diff --git a/doc/system_description/software.md b/doc/system_description/software.md index dc8910a..0df18fb 100644 --- a/doc/system_description/software.md +++ b/doc/system_description/software.md @@ -1,21 +1,22 @@ - -# NOTE: this document is outdated, an update is pending. - -# MTA1-MKDF software +# Tillitis Key software ## Definitions - * Firmware -- software that is part of ROM, and is supplied via the - FPGA bit stream - * Secure Application (short: Application) -- software supplied by - the host machine, which is received, measured, and loaded by the - firmware. -## Types -The PicoRV32 is a 32-bit RISC-V system. All types are little-endian. + * Firmware -- software that is part of ROM, and is currently + supplied via the FPGA bit stream. + * Application -- software supplied by the host machine, which is + received, loaded, and measured by the firmware. + +## CPU + +We use a PicoRV32, a 32-bit RISC-V system, as the CPU for running the +firmware and the loaded app. All types are little-endian. ## Constraints + The application FPGA is a Lattice UP5K, with the following specifications: + * 32KB x 4 SPRAM => 128KB for Application * 4Kb x 30 EBR => 120Kb, PicoRV32 uses ~4 EBR internally => 13KB for Firmware. We should probably aim for less; 8KB should be the @@ -23,19 +24,21 @@ specifications: ## Introduction -The MTA1_MKDF has two modes of operation; firmware/loader mode and -application mode. The firmware mode has the responsibility of receive, -measure, and load the application. +The Tillitis Key has two modes of operation; firmware/loader mode and +application mode. The firmware mode has the responsibility of +receiving, measuring, and loading the application. The firmware and application uses a memory mapped IO for SoC -communication. The memory map resides at `0x9000_0000`. The -application has a constrained variant of the firmware memory map, -which is outlined below. E.g. UID and UDA are not readable, and the -`APP_{ADDR, SIZE}` are not writable for the application. +communication. This MMIO resides at `0xc000_0000`. *Nota bene*: All +access to MMIO should be word (32 bit) aligned. -The MTA1_MKDF software communicates to the host via the `{RX,TX}_FIFO` -registers, using the framing protocol described in [Framing -Protocol](../framing_protocol/framing_protocol.md). +The application has a constrained variant of the firmware memory map, +which is outlined below. E.g. UDS isn't readable, and the `APP_{ADDR, +SIZE}` are not writable for the application. + +The software on the Tillitis Key communicates to the host via the +`{RX,TX}_FIFO` registers, using the framing protocol described in +[Framing Protocol](../framing_protocol/framing_protocol.md). The firmware defines a protocol (command/response interface) on top of the framing layer, which is used to bootstrap the application onto the @@ -50,24 +53,27 @@ between the host and the device. ## Firmware -The firware is part of FPGA bitstream (ROM), and is loaded at -`0x0000_1000`. +The firmware is part of FPGA bitstream (ROM), and is loaded at +`0x0000_0000`. ### Reset -The PicoRV32 executes `_start` from `crt0.S` `.text` at `0x0000_1000`, -which initializes the stack, `.data`, and `.bss` at -`0x8000_0000`. When the initialization is finished, the firmware waits -for incoming commands from the host, by busy-polling the -`RX_FIFO_{AVAILABLE,DATA}`registers. When a complete command is read, -the firmware executes the command. +The PicoRV32 starts executing at `0x0000_0000`. Our firmware starts at +`_start` from `start.S` which initializes the `.data`, and `.bss` at +`0x4000_0000` and upwards. A stack is also initialized, starting at +0x4000_fff0 and downwards. When the initialization is finished, the +firmware waits for incoming commands from the host, by busy-polling +the `RX_FIFO_{AVAILABLE,DATA}`registers. When a complete command is +read, the firmware executes the command. ### Loading an application -The purpose of the firmware is to bootstrapping an application. - 1. The host sends a raw binary, targeted to be loaded at - `0x8000_0000` in the device. The host starts off by sending the - binary size using the `FW_CMD_LOAD_APP_SIZE` command. +The purpose of the firmware is to bootstrap an application. The host +will send a raw binary targeted to be loaded at `0x4001_0000` in the +device. + + 1. The host sends sets the size of the app by using the + `FW_CMD_LOAD_APP_SIZE` command. 