From e942f8e40d6f9bc629c62bcdc2d2c27215640e13 Mon Sep 17 00:00:00 2001
From: tychovrahe <brunam@seznam.cz>
Date: Tue, 3 Dec 2024 19:41:31 +0100
Subject: [PATCH 1/5] refactor(core): split polling can_read and reading from
 USB

[no changelog]
---
 .../upymod/modtrezorio/modtrezorio-hid.h      | 15 ++++++++++
 .../upymod/modtrezorio/modtrezorio-poll.h     | 21 ++++----------
 .../upymod/modtrezorio/modtrezorio-webusb.h   | 15 ++++++++++
 core/mocks/generated/trezorio/__init__.pyi    | 10 +++++++
 core/src/apps/webauthn/fido2.py               | 12 ++++++--
 core/src/trezor/wire/codec/codec_v1.py        | 12 ++++++--
 core/tests/test_trezor.wire.codec.codec_v1.py | 28 +++++++++++++------
 7 files changed, 85 insertions(+), 28 deletions(-)

diff --git a/core/embed/upymod/modtrezorio/modtrezorio-hid.h b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
index bcf141d7765..cedc2b437d2 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-hid.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
@@ -141,6 +141,20 @@ STATIC mp_obj_t mod_trezorio_HID_write(mp_obj_t self, mp_obj_t msg) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_HID_write_obj,
                                  mod_trezorio_HID_write);
 
+/// def read(self, buf: bytes) -> int:
+///     """
+///     Reads message using USB HID (device) or UDP (emulator).
+///     """
+STATIC mp_obj_t mod_trezorio_HID_read(mp_obj_t self, mp_obj_t buffer) {
+  mp_obj_HID_t *o = MP_OBJ_TO_PTR(self);
+  mp_buffer_info_t buf = {0};
+  mp_get_buffer_raise(buffer, &buf, MP_BUFFER_WRITE);
+  ssize_t r = usb_hid_read(o->info.iface_num, buf.buf, buf.len);
+  return MP_OBJ_NEW_SMALL_INT(r);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_HID_read_obj,
+                                 mod_trezorio_HID_read);
+
 /// def write_blocking(self, msg: bytes, timeout_ms: int) -> int:
 ///     """
 ///     Sends message using USB HID (device) or UDP (emulator).
@@ -162,6 +176,7 @@ STATIC const mp_rom_map_elem_t mod_trezorio_HID_locals_dict_table[] = {
     {MP_ROM_QSTR(MP_QSTR_iface_num),
      MP_ROM_PTR(&mod_trezorio_HID_iface_num_obj)},
     {MP_ROM_QSTR(MP_QSTR_write), MP_ROM_PTR(&mod_trezorio_HID_write_obj)},
+    {MP_ROM_QSTR(MP_QSTR_read), MP_ROM_PTR(&mod_trezorio_HID_read_obj)},
     {MP_ROM_QSTR(MP_QSTR_write_blocking),
      MP_ROM_PTR(&mod_trezorio_HID_write_blocking_obj)},
 };
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-poll.h b/core/embed/upymod/modtrezorio/modtrezorio-poll.h
index 2d97e491e7f..3e0a738abdb 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-poll.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-poll.h
@@ -166,22 +166,11 @@ STATIC mp_obj_t mod_trezorio_poll(mp_obj_t ifaces, mp_obj_t list_ref,
       }
 #endif
       else if (mode == POLL_READ) {
-        if (sectrue == usb_hid_can_read(iface)) {
-          uint8_t buf[64] = {0};
-          int len = usb_hid_read(iface, buf, sizeof(buf));
-          if (len > 0) {
-            ret->items[0] = MP_OBJ_NEW_SMALL_INT(i);
-            ret->items[1] = mp_obj_new_bytes(buf, len);
-            return mp_const_true;
-          }
-        } else if (sectrue == usb_webusb_can_read(iface)) {
-          uint8_t buf[64] = {0};
-          int len = usb_webusb_read(iface, buf, sizeof(buf));
-          if (len > 0) {
-            ret->items[0] = MP_OBJ_NEW_SMALL_INT(i);
-            ret->items[1] = mp_obj_new_bytes(buf, len);
-            return mp_const_true;
-          }
+        if ((sectrue == usb_hid_can_read(iface)) ||
+            (sectrue == usb_webusb_can_read(iface))) {
+          ret->items[0] = MP_OBJ_NEW_SMALL_INT(i);
+          ret->items[1] = MP_OBJ_NEW_SMALL_INT(64);
+          return mp_const_true;
         }
       } else if (mode == POLL_WRITE) {
         if (sectrue == usb_hid_can_write(iface)) {
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
index d893b107172..4773be07641 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
@@ -127,10 +127,25 @@ STATIC mp_obj_t mod_trezorio_WebUSB_write(mp_obj_t self, mp_obj_t msg) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_WebUSB_write_obj,
                                  mod_trezorio_WebUSB_write);
 
