TSEC

Like most Tegra based devices, the Switch's GPU also includes a Falcon microprocessor.

Driver

A host driver for communicating with the Falcon is mapped to physical address 0x54500000 with a total size of 0x40000 bytes and exposes several registers.

Registers

Name	Address	Width
FALCON_IRQMSET	0x54501010	0x04
FALCON_IRQDEST	0x5450101C	0x04
FALCON_SCRATCH0	0x54501040	0x04
FALCON_SCRATCH1	0x54501044	0x04
FALCON_ITFEN	0x54501048	0x04
FALCON_CPUCTL	0x54501100	0x04
FALCON_BOOTVEC	0x54501104	0x04
FALCON_DMACTL	0x5450110C	0x04
FALCON_DMATRFBASE	0x54501110	0x04
FALCON_DMATRFMOFFS	0x54501114	0x04
FALCON_DMATRFCMD	0x54501118	0x04
FALCON_DMATRFFBOFFS	0x5450111C	0x04

FALCON_IRQMSET

Used for configuring Falcon's IRQs.

FALCON_IRQDEST

Used for configuring Falcon's IRQs.

FALCON_SCRATCH0

MMIO register for reading/writing data to Falcon.

FALCON_SCRATCH1

MMIO register for reading/writing data to Falcon.

FALCON_ITFEN

Bits	Description
0	FALCON_ITFEN_CTXEN
1	FALCON_ITFEN_MTHDEN

Used for enabling/disabling Falcon interfaces.

FALCON_CPUCTL

Bits	Description
0	FALCON_CPUCTL_STARTCPU

Used for signaling Falcon's CPU.

FALCON_BOOTVEC

Takes the Falcon's boot vector address.

FALCON_DMACTL