2. The firmware executes `FW_CMD_LOAD_APP_SIZE` command, which stores the application size into `APP_SIZE`, and sets `APP_ADDR` to zero. A `FW_RSP_LOAD_APP_SIZE` reponse is sent back to the @@ -75,16 +81,19 @@ The purpose of the firmware is to bootstrapping an application. 3. If the the host receive a sucessful command, it will send multiple `FW_CMD_LOAD_APP_DATA` commands, containing the full application. - 4. For each received `FW_CMD_LOAD_APP_DATA` commands, the firmware - measures (XXX define how blake2s is used) the data, and places it - into `0x8000_0000`. The firmware response with - `FW_RSP_LOAD_APP_DATA` response to the host for each received - block. - 5. When the final block of the application image is received, - `0x8000_0000` is written to `APP_ADDR`. The `CDI` is computed by - used the `UDS` and measurement from the application, and placed - in the `CDI` register. The final `FW_RSP_LOAD_APP_DATA` response - is sent to the host, completing the loading. + 4. For each received `FW_CMD_LOAD_APP_DATA` command the firmware + places the data into `0x4001_0000` and upwards. The firmware + response with `FW_RSP_LOAD_APP_DATA` response to the host for + each received block. + 5. When the final block of the application image is received, we + measure the application by computing a BLAKE2s digest over the + entire application, + + The Compound Device Identifier is computed by using the `UDS` and + the measurement of the application, and placed in the `CDI` + register. Then `0x4001_0000` is written to `APP_ADDR`. The final + `FW_RSP_LOAD_APP_DATA` response is sent to the host, completing + the loading. NOTE: The firmware uses SPRAM for data and stack. We need to make sure that the application image does not overwrite the firmware's running @@ -97,31 +106,31 @@ application. ### Starting an application Starting an application includes the "switch to application mode" -step, which is done by writing to the `SWITCH_APP` regiester. The +step, which is done by writing to the `SWITCH_APP` register. The switch from firmware mode to application mode is a mode switch, and -context switch. Enter application mode, means the the MMIO region is -restricted; E.g. some registers are removed (`UDS`), and some are +context switch. When entering application mode the MMIO region is +restricted; e.g. some registers are removed (`UDS`), and some are switched from read/write to read-only. This is outlined in the memory map below. There is no other means of getting back from application mode to -firmware mode, than resetting/power cycling the device. +firmware mode than resetting/power cycling the device. Prerequisites: `APP_SIZE` and `APP_ADDR` has to be non-zero. +Procedure: + 1. The host sends `FW_CMD_RUN_APP` to the device. - 2. The firmware respons with `FW_RSP_RUN_APP` + 2. The firmware responds with `FW_RSP_RUN_APP` 3. The firmware writes a non-zero to `SWITCH_APP`, and executes - ``` - // a0 = 0x9000_0000 + 0x420 (APP_ADDR address) - lw a0,1056(a0) - jalr x0,0(a0) - ``` - 4. The device is now in application mode, and executes the code from - `0x8000_0000`. + assembler code that writes zeros to stack and data of the + firmware, then jumps to what's in APP_ADDR. + 4. The device is now in application mode and is executing the + application. ### Protocol definition Available