+/// def read(self, buf: bytes) -> int:
+///     """
+///     Reads message using WebUSB (device) or UDP (emulator).
+///     """
+STATIC mp_obj_t mod_trezorio_WebUSB_read(mp_obj_t self, mp_obj_t buffer) {
+  mp_obj_HID_t *o = MP_OBJ_TO_PTR(self);
+  mp_buffer_info_t buf = {0};
+  mp_get_buffer_raise(buffer, &buf, MP_BUFFER_WRITE);
+  ssize_t r = usb_webusb_read(o->info.iface_num, buf.buf, buf.len);
+  return MP_OBJ_NEW_SMALL_INT(r);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_WebUSB_read_obj,
+                                 mod_trezorio_WebUSB_read);
+
 STATIC const mp_rom_map_elem_t mod_trezorio_WebUSB_locals_dict_table[] = {
     {MP_ROM_QSTR(MP_QSTR_iface_num),
      MP_ROM_PTR(&mod_trezorio_WebUSB_iface_num_obj)},
     {MP_ROM_QSTR(MP_QSTR_write), MP_ROM_PTR(&mod_trezorio_WebUSB_write_obj)},
+    {MP_ROM_QSTR(MP_QSTR_read), MP_ROM_PTR(&mod_trezorio_WebUSB_read_obj)},
 };
 STATIC MP_DEFINE_CONST_DICT(mod_trezorio_WebUSB_locals_dict,
                             mod_trezorio_WebUSB_locals_dict_table);
diff --git a/core/mocks/generated/trezorio/__init__.pyi b/core/mocks/generated/trezorio/__init__.pyi
index efb11e08e96..8f34d9d1f01 100644
--- a/core/mocks/generated/trezorio/__init__.pyi
+++ b/core/mocks/generated/trezorio/__init__.pyi
@@ -32,6 +32,11 @@ class HID:
         Sends message using USB HID (device) or UDP (emulator).
         """
 
+    def read(self, buf: bytes) -> int:
+        """
+        Reads message using USB HID (device) or UDP (emulator).
+        """
+
     def write_blocking(self, msg: bytes, timeout_ms: int) -> int:
         """
         Sends message using USB HID (device) or UDP (emulator).
@@ -148,6 +153,11 @@ class WebUSB:
         """
         Sends message using USB WebUSB (device) or UDP (emulator).
         """
+
+    def read(self, buf: bytes) -> int:
+        """
+        Reads message using WebUSB (device) or UDP (emulator).
+        """
 from . import fatfs, haptic, sdcard
 POLL_READ: int  # wait until interface is readable and return read data
 POLL_WRITE: int  # wait until interface is writable
diff --git a/core/src/apps/webauthn/fido2.py b/core/src/apps/webauthn/fido2.py
index 5a1bedd4ae7..2125ec86997 100644
--- a/core/src/apps/webauthn/fido2.py
+++ b/core/src/apps/webauthn/fido2.py
@@ -376,7 +376,11 @@ async def _read_cmd(iface: HID) -> Cmd | None:
     read = loop.wait(iface.iface_num() | io.POLL_READ)
 
     # wait for incoming command indefinitely
-    buf = await read
+    msg_len = await read
+    buf = bytearray(msg_len)
+    read_len = iface.read(buf)
+    if read_len != msg_len:
+        raise ValueError("Invalid length")
     while True:
         ifrm = overlay_struct(bytearray(buf), desc_init)
         bcnt = ifrm.bcnt
@@ -415,7 +419,11 @@ async def _read_cmd(iface: HID) -> Cmd | None:
         read.timeout_ms = _CTAP_HID_TIMEOUT_MS
         while datalen < bcnt:
             try:
-                buf = await read
+                msg_len = await read
+                buf = bytearray(msg_len)
+                read_len = iface.read(buf)
+                if read_len != msg_len:
+                    raise ValueError("Invalid length")
             except loop.Timeout:
                 if __debug__:
                     warning(__name__, "_ERR_MSG_TIMEOUT")
diff --git a/core/src/trezor/wire/codec/codec_v1.py b/core/src/trezor/wire/codec/codec_v1.py
index 02ff37f0eaf..68a2797ff56 100644
--- a/core/src/trezor/wire/codec/codec_v1.py
+++ b/core/src/trezor/wire/codec/codec_v1.py
@@ -25,7 +25,11 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
     read = loop.wait(iface.iface_num() | io.POLL_READ)
 
     # wait for initial report
-    report = await read
+    msg_len = await read
+    report = bytearray(msg_len)
+    read_len = iface.read(report)
+    if read_len != msg_len:
+        raise CodecError("Invalid length")
     if report[0] != _REP_MARKER:
         raise CodecError("Invalid magic")
     _, magic1, magic2, mtype, msize = ustruct.unpack(_REP_INIT, report)
@@ -50,7 +54,11 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
 
     while nread < msize:
         # wait for continuation report
-        report = await read
+        msg_len = await read
+        report = bytearray(msg_len)
+        read_len = iface.read(report)
+        if read_len != msg_len:
+            raise CodecError("Invalid length")
         if report[0] != _REP_MARKER:
             raise CodecError("Invalid magic")
 
diff --git a/core/tests/test_trezor.wire.codec.codec_v1.py b/core/tests/test_trezor.wire.codec.codec_v1.py
index 78675859e2c..5a73467e258 100644
--- a/core/tests/test_trezor.wire.codec.codec_v1.py
+++ b/core/tests/test_trezor.wire.codec.codec_v1.py
@@ -12,6 +12,7 @@ class MockHID:
     def __init__(self, num):
         self.num = num
         self.data = []
+        self.packet = None
 
     def iface_num(self):
         return self.num
@@ -20,6 +21,17 @@ def write(self, msg):
         self.data.append(bytearray(msg))
         return len(msg)
 
+    def mock_read(self, packet, gen):
+        self.packet = packet
+        return gen.send(len(packet))
+
+    def read(self, buffer):
+        if self.packet is None:
+            raise Exception("No packet to read")
+        buffer[:] = self.packet
+        self.packet = None
+        return len(buffer)
+
     def wait_object(self, mode):
         return wait(mode | self.num)
 
@@ -48,7 +60,7 @@ def test_read_one_packet(self):
         self.assertObjectEqual(query, self.interface.wait_object(io.POLL_READ))
 
         with self.assertRaises(StopIteration) as e:
-            gen.send(message_packet)
+            self.interface.mock_read(message_packet, gen)
 
