Support storing in RAM instead of flash

This permits to run without persistent storage. The benefit is that the board
doesn't implement a the syscall API in Tock. The disadvantage is that rebooting
the key will reset the storage.

.github/workflows/cargo_check.yml

@@ -58,6 +58,12 @@ jobs:
           command: check
           args: --target thumbv7em-none-eabi --release --features debug_allocations
 
+      - name: Check OpenSK ram_storage
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+          args: --target thumbv7em-none-eabi --release --features ram_storage
+
       - name: Check OpenSK debug_ctap,with_ctap1
         uses: actions-rs/cargo@v1
         with:

Cargo.toml

@@ -23,6 +23,7 @@ debug_ctap = ["crypto/derive_debug"]
 with_ctap1 = ["crypto/with_ctap1"]
 panic_console = ["libtock/panic_console"]
 debug_allocations = ["libtock/debug_allocations"]
+ram_storage = []
 
 [dev-dependencies]
 elf2tab = "0.4.0"

deploy.py

@@ -405,6 +405,14 @@ if __name__ == "__main__":
             "(i.e. more debug messages will be sent over the console port "
             "such as hexdumps of packets)."),
   )
+  app_commands.add_argument(
+      "--no-persistent-storage",
+      action="append_const",
+      const="ram_storage",
+      dest="features",
+      help=("Compiles and installs the OpenSK application without persistent "
+            "storage (i.e. unplugging the key will reset the key)."),
+  )
   apps_group = app_commands.add_mutually_exclusive_group()
   apps_group.add_argument(
       "--opensk",

run_desktop_tests.sh

@@ -30,6 +30,7 @@ cargo check --release --target=thumbv7em-none-eabi --features with_ctap1
 cargo check --release --target=thumbv7em-none-eabi --features debug_ctap
 cargo check --release --target=thumbv7em-none-eabi --features panic_console
 cargo check --release --target=thumbv7em-none-eabi --features debug_allocations
+cargo check --release --target=thumbv7em-none-eabi --features ram_storage
 cargo check --release --target=thumbv7em-none-eabi --features debug_ctap,with_ctap1
 cargo check --release --target=thumbv7em-none-eabi --features debug_ctap,with_ctap1,panic_console,debug_allocations
 

src/ctap/storage.rs

@@ -21,9 +21,9 @@ use alloc::vec::Vec;
 use core::convert::TryInto;
 use ctap2::embedded_flash::{self, StoreConfig, StoreEntry, StoreError, StoreIndex};
 
-#[cfg(test)]
+#[cfg(any(test, feature = "ram_storage"))]
 type Storage = embedded_flash::BufferStorage;
-#[cfg(not(test))]
+#[cfg(not(any(test, feature = "ram_storage")))]
 type Storage = embedded_flash::SyscallStorage;
 
 // Those constants may be modified before compilation to tune the behavior of the key.
@@ -44,6 +44,9 @@ type Storage = embedded_flash::SyscallStorage;
 // We have: I = ((P - 1) * 4092 - K * S) / 12 * C
 //
 // With P=20 and K=150, we have I > 2M which is enough for 500 increments per day for 10 years.
+#[cfg(feature = "ram_storage")]
+const NUM_PAGES: usize = 2;
+#[cfg(not(feature = "ram_storage"))]
 const NUM_PAGES: usize = 20;
 const MAX_SUPPORTED_RESIDENTIAL_KEYS: usize = 150;
 
@@ -130,10 +133,14 @@ pub struct PersistentStore {
     store: embedded_flash::Store<Storage, Config>,
 }
 
+#[cfg(feature = "ram_storage")]
+const PAGE_SIZE: usize = 0x100;
+#[cfg(not(feature = "ram_storage"))]
 const PAGE_SIZE: usize = 0x1000;
+
 const STORE_SIZE: usize = NUM_PAGES * PAGE_SIZE;
 
-#[cfg(not(test))]
+#[cfg(not(any(test, feature = "ram_storage")))]
 #[link_section = ".app_state"]
 static STORE: [u8; STORE_SIZE] = [0xff; STORE_SIZE];
 
@@ -144,9 +151,9 @@ impl PersistentStore {
     ///
     /// This should be at most one instance of persistent store per program lifetime.
     pub fn new(rng: &mut impl Rng256) -> PersistentStore {
-        #[cfg(not(test))]
+        #[cfg(not(any(test, feature = "ram_storage")))]
         let storage = PersistentStore::new_prod_storage();
-        #[cfg(test)]
+        #[cfg(any(test, feature = "ram_storage"))]
         let storage = PersistentStore::new_test_storage();
         let mut store = PersistentStore {
             store: embedded_flash::Store::new(storage, Config).unwrap(),
@@ -155,7 +162,7 @@ impl PersistentStore {
         store
     }
 
-    #[cfg(not(test))]
+    #[cfg(not(any(test, feature = "ram_storage")))]
     fn new_prod_storage() -> Storage {
         let store = unsafe {
             // Safety: The store cannot alias because this function is called only once.
@@ -167,7 +174,7 @@ impl PersistentStore {
         }
     }
 
-    #[cfg(test)]
+    #[cfg(any(test, feature = "ram_storage"))]
     fn new_test_storage() -> Storage {
         let store = vec![0xff; STORE_SIZE].into_boxed_slice();
         let options = embedded_flash::BufferOptions {

src/embedded_flash/buffer.rs

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 use super::{Index, Storage, StorageError, StorageResult};
+use alloc::boxed::Box;
 
 pub struct BufferStorage {
     storage: Box<[u8]>,
@@ -230,7 +231,7 @@ impl Snapshot {
 
     fn get(&mut self) -> Result<Box<[u8]>, usize> {
         let mut snapshot = Snapshot::Ready;
-        std::mem::swap(self, &mut snapshot);
+        core::mem::swap(self, &mut snapshot);
         match snapshot {
             Snapshot::Armed { delay } => Err(delay),
             Snapshot::Taken { storage } => Ok(storage),

src/embedded_flash/mod.rs

@@ -12,13 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#[cfg(feature = "std")]
 mod buffer;
 mod storage;
 mod store;
 mod syscall;
 
-#[cfg(feature = "std")]
 pub use self::buffer::{BufferOptions, BufferStorage};
 pub use self::storage::{Index, Storage, StorageError, StorageResult};
 pub use self::store::{Store, StoreConfig, StoreEntry, StoreError, StoreIndex};