commands/reponses: + #### `FW_{CMD,RSP}_LOAD_APP_SIZE` #### `FW_{CMD,RSP}_LOAD_APP_DATA` #### `FW_{CMD,RSP}_RUN_APP` @@ -129,20 +138,19 @@ Available commands/reponses: #### `FW_{CMD,RSP}_UID` #### `FW_{CMD,RSP}_TRNG_DATA` #### `FW_{CMD,RSP}_TRNG_STATUS` + #### `FW_{CMD,RSP}_VERIFY_DEVICE` + Verification that the device is an authentic Mullvad device. Implemented using challenge/response. #### `FW_{CMD,RSP}_GET_APPLICATION_DIGEST` + This command returns the un-keyed hash digest for the application that was loaded. It allows the host to verify that the application was correctly loaded. This means that the CDI calculated will be correct given that the UDS has not been modified. -XXX Should we think a bit more about versioning/possiblity to extend? -Is 1B enough for a command/response range? - - #### Get the name and version of the device ``` @@ -166,11 +174,12 @@ host <- ``` #### Load an application + ``` host -> u8 CMD[1 + 32]; - CMD[0].len = 5 // command frame format + CMD[0].len = 4 // command frame format CMD[1] = 0x03 // FW_CMD_LOAD_APP_SIZE CMD[2..6] = APP_SIZE @@ -187,20 +196,19 @@ host <- RSP[3..] = 0 - -repeat ceil(APP_SIZE / 63) times: +repeat ceil(APP_SIZE / 127) times: host -> - u8 CMD[1 + 64]; + u8 CMD[1 + 128]; - CMD[0].len = 65 // command frame format + CMD[0].len = 128 // command frame format CMD[1] = 0x05 // FW_CMD_LOAD_APP_DATA - CMD[2..] = APP_DATA (pad with zeros) + CMD[2..] = APP_DATA (127 bytes of app data, pad with zeros) host <- u8 RSP[1 + 4] - RSP[0].len = 5 // command frame format + RSP[0].len = 4 // command frame format RSP[1] = 0x06 // FW_RSP_LOAD_APP_DATA RSP[2] = STATUS @@ -210,37 +218,106 @@ host <- ### Memory map -The memory map exposes SoC functionality to the software, when in -firmware mode (privileged mode) It is s set of memory mapped -registers, starting at base address `0x9000_0000`. +Assigned top level prefixes: -| *name* | *r/w* | *offset* | *size* | *type* | *content* | *description* | -|--------------------|-------|----------|--------|---------|-----------|---------------------------------------------------------| -| UDS[^1] | r | 0x0 | 32B | u8[32] | | Unique Device Secret key. | -| UDA | r | 0x20 | 16B | u8[16] | | Unique Device Authentication key. | -| SWITCH_APP | w | 0x30 | 1B | u8 | | Switch to application mode. Write non-zero to trigger. | -| XXX 460 bytes hole | | | | | | | -| UDI | r | 0x200 | 8B | u64 | | Unique Device ID (UDI). | -| NAME0 | r | 0x208 | 4B | char[4] | "mta1" | | -| NAME1 | r | 0x20c | 4B | char[4] | "mkdf" | | -| VERSION | r | 0x210 | 4B | u32 | 1 | Current version. | -| RX_FIFO_AVAILABLE | r | 0x214 | 1B | u8 | | Non-zero if a valid byte can be read from RX_FIFO_DATA. | -| RX_FIFO_DATA | r | 0x215 | 1B | u8 | | FIFO Rx data. | -| TX_FIFO_AVAILABLE | r | 0x216 | 1B | u8 | | Non-zero if a valid byte can be written to TX_FIFO_DATA | -| TX_FIFO_DATA | w | 0x217 | 1B | u8 | | FIFO Tx data. | -| LED | r/w | 0x218 | 4B | u32 | | LED | -| COUNTER | r | 0x21c | 4B | u32 | | Counter | -| TRNG_STATUS | r | 0x220 | 4B | u32 | | data_ready/error | -| TRNG_DATA | r | 0x224 | 4B | u32 | | TRNG data | -| XXX 472 bytes hole | | | | | | | -| CDI | r/w | 0x400 | 32B | u8[32] | | Compound Device Identifier (CDI). UDS+measurement... | -| APP_ADDR | r/w | 0x420 | 4B | u32 | | Application address (0x8000_0000) | -| APP_SIZE | r/w | 0x424 | 4B | u32 | | Application size | +| *name* | *prefix* | *address length* | +|----------|----------|--------------------------------------| +| ROM | 0b00 | 30 bit address | +| RAM | 0b01 | 30 bit address | +| reserved | 0b10 | | +| MMIO | 0b11 | 6 bits for core select, 24 bits rest | + +Addressing: + +``` +31st bit 0th bit +v v +0000 0000 0000 0000 0000 0000 0000 0000 + +- Bits [31 .. 30] (2 bits): Top level prefix (described above) +- Bits [29 .. 24] (6 bits): Core select. We want to support at least 16 cores +- Bits [23 .. 