         # e.value is StopIteration. e.value.value is the return value of the call
         result = e.value.value
@@ -74,11 +86,11 @@ def test_read_many_packets(self):
         query = gen.send(None)
         for packet in packets[:-1]:
             self.assertObjectEqual(query, self.interface.wait_object(io.POLL_READ))
-            query = gen.send(packet)
+            query = self.interface.mock_read(packet, gen)
 
         # last packet will stop
         with self.assertRaises(StopIteration) as e:
-            gen.send(packets[-1])
+            self.interface.mock_read(packets[-1], gen)
 
         # e.value is StopIteration. e.value.value is the return value of the call
         result = e.value.value
@@ -103,7 +115,7 @@ def test_read_large_message(self):
         query = gen.send(None)
         self.assertObjectEqual(query, self.interface.wait_object(io.POLL_READ))
         with self.assertRaises(StopIteration) as e:
-            gen.send(packet)
+            self.interface.mock_read(packet, gen)
 
         # e.value is StopIteration. e.value.value is the return value of the call
         result = e.value.value
@@ -169,10 +181,10 @@ def test_roundtrip(self):
         query = gen.send(None)
         for packet in self.interface.data[:-1]:
             self.assertObjectEqual(query, self.interface.wait_object(io.POLL_READ))
-            query = gen.send(packet)
+            query = self.interface.mock_read(packet, gen)
 
         with self.assertRaises(StopIteration) as e:
-            gen.send(self.interface.data[-1])
+            self.interface.mock_read(self.interface.data[-1], gen)
 
         result = e.value.value
         self.assertEqual(result.type, MESSAGE_TYPE)
@@ -194,10 +206,10 @@ def test_read_huge_packet(self):
         query = gen.send(None)
         for _ in range(PACKET_COUNT - 1):
             self.assertObjectEqual(query, self.interface.wait_object(io.POLL_READ))
-            query = gen.send(packet)
+            query = self.interface.mock_read(packet, gen)
 
         with self.assertRaises(codec_v1.CodecError) as e:
-            gen.send(packet)
+            self.interface.mock_read(packet,gen)
 
         self.assertEqual(e.value.args[0], "Message too large")
 

From 51556ef6ba7632ecda7feb7e9e816dea1ce02d09 Mon Sep 17 00:00:00 2001
From: tychovrahe <brunam@seznam.cz>
Date: Wed, 4 Dec 2024 10:21:06 +0100
Subject: [PATCH 2/5] fixup! refactor(core): split polling can_read and reading
 from USB

---
 core/embed/io/usb/unix/usb.c                  | 66 ++++++++++++++-----
 .../upymod/modtrezorio/modtrezorio-hid.h      | 28 +++++---
 .../upymod/modtrezorio/modtrezorio-webusb.h   | 26 ++++++--
 core/mocks/generated/trezorio/__init__.pyi    |  6 +-
 core/src/apps/webauthn/fido2.py               |  4 +-
 core/src/trezor/wire/codec/codec_v1.py        |  5 +-
 6 files changed, 97 insertions(+), 38 deletions(-)

diff --git a/core/embed/io/usb/unix/usb.c b/core/embed/io/usb/unix/usb.c
index 8ab0d1087bc..e58f513904d 100644
--- a/core/embed/io/usb/unix/usb.c
+++ b/core/embed/io/usb/unix/usb.c
@@ -50,6 +50,8 @@ static struct {
   int sock;
   struct sockaddr_in si_me, si_other;
   socklen_t slen;
+  uint8_t msg[64];
+  int msg_len;
 } usb_ifaces[USBD_MAX_NUM_INTERFACES];
 
 secbool usb_init(const usb_dev_info_t *dev_info) {
@@ -60,7 +62,9 @@ secbool usb_init(const usb_dev_info_t *dev_info) {
     usb_ifaces[i].sock = -1;
     memzero(&usb_ifaces[i].si_me, sizeof(struct sockaddr_in));
     memzero(&usb_ifaces[i].si_other, sizeof(struct sockaddr_in));
+    memzero(&usb_ifaces[i].msg, sizeof(usb_ifaces[i].msg));
     usb_ifaces[i].slen = 0;
+    usb_ifaces[i].msg_len = 0;
   }
   return sectrue;
 }
@@ -136,36 +140,66 @@ secbool usb_vcp_add(const usb_vcp_info_t *info) {
   return sectrue;
 }
 
-static secbool usb_emulated_poll(uint8_t iface_num, short dir) {
+static secbool usb_emulated_poll_read(uint8_t iface_num) {
   struct pollfd fds[] = {
-      {usb_ifaces[iface_num].sock, dir, 0},
+      {usb_ifaces[iface_num].sock, POLLIN, 0},
   };
-  int r = poll(fds, 1, 0);
-  return sectrue * (r > 0);
-}
+  int res = poll(fds, 1, 0);
+
+  if (res <= 0) {
+    return secfalse;
+  }
 
