Cmep
The F00D processor performs most of the PSVita cryptography tasks including storing and handing of the most secure keys. There is little information about it though. It was named after the e_machine
field of the ELF headers, but its official name is CMeP (Control MeP). CMEP is a Toshiba MeP-c5 core.
More information can be found in Toshiba documentations. For example: https://toshiba.semicon-storage.com/info/docget.jsp?did=14997&prodName=TMPV7504XBG.
You can find an open source F00D<->ARM TZ protocol implementation at https://github.com/xyzz/f00d.
Communication
Communication seems to go through some sort of FIFO register.
Write
To write, put the double word into 0xE0000010
. Next read 0xE0000010
until it returns 0, which indicates the data was read by the F00D processor.
Read
To read, get a double word from 0xE0000000
. If it returns 0, no data is available. Otherwise, acknowledge that the data has been read by putting the same data into 0xE0000000
.
Extra ports
In addition to the 0xE0000000
and 0xE0000010
, the communication with F00D seems to happen with other ports too.
Port | Read | Write | Used by |
---|---|---|---|
0xE0000004 | YES | ? | SMC 0x12d, 0x136, 0x137, 0x13B Interrupt 0xC8 |
0xE0000008 | YES | ? | SMC 0x12d, 0x136, 0x137, 0x13B Interrupt 0xC8 |
0xE000000C | YES | ? | SMC 0x12d, 0x136, 0x137, 0x13B Interrupt 0xC8 |
0xE0000014 | YES | YES | Used to send commands to f00d secure module, see Executing sm commands |
0xE0000018 | YES | YES | Used to send commands to f00d secure module, see Executing sm commands |
0xE000001C | YES | YES | Used to send commands to f00d secure module, see Executing sm commands |
0xE0000054 | ? | YES | SMC 0x12d, 0x135, 0x13B, Interrupt 0xC8 |
0xE0000058 | ? | YES | SMC 0x12d, 0x135, 0x13B, Interrupt 0xC8 |
0xE000005C | ? | YES | SMC 0x12d, 0x135, 0x13B, Interrupt 0xC8 |
0xE0010000 | YES | YES | Used by F00D Command 0 to prepare F00D to receive an address that contains the secure_kernel.enp. |
0xE0010004 | YES | ? | Used by F00D Command 0 to check if the value written in 0xE0010000 is okay (it should return a value <= 0).
|
Protocol
A 32-bit command buffer is defined below. The command is sent to the F00D processor with the method listed above.
Bit End | Bit Start | Name | Description |
---|---|---|---|
31 | 16 | Size | Size of the command buffer |
18 | 13 | - | Always 0 |
12 | 8 | ID | Command ID |
7 | 1 | - | Always 0 |
0 | 0 | Valid | Set to 1 |
Command ID
There are a total of 14 commands. Below are notes on different commands. Commands pass data through the 0x100 shared buffer (set up in command 0).
0x0
This command is used to setup a shared buffer with F00D. First F00D will write in 0xE0000000
either 0x200 or 0x600 (and if an error happened, 0x400 ?). If the value 0x600 is written, it will first setup a buffer that contains the F00D secure_kernel.enp. First it will write 0x1 to 0xE0010000
and after that 0x0 to 0xE0010000
, next, it will wait 0xE0010000
return 0 and 0xE0010004
return a value <= 0x0. If everything goes alright, it will clear the low 2 bits of the F00D secure_kernel.enp address (normally at 0x1F850000) and OR it with 0x1 and then write it to 0xE0000010
. After it, the process is the same that the 0x200. If the value 0x200 is written, it will set the 0x100 sized shared buffer. First the physical address of the buffer is written to 0xE0000010
and then command 0x0 is written.
0x1
This command is called by a subroutine of SceSblSmsched#sceSblSmSchedStopForTZS or SceSblSmsched module_start (if an error happened while SceSblSmsched was initializing). This command seems to be used to ask F00D to remove all resource allocated (like shared memory address, secure module loaded, etc), and probably power off or reset it.