0] (24 bits): Memory/in-core address. +``` + +The memory exposes SoC functionality to the software when in firmware +mode. It is a set of memory mapped registers (MMIO), starting at base +address `0xc000_0000`. For specific offsets/bitmasks, see the file +[mta1_mkdf_mem.h](../../hw/application_fpga/fw/mta1_mkdf_mem.h) (in +this repo). + +Assigned core prefixes: + +| *name* | *prefix* | +|--------|----------| +| ROM | 0x00 | +| RAM | 0x40 | +| TRNG | 0xc0 | +| TIMER | 0xc1 | +| UDS | 0xc2 | +| UART | 0xc3 | +| TOUCH | 0xc4 | +| MTA1 | 0xff | +| | | + +Every core has a NAME1, NAME2, and VERSION to identify it. + +Examples: + +| *address* | *description* | +|------------|-----------------| +| 0xc3000004 | NAME1 in UART | +| 0xff000000 | NAME0 in MTA1 | +| 0xff000008 | VERSION in MTA1 | + +*Nota bene*: All MMIO accesses should be 32 bit wide, e.g use `lw` and `sw`. + +| *name* | *fw* | *app | *size* | *type* | *content* | *description* | +|--------------------|------|------------|--------|---------|-----------|--------------------------------------------------------| +| `TRNG_NAME0` | r | r | 4B | char[4] | | ID of core | +| `TRNG_NAME1` | r | r | 4B | char[4] | | ID of core | +| `TRNG_VERSION` | r | r | 4B | u32 | | Version of core | +| `TRNG_STATUS` | r | r | | | | TBD | +| `TRNG_SAMPLE_RATE` | | r | | | | TBD | +| `TRNG_ENTROPY` | | | | | | TBD | +| `TIMER_NAME0` | r | r | | | | ID of core | +| `TIMER_NAME1` | r | r | | | | ID of core | +| `TIMER_VERSION` | r | r | | | | Version of core | +| `TIMER_CTRL` | | | | | | TBD | +| `TIMER_STATUS` | r | | | | | TBD | +| `TIMER_PRESCALER` | | r/w | | | | TBD | +| `TIMER_TIMER` | | r | | | | TBD | +| `UDS_NAME0` | r | invisible | | | | ID of core | +| `UDS_NAME1` | r | invisible | | | | ID of core | +| `UDS_VERSION` | r | invisible | | | | Version of core | +| `UDS_START` | r[^1]| invisible | 4B | u8[32] | | First word of Unique Device Secret key. | +| `UDS_LAST` | | invisible | | | | The last word of the UDS | +| `UART_NAME0` | r | r | | | | ID of core | +| `UART_NAME1` | r | r | | | | ID of core | +| `UART_VERSION` | r | r | | | | Version of core | +| `UART_BITRATE` | r/w | | | | | TBD | +| `UART_DATABITS` | r/w | | | | | TBD | +| `UART_STOPBITS` | r/w | | | | | TBD | +| `UART_RX_STATUS` | r | r | 1B | u8 | | Non-zero when there is data to read | +| `UART_RX_DATA` | r | r | 1B | u8 | | Data to read. Only LSB contains data | +| `UART_TX_STATUS` | r | r | 1B | u8 | | Non-zero when it's OK to write data | +| `UART_TX_DATA` | w | w | 1B | u8 | | Data to send. Only LSB contains data | +| `TOUCH_NAME0` | r | r | | | | ID of core | +| `TOUCH_NAME1` | r | r | | | | ID of core | +| `TOUCH_VERSION` | r | r | | | | Version of core | +| `TOUCH_STATUS` | r/w | r/w | | | | STATUS_EVENT_BIT set 1 when touched; write to it after | +| `UDA` | r | | 16B | u8[16] | | Unique Device Authentication key. | +| `UDI` | r | | 8B | u64 | | Unique Device ID (UDI). | +| `QEMU_DEBUG` | w | w | | u8 | | Debug console (only in QEMU) | +| `NAME0` | r | r | 4B | char[4] | "mta1" | ID of core/stick | +| `NAME1` | r | r | 4B | char[4] | "mkdf" | ID of core/stick | +| `VERSION` | r | r | 4B | u32 | 1 | Current version. | +| `SWITCH_APP` | w | invisible? | 1B | u8 | | Switch to application mode. Write non-zero to trigger. | +| `LED` | w | w | 1B | u8 | | | +| `GPIO` | | | | | | | +| `APP_ADDR` | r/w | r | 4B | u32 | | Application address (0x4000_0000) | +| `APP_SIZE` | r/w | r | 4B | u32 | | Application size | +| `DEBUG` | | | | | | TBD | +| `CDI_START` | r/w | r | 32B | u8[32] | | Compound Device Identifier (CDI). UDS+measurement... | +| `CDI_LAST` | | r | | | | Last word of CDI | [^1]: The UDS can only be read *once* per power-cycle. - -## Application - -### Memory map -See the [Memory model](./memory_model.md) for information about the -memory map and how access to memory areas work.