-static int usb_emulated_read(uint8_t iface_num, uint8_t *buf, uint32_t len) {
   struct sockaddr_in si;
   socklen_t sl = sizeof(si);
-  ssize_t r = recvfrom(usb_ifaces[iface_num].sock, buf, len, MSG_DONTWAIT,
+  ssize_t r = recvfrom(usb_ifaces[iface_num].sock, usb_ifaces[iface_num].msg,
+                       sizeof(usb_ifaces[iface_num].msg), MSG_DONTWAIT,
                        (struct sockaddr *)&si, &sl);
-  if (r < 0) {
-    return r;
+  if (r <= 0) {
+    return secfalse;
   }
+
   usb_ifaces[iface_num].si_other = si;
   usb_ifaces[iface_num].slen = sl;
   static const char *ping_req = "PINGPING";
   static const char *ping_resp = "PONGPONG";
-  if (r == strlen(ping_req) && 0 == memcmp(ping_req, buf, strlen(ping_req))) {
+  if (r == strlen(ping_req) &&
+      0 == memcmp(ping_req, usb_ifaces[iface_num].msg, strlen(ping_req))) {
     if (usb_ifaces[iface_num].slen > 0) {
       sendto(usb_ifaces[iface_num].sock, ping_resp, strlen(ping_resp),
              MSG_DONTWAIT,
              (const struct sockaddr *)&usb_ifaces[iface_num].si_other,
              usb_ifaces[iface_num].slen);
     }
-    return 0;
+    memzero(usb_ifaces[iface_num].msg, sizeof(usb_ifaces[iface_num].msg));
+    return secfalse;
   }
-  return r;
+
+  usb_ifaces[iface_num].msg_len = r;
+
+  return sectrue;
+}
+
+static secbool usb_emulated_poll_write(uint8_t iface_num) {
+  struct pollfd fds[] = {
+      {usb_ifaces[iface_num].sock, POLLOUT, 0},
+  };
+  int r = poll(fds, 1, 0);
+  return sectrue * (r > 0);
+}
+
+static int usb_emulated_read(uint8_t iface_num, uint8_t *buf, uint32_t len) {
+  if (usb_ifaces[iface_num].msg_len > 0) {
+    if (usb_ifaces[iface_num].msg_len < len) {
+      len = usb_ifaces[iface_num].msg_len;
+    }
+    memcpy(buf, usb_ifaces[iface_num].msg, len);
+    usb_ifaces[iface_num].msg_len = 0;
+    memzero(usb_ifaces[iface_num].msg, sizeof(usb_ifaces[iface_num].msg));
+    return len;
+  }
+
+  return 0;
 }
 
 static int usb_emulated_write(uint8_t iface_num, const uint8_t *buf,
@@ -184,7 +218,7 @@ secbool usb_hid_can_read(uint8_t iface_num) {
       usb_ifaces[iface_num].type != USB_IFACE_TYPE_HID) {
     return secfalse;
   }
-  return usb_emulated_poll(iface_num, POLLIN);
+  return usb_emulated_poll_read(iface_num);
 }
 
 secbool usb_webusb_can_read(uint8_t iface_num) {
@@ -192,7 +226,7 @@ secbool usb_webusb_can_read(uint8_t iface_num) {
       usb_ifaces[iface_num].type != USB_IFACE_TYPE_WEBUSB) {
     return secfalse;
   }
-  return usb_emulated_poll(iface_num, POLLIN);
+  return usb_emulated_poll_read(iface_num);
 }
 
 secbool usb_hid_can_write(uint8_t iface_num) {
@@ -200,7 +234,7 @@ secbool usb_hid_can_write(uint8_t iface_num) {
       usb_ifaces[iface_num].type != USB_IFACE_TYPE_HID) {
     return secfalse;
   }
-  return usb_emulated_poll(iface_num, POLLOUT);
+  return usb_emulated_poll_write(iface_num);
 }
 
 secbool usb_webusb_can_write(uint8_t iface_num) {
@@ -208,7 +242,7 @@ secbool usb_webusb_can_write(uint8_t iface_num) {
       usb_ifaces[iface_num].type != USB_IFACE_TYPE_WEBUSB) {
     return secfalse;
   }
-  return usb_emulated_poll(iface_num, POLLOUT);
+  return usb_emulated_poll_write(iface_num);
 }
 
 int usb_hid_read(uint8_t iface_num, uint8_t *buf, uint32_t len) {
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-hid.h b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
index cedc2b437d2..9b6e7c0a375 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-hid.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
@@ -141,19 +141,31 @@ STATIC mp_obj_t mod_trezorio_HID_write(mp_obj_t self, mp_obj_t msg) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_HID_write_obj,
                                  mod_trezorio_HID_write);
 
-/// def read(self, buf: bytes) -> int:
+/// def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
 ///     """
-///     Reads message using USB HID (device) or UDP (emulator).
+///     Reads message using HID (device) or UDP (emulator).
 ///     """
-STATIC mp_obj_t mod_trezorio_HID_read(mp_obj_t self, mp_obj_t buffer) {
-  mp_obj_HID_t *o = MP_OBJ_TO_PTR(self);
+STATIC mp_obj_t mod_trezorio_HID_read(size_t n_args, const mp_obj_t *args) {
+  mp_obj_HID_t *o = MP_OBJ_TO_PTR(args[0]);
   mp_buffer_info_t buf = {0};
-  mp_get_buffer_raise(buffer, &buf, MP_BUFFER_WRITE);
-  ssize_t r = usb_hid_read(o->info.iface_num, buf.buf, buf.len);
+  mp_get_buffer_raise(args[1], &buf, MP_BUFFER_WRITE);
+
+  int offset = mp_obj_get_int(args[2]);
+
+  int len = buf.len - offset;
+  if (n_args >= 3) {
+    int limit = mp_obj_get_int(args[3]);
+    if ((limit - offset) < len) {
+      len = (limit - offset);
+    }
+  }
+
+  ssize_t r =
+      usb_hid_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], len);
   return MP_OBJ_NEW_SMALL_INT(r);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_HID_read_obj,
-                                 mod_trezorio_HID_read);
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_HID_read_obj, 3, 4,
+                                           mod_trezorio_HID_read);
 
 /// def write_blocking(self, msg: bytes, timeout_ms: int) -> int:
 ///     """
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
index 4773be07641..bb3c639f14a 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
@@ -127,19 +127,31 @@ STATIC mp_obj_t mod_trezorio_WebUSB_write(mp_obj_t self, mp_obj_t msg) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_WebUSB_write_obj,
                                  mod_trezorio_WebUSB_write);
 