0x2
Load a sm.
Offset | Size | Description |
---|---|---|
0x0 | 0x4 | num_paddrs |
0x4 | 0x4 | paddr_list for sm elf |
0x8 | 0x4 | buf_0x40: some 0x40 buffer |
0xC | 0x4 | ctx_0x4 |
0x10 | 0x4 | ctx_0x8 |
0x14 | 0x4 | ctx_0xC |
0x1C | 0x4 | field_60: system version (2) |
0x20 | 0x4 | partition ID |
0x3
Load previously suspended sm.
Offset | Size | Description |
---|---|---|
0x0 | 0x4 | num_paddrs |
0x4 | 0x4 | paddr_list for suspend buffer |
0x8 | 0x4 | buf_0x40: some 0x40 buffer |
0xC | 0x4 | delayed_cmd |
0x4
Suspend current sm.
Offset | Size | Description |
---|---|---|
0x0 | 0x4 | num_paddrs |
0x4 | 0x4 | paddr_list for suspend buffer |
0x8 | 0x4 | buf_0x40: some 0x40 buffer |
0xC | 0x4 | delayed_cmd |
0x5
Kill current sm.
0x6
Force stop? Called from sceSblSmSchedDeleteAll.
0x7
Unused.
0x8
Unused.
0x9
Set a 0x80 sized shared buffer.
Offset | Size | Description |
---|---|---|
0x0 | 0x4 | paddr |
0x4 | 0x4 | length |
0xA
Set the encrypted signed revoke list.
Offset | Size | Description |
---|---|---|
0x0 | 0x4 | num_paddrs |
0x4 | 0x4 | paddr_list for signed revoke list |
0xB
0xC
0xD
0xE
0xF
0x10
Interrupts
There are 4 interrupts that F00D sends. There are only two interrupt handles, however.
cry2arm0
: handles interrupt 200. This is notifications about current sm status changes (loaded, unloaded, suspended, etc)cry2arm123
: handles interrupts 201, 202, 203. This interrupt is sent once an sm command has finished processing (see below).
Executing sm commands
When a SM is loaded, you can execute a command it provides by writing into registers 0xE0000014, 0xE0000018, 0xE000001C paddr to the command buffer OR'd with 1.
Command buffer structure (as seen on FWs 3.60-3.73):
Offset | Size | Description |
---|---|---|
0x0 | 0x4 | Size of header + data |
0x4 | 0x4 | Command ID |
0x8 | 0x4 | Command return value is written here by the SM |
0xC | 0x4 | unk2 |
0x10 | 0x30 | padding |
0x40 | variable, chosen by NS Kernel, max=0x1000-0x40 | data buffer |
On FW 0.931, and maybe in later prototype FWs, the data buffer is located at offset 0x10 instead of 0x40. Thus we can ask why they added the 0x30 bytes padding.
Once result is available, ARM will get an interrupt 201-203. Read status code from 0xE0000004 (or 0xE0000008, 0xE000000C) and confirm you received it by writing it back to the same register.
Possible results:
- 1: command executed successfully
- 3: invalid command ID
- 5: invalid command buffer paddr (e.g. trying to pass secure memory)
- 9: SCE_SBL_ERROR_COMMON_EIO
Memory
F00D has its own private 128KB memory from 0x00800000
to 0x00820000
. Secure Modules are typically loaded to 0x0080B000
. secure_kernel is loaded to 0x00800000
.
Task states
ARM Trust Zone implements a scheduler for sm tasks. Normally, only one task can run on F00D at a time. The external scheduler running on ARM allows to have multiple tasks at once. The following provides an explanation of various states the task can be in.
ID | Description |
---|---|
1 | Created / Suspended (Unloaded) |
2 | Running |
3 | Errored (Unloaded) |
4 | ? (Unloaded) |
5 | ? (Unloaded) |
6 | Start/resume requested |
7 | Suspending |
8 | ? |
9 | ? |
10 | ? |
11 | Suspend requested |
12 | ? |