xmr: manual BP serialization

- more memory effective as the memory is critical in the range proof section

src/apps/monero/controller/misc.py

@@ -73,6 +73,50 @@ def dump_msg_gc(msg, preallocate=None, msg_type=None, del_msg=False):
     return b
 
 
+def dump_rsig_bp(rsig):
+    from trezor.utils import memcpy
+
+    if len(rsig.L) > 127:
+        raise ValueError("Too large")
+
+    # Manual serialization as the generic purpose misc.dump_msg_gc
+    # is more memory intensive which is not desired in the range proof section.
+
+    # BP: V, A, S, T1, T2, taux, mu, L, R, a, b, t
+    # Commitment vector V is not serialized
+    # Vector size under 127 thus varint occupies 1 B
+    buff_size = 32 * (9 + 2 * (len(rsig.L))) + 2
+    buff = bytearray(buff_size)
+
+    memcpy(buff, 0, rsig.A, 0, 32)
+    memcpy(buff, 32, rsig.S, 0, 32)
+    memcpy(buff, 32 * 2, rsig.T1, 0, 32)
+    memcpy(buff, 32 * 3, rsig.T2, 0, 32)
+    memcpy(buff, 32 * 4, rsig.taux, 0, 32)
+    memcpy(buff, 32 * 5, rsig.mu, 0, 32)
+
+    buff[32 * 6] = len(rsig.L)
+    offset = 32 * 6 + 1
+
+    for x in rsig.L:
+        memcpy(buff, offset, x, 0, 32)
+        offset += 32
+
+    buff[offset] = len(rsig.R)
+    offset += 1
+
+    for x in rsig.R:
+        memcpy(buff, offset, x, 0, 32)
+        offset += 32
+
+    memcpy(buff, offset, rsig.a, 0, 32)
+    offset += 32
+    memcpy(buff, offset, rsig.b, 0, 32)
+    offset += 32
+    memcpy(buff, offset, rsig.t, 0, 32)
+    return buff
+
+
 def dst_entry_to_stdobj(dst):
     if dst is None:
         return None

src/apps/monero/protocol/tsx_sign_builder.py

@@ -924,9 +924,7 @@ def _range_proof(self, idx, amount, rsig_data=None):
             self.full_message_hasher.rsig_val(rsig, True, raw=False)
             self._mem_trace("post-bp-hash" if __debug__ else None, collect=True)
 
-            rsig = misc.dump_msg_gc(
-                rsig, preallocate=ring_ct.bp_size(batch_size) + 8, del_msg=True
-            )
+            rsig = misc.dump_rsig_bp(rsig)
             self._mem_trace(
                 "post-bp-ser, size: %s" % len(rsig) if __debug__ else None, collect=True
             )