-/// def read(self, buf: bytes) -> int:
+/// def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
 ///     """
 ///     Reads message using WebUSB (device) or UDP (emulator).
 ///     """
-STATIC mp_obj_t mod_trezorio_WebUSB_read(mp_obj_t self, mp_obj_t buffer) {
-  mp_obj_HID_t *o = MP_OBJ_TO_PTR(self);
+STATIC mp_obj_t mod_trezorio_WebUSB_read(size_t n_args, const mp_obj_t *args) {
+  mp_obj_WebUSB_t *o = MP_OBJ_TO_PTR(args[0]);
   mp_buffer_info_t buf = {0};
-  mp_get_buffer_raise(buffer, &buf, MP_BUFFER_WRITE);
-  ssize_t r = usb_webusb_read(o->info.iface_num, buf.buf, buf.len);
+  mp_get_buffer_raise(args[1], &buf, MP_BUFFER_WRITE);
+
+  int offset = mp_obj_get_int(args[2]);
+
+  int len = buf.len - offset;
+  if (n_args >= 3) {
+    int limit = mp_obj_get_int(args[3]);
+    if ((limit - offset) < len) {
+      len = (limit - offset);
+    }
+  }
+
+  ssize_t r =
+      usb_webusb_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], len);
   return MP_OBJ_NEW_SMALL_INT(r);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_WebUSB_read_obj,
-                                 mod_trezorio_WebUSB_read);
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_WebUSB_read_obj, 3, 4,
+                                           mod_trezorio_WebUSB_read);
 
 STATIC const mp_rom_map_elem_t mod_trezorio_WebUSB_locals_dict_table[] = {
     {MP_ROM_QSTR(MP_QSTR_iface_num),
diff --git a/core/mocks/generated/trezorio/__init__.pyi b/core/mocks/generated/trezorio/__init__.pyi
index 8f34d9d1f01..c828c552de0 100644
--- a/core/mocks/generated/trezorio/__init__.pyi
+++ b/core/mocks/generated/trezorio/__init__.pyi
@@ -32,9 +32,9 @@ class HID:
         Sends message using USB HID (device) or UDP (emulator).
         """
 
-    def read(self, buf: bytes) -> int:
+    def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
         """
-        Reads message using USB HID (device) or UDP (emulator).
+        Reads message using HID (device) or UDP (emulator).
         """
 
     def write_blocking(self, msg: bytes, timeout_ms: int) -> int:
@@ -154,7 +154,7 @@ class WebUSB:
         Sends message using USB WebUSB (device) or UDP (emulator).
         """
 
-    def read(self, buf: bytes) -> int:
+    def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
         """
         Reads message using WebUSB (device) or UDP (emulator).
         """
diff --git a/core/src/apps/webauthn/fido2.py b/core/src/apps/webauthn/fido2.py
index 2125ec86997..5ee830ad7d4 100644
--- a/core/src/apps/webauthn/fido2.py
+++ b/core/src/apps/webauthn/fido2.py
@@ -378,7 +378,7 @@ async def _read_cmd(iface: HID) -> Cmd | None:
     # wait for incoming command indefinitely
     msg_len = await read
     buf = bytearray(msg_len)
-    read_len = iface.read(buf)
+    read_len = iface.read(buf, 0, msg_len)
     if read_len != msg_len:
         raise ValueError("Invalid length")
     while True:
@@ -421,7 +421,7 @@ async def _read_cmd(iface: HID) -> Cmd | None:
             try:
                 msg_len = await read
                 buf = bytearray(msg_len)
-                read_len = iface.read(buf)
+                read_len = iface.read(buf, 0, msg_len)
                 if read_len != msg_len:
                     raise ValueError("Invalid length")
             except loop.Timeout:
diff --git a/core/src/trezor/wire/codec/codec_v1.py b/core/src/trezor/wire/codec/codec_v1.py
index 68a2797ff56..7134222b7c5 100644
--- a/core/src/trezor/wire/codec/codec_v1.py
+++ b/core/src/trezor/wire/codec/codec_v1.py
@@ -27,8 +27,9 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
     # wait for initial report
     msg_len = await read
     report = bytearray(msg_len)
-    read_len = iface.read(report)
+    read_len = iface.read(report, 0, msg_len)
     if read_len != msg_len:
+        print("read_len", read_len, "msg_len", msg_len)
         raise CodecError("Invalid length")
     if report[0] != _REP_MARKER:
         raise CodecError("Invalid magic")
@@ -56,7 +57,7 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
         # wait for continuation report
         msg_len = await read
         report = bytearray(msg_len)
-        read_len = iface.read(report)
+        read_len = iface.read(report, 0, msg_len)
         if read_len != msg_len:
             raise CodecError("Invalid length")
         if report[0] != _REP_MARKER:

From 34559a47716ad0eb41603d66ac4ebe9ed1e6841c Mon Sep 17 00:00:00 2001
From: tychovrahe <brunam@seznam.cz>
Date: Wed, 4 Dec 2024 13:20:25 +0100
Subject: [PATCH 3/5] fixup! refactor(core): split polling can_read and reading
 from USB

---
 .../upymod/modtrezorio/modtrezorio-hid.h      | 16 +++++++++-------
 .../upymod/modtrezorio/modtrezorio-webusb.h   | 18 ++++++++++--------
 core/tests/test_trezor.wire.codec.codec_v1.py | 19 +++++++++++++++----
 3 files changed, 34 insertions(+), 19 deletions(-)

diff --git a/core/embed/upymod/modtrezorio/modtrezorio-hid.h b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
index 9b6e7c0a375..ee92df81c1d 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-hid.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
@@ -150,18 +150,20 @@ STATIC mp_obj_t mod_trezorio_HID_read(size_t n_args, const mp_obj_t *args) {
   mp_buffer_info_t buf = {0};
   mp_get_buffer_raise(args[1], &buf, MP_BUFFER_WRITE);
 
-  int offset = mp_obj_get_int(args[2]);
+  int offset = 0;
+  if (n_args >= 2) {
+    offset = mp_obj_get_int(args[2]);
+  }
 
-  int len = buf.len - offset;
+  int limit;
   if (n_args >= 3) {
-    int limit = mp_obj_get_int(args[3]);
-    if ((limit - offset) < len) {
-      len = (limit - offset);
-    }
+    limit = mp_obj_get_int(args[3]);
+  } else {
+    limit = buf.len - offset;
   }
 
   ssize_t r =
-      usb_hid_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], len);
+      usb_hid_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], limit);
   return MP_OBJ_NEW_SMALL_INT(r);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_HID_read_obj, 3, 4,
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
index bb3c639f14a..20b69c99f88 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
@@ -136,21 +136,23 @@ STATIC mp_obj_t mod_trezorio_WebUSB_read(size_t n_args, const mp_obj_t *args) {
   mp_buffer_info_t buf = {0};
   mp_get_buffer_raise(args[1], &buf, MP_BUFFER_WRITE);
 
-  int offset = mp_obj_get_int(args[2]);
+  int offset = 0;
+  if (n_args >= 2) {
+    offset = mp_obj_get_int(args[2]);
+  }
 
-  int len = buf.len - offset;
+  int limit;
   if (n_args >= 3) {
-    int limit = mp_obj_get_int(args[3]);
-    if ((limit - offset) < len) {
-      len = (limit - offset);
-    }
+    limit = mp_obj_get_int(args[3]);
+  } else {
+    limit = buf.len - offset;
   }
 
   ssize_t r =
-      usb_webusb_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], len);
+      usb_webusb_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], limit);
   return MP_OBJ_NEW_SMALL_INT(r);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_WebUSB_read_obj, 3, 4,
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_WebUSB_read_obj, 2, 4,
                                            mod_trezorio_WebUSB_read);
 
 STATIC const mp_rom_map_elem_t mod_trezorio_WebUSB_locals_dict_table[] = {
diff --git a/core/tests/test_trezor.wire.codec.codec_v1.py b/core/tests/test_trezor.wire.codec.codec_v1.py
index 5a73467e258..b4551077aa7 100644
--- a/core/tests/test_trezor.wire.codec.codec_v1.py
+++ b/core/tests/test_trezor.wire.codec.codec_v1.py
@@ -25,12 +25,23 @@ def mock_read(self, packet, gen):
         self.packet = packet
         return gen.send(len(packet))
 
-    def read(self, buffer):
+    def read(self, buffer, offset=0, limit=None):
         if self.packet is None:
             raise Exception("No packet to read")
-        buffer[:] = self.packet
-        self.packet = None
-        return len(buffer)
+        if limit is None:
+            limit = len(buffer) - offset
+
+        if len(self.packet) > limit:
+            end = offset + limit
+            buffer[offset:end] = self.packet[:limit]
+            self.packet = None
+            return limit
+        else:
+            end = offset + len(self.packet)
+            buffer[offset:end] = self.packet
+            read = len(self.packet)
+            self.packet = None
+            return read
 
     def wait_object(self, mode):
         return wait(mode | self.num)

From c9188fbcd96c366043c49462840762cd41226d93 Mon Sep 17 00:00:00 2001
From: tychovrahe <brunam@seznam.cz>
Date: Wed, 4 Dec 2024 14:26:29 +0100
Subject: [PATCH 4/5] fixup! refactor(core): split polling can_read and reading
 from USB

---
 core/embed/upymod/modtrezorio/modtrezorio-hid.h    | 2 +-
 core/embed/upymod/modtrezorio/modtrezorio-webusb.h | 2 +-
 core/mocks/generated/trezorio/__init__.pyi         | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/embed/upymod/modtrezorio/modtrezorio-hid.h b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
index ee92df81c1d..6f1c1bd2cd5 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-hid.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
@@ -143,7 +143,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_HID_write_obj,
 
 /// def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
 ///     """
-///     Reads message using HID (device) or UDP (emulator).
+///     Reads message using USB HID (device) or UDP (emulator).
 ///     """
 STATIC mp_obj_t mod_trezorio_HID_read(size_t n_args, const mp_obj_t *args) {
   mp_obj_HID_t *o = MP_OBJ_TO_PTR(args[0]);
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
index 20b69c99f88..a50e03dded0 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
@@ -129,7 +129,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_WebUSB_write_obj,
 
 /// def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
 ///     """
-///     Reads message using WebUSB (device) or UDP (emulator).
+///     Reads message using USB WebUSB (device) or UDP (emulator).
 ///     """
 STATIC mp_obj_t mod_trezorio_WebUSB_read(size_t n_args, const mp_obj_t *args) {
   mp_obj_WebUSB_t *o = MP_OBJ_TO_PTR(args[0]);
diff --git a/core/mocks/generated/trezorio/__init__.pyi b/core/mocks/generated/trezorio/__init__.pyi
index c828c552de0..463d7f12359 100644
--- a/core/mocks/generated/trezorio/__init__.pyi
+++ b/core/mocks/generated/trezorio/__init__.pyi
@@ -34,7 +34,7 @@ class HID:
 
     def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
         """
-        Reads message using HID (device) or UDP (emulator).
+        Reads message using USB HID (device) or UDP (emulator).
         """
 
     def write_blocking(self, msg: bytes, timeout_ms: int) -> int:
@@ -156,7 +156,7 @@ class WebUSB:
 
     def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
         """
-        Reads message using WebUSB (device) or UDP (emulator).
+        Reads message using USB WebUSB (device) or UDP (emulator).
         """
 from . import fatfs, haptic, sdcard
 POLL_READ: int  # wait until interface is readable and return read data

