == 0 {
-                return false;
+                return None;
             }
         }
-        true
+        // The used element just added: the chain's head id, then its length.
+        let element = USED + 4 + (avail_idx as usize % QUEUE_SIZE) * 8;
+        Some(r.read::<u32>(element + 4))
     }
 }