From 7d9a53c06946b51d4738f5e0c1b8d971f8807b8c Mon Sep 17 00:00:00 2001
From: tychovrahe <brunam@seznam.cz>
Date: Thu, 5 Dec 2024 14:08:07 +0100
Subject: [PATCH 5/5] fixup! refactor(core): split polling can_read and reading
 from USB

wip
---
 core/embed/io/usb/inc/io/usb.h                |  2 ++
 .../upymod/modtrezorio/modtrezorio-hid.h      | 24 +++++++++++------
 .../upymod/modtrezorio/modtrezorio-poll.h     |  9 +++----
 .../upymod/modtrezorio/modtrezorio-webusb.h   | 26 ++++++++++++-------
 core/mocks/generated/trezorio/__init__.pyi    |  4 +--
 core/src/apps/webauthn/fido2.py               |  8 ++----
 core/src/trezor/wire/codec/codec_v1.py        |  9 ++-----
 core/tests/test_trezor.wire.codec.codec_v1.py | 13 ++++------
 8 files changed, 49 insertions(+), 46 deletions(-)

diff --git a/core/embed/io/usb/inc/io/usb.h b/core/embed/io/usb/inc/io/usb.h
index a039719dc43..2646ce97b9c 100644
--- a/core/embed/io/usb/inc/io/usb.h
+++ b/core/embed/io/usb/inc/io/usb.h
@@ -26,6 +26,8 @@
 #include <io/usb_vcp.h>
 #include <io/usb_webusb.h>
 
+#define USB_PACKET_LEN 64
+
 // clang-format off
 //
 // USB stack high-level state machine
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-hid.h b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
index 6f1c1bd2cd5..928914b33cf 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-hid.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-hid.h
@@ -141,7 +141,7 @@ STATIC mp_obj_t mod_trezorio_HID_write(mp_obj_t self, mp_obj_t msg) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_HID_write_obj,
                                  mod_trezorio_HID_write);
 
-/// def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
+/// def read(self, buf: bytes, offset: int = 0) -> int
 ///     """
 ///     Reads message using USB HID (device) or UDP (emulator).
 ///     """
@@ -155,15 +155,23 @@ STATIC mp_obj_t mod_trezorio_HID_read(size_t n_args, const mp_obj_t *args) {
     offset = mp_obj_get_int(args[2]);
   }
 
-  int limit;
-  if (n_args >= 3) {
-    limit = mp_obj_get_int(args[3]);
-  } else {
-    limit = buf.len - offset;
+  if (offset < 0) {
+    mp_raise_ValueError("Negative offset not allowed");
+  }
+
+  uint32_t buffer_space = buf.len - offset;
+
+  if (buffer_space < USB_PACKET_LEN) {
+    mp_raise_ValueError("Buffer too small");
+  }
+
+  ssize_t r = usb_hid_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset],
+                           USB_PACKET_LEN);
+
+  if (r != USB_PACKET_LEN) {
+    mp_raise_msg(&mp_type_RuntimeError, "Unexpected read length");
   }
 
-  ssize_t r =
-      usb_hid_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], limit);
   return MP_OBJ_NEW_SMALL_INT(r);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_HID_read_obj, 3, 4,
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-poll.h b/core/embed/upymod/modtrezorio/modtrezorio-poll.h
index 3e0a738abdb..467429e3f25 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-poll.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-poll.h
@@ -169,15 +169,12 @@ STATIC mp_obj_t mod_trezorio_poll(mp_obj_t ifaces, mp_obj_t list_ref,
         if ((sectrue == usb_hid_can_read(iface)) ||
             (sectrue == usb_webusb_can_read(iface))) {
           ret->items[0] = MP_OBJ_NEW_SMALL_INT(i);
-          ret->items[1] = MP_OBJ_NEW_SMALL_INT(64);
+          ret->items[1] = MP_OBJ_NEW_SMALL_INT(USB_PACKET_LEN);
           return mp_const_true;
         }
       } else if (mode == POLL_WRITE) {
-        if (sectrue == usb_hid_can_write(iface)) {
-          ret->items[0] = MP_OBJ_NEW_SMALL_INT(i);
-          ret->items[1] = mp_const_none;
-          return mp_const_true;
-        } else if (sectrue == usb_webusb_can_write(iface)) {
+        if ((sectrue == usb_hid_can_write(iface)) ||
+            (sectrue == usb_webusb_can_write(iface))) {
           ret->items[0] = MP_OBJ_NEW_SMALL_INT(i);
           ret->items[1] = mp_const_none;
           return mp_const_true;
diff --git a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
index a50e03dded0..301d7b279e6 100644
--- a/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
+++ b/core/embed/upymod/modtrezorio/modtrezorio-webusb.h
@@ -127,7 +127,7 @@ STATIC mp_obj_t mod_trezorio_WebUSB_write(mp_obj_t self, mp_obj_t msg) {
 STATIC MP_DEFINE_CONST_FUN_OBJ_2(mod_trezorio_WebUSB_write_obj,
                                  mod_trezorio_WebUSB_write);
 
-/// def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
+/// def read(self, buf: bytes, offset: int = 0) -> int
 ///     """
 ///     Reads message using USB WebUSB (device) or UDP (emulator).
 ///     """
@@ -141,18 +141,26 @@ STATIC mp_obj_t mod_trezorio_WebUSB_read(size_t n_args, const mp_obj_t *args) {
     offset = mp_obj_get_int(args[2]);
   }
 
-  int limit;
-  if (n_args >= 3) {
-    limit = mp_obj_get_int(args[3]);
-  } else {
-    limit = buf.len - offset;
+  if (offset < 0) {
+    mp_raise_ValueError("Negative offset not allowed");
+  }
+
+  uint32_t buffer_space = buf.len - offset;
+
+  if (buffer_space < USB_PACKET_LEN) {
+    mp_raise_ValueError("Buffer too small");
+  }
+
+  ssize_t r = usb_webusb_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset],
+                              USB_PACKET_LEN);
+
+  if (r != USB_PACKET_LEN) {
+    mp_raise_msg(&mp_type_RuntimeError, "Unexpected read length");
   }
 
-  ssize_t r =
-      usb_webusb_read(o->info.iface_num, &((uint8_t *)buf.buf)[offset], limit);
   return MP_OBJ_NEW_SMALL_INT(r);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_WebUSB_read_obj, 2, 4,
+STATIC MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mod_trezorio_WebUSB_read_obj, 2, 3,
                                            mod_trezorio_WebUSB_read);
 
 STATIC const mp_rom_map_elem_t mod_trezorio_WebUSB_locals_dict_table[] = {
diff --git a/core/mocks/generated/trezorio/__init__.pyi b/core/mocks/generated/trezorio/__init__.pyi
index 463d7f12359..4d8d3cda797 100644
--- a/core/mocks/generated/trezorio/__init__.pyi
+++ b/core/mocks/generated/trezorio/__init__.pyi
@@ -32,7 +32,7 @@ class HID:
         Sends message using USB HID (device) or UDP (emulator).
         """
 
-    def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
+    def read(self, buf: bytes, offset: int = 0) -> int
         """
         Reads message using USB HID (device) or UDP (emulator).
         """
@@ -154,7 +154,7 @@ class WebUSB:
         Sends message using USB WebUSB (device) or UDP (emulator).
         """
 
-    def read(self, buf: bytes, offset: int = 0, limit: int | None = None) -> int
+    def read(self, buf: bytes, offset: int = 0) -> int
         """
         Reads message using USB WebUSB (device) or UDP (emulator).
         """
diff --git a/core/src/apps/webauthn/fido2.py b/core/src/apps/webauthn/fido2.py
index 5ee830ad7d4..b55f56281cb 100644
--- a/core/src/apps/webauthn/fido2.py
+++ b/core/src/apps/webauthn/fido2.py
@@ -378,9 +378,7 @@ async def _read_cmd(iface: HID) -> Cmd | None:
     # wait for incoming command indefinitely
     msg_len = await read
     buf = bytearray(msg_len)
-    read_len = iface.read(buf, 0, msg_len)
-    if read_len != msg_len:
-        raise ValueError("Invalid length")
+    iface.read(buf, 0)
     while True:
         ifrm = overlay_struct(bytearray(buf), desc_init)
         bcnt = ifrm.bcnt
@@ -421,9 +419,7 @@ async def _read_cmd(iface: HID) -> Cmd | None:
             try:
                 msg_len = await read
                 buf = bytearray(msg_len)
-                read_len = iface.read(buf, 0, msg_len)
-                if read_len != msg_len:
-                    raise ValueError("Invalid length")
+                iface.read(buf, 0)
             except loop.Timeout:
                 if __debug__:
                     warning(__name__, "_ERR_MSG_TIMEOUT")
diff --git a/core/src/trezor/wire/codec/codec_v1.py b/core/src/trezor/wire/codec/codec_v1.py
index 7134222b7c5..e39606be686 100644
--- a/core/src/trezor/wire/codec/codec_v1.py
+++ b/core/src/trezor/wire/codec/codec_v1.py
@@ -27,10 +27,7 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
     # wait for initial report
     msg_len = await read
     report = bytearray(msg_len)
-    read_len = iface.read(report, 0, msg_len)
-    if read_len != msg_len:
-        print("read_len", read_len, "msg_len", msg_len)
-        raise CodecError("Invalid length")
+    iface.read(report, 0)
     if report[0] != _REP_MARKER:
         raise CodecError("Invalid magic")
     _, magic1, magic2, mtype, msize = ustruct.unpack(_REP_INIT, report)
@@ -57,9 +54,7 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
         # wait for continuation report
         msg_len = await read
         report = bytearray(msg_len)
-        read_len = iface.read(report, 0, msg_len)
-        if read_len != msg_len:
-            raise CodecError("Invalid length")
+        iface.read(report, 0)
         if report[0] != _REP_MARKER:
             raise CodecError("Invalid magic")
 
diff --git a/core/tests/test_trezor.wire.codec.codec_v1.py b/core/tests/test_trezor.wire.codec.codec_v1.py
index b4551077aa7..8fcf0add3c7 100644
--- a/core/tests/test_trezor.wire.codec.codec_v1.py
+++ b/core/tests/test_trezor.wire.codec.codec_v1.py
@@ -25,17 +25,14 @@ def mock_read(self, packet, gen):
         self.packet = packet
         return gen.send(len(packet))
 
-    def read(self, buffer, offset=0, limit=None):
+    def read(self, buffer, offset=0):
         if self.packet is None:
             raise Exception("No packet to read")
-        if limit is None:
-            limit = len(buffer) - offset
 
-        if len(self.packet) > limit:
-            end = offset + limit
-            buffer[offset:end] = self.packet[:limit]
-            self.packet = None
-            return limit
+        buffer_space = len(buffer) - offset
+
+        if len(self.packet) > buffer_space:
+            raise Exception("Buffer too small")
         else:
             end = offset + len(self.packet)
             buffer[offset:end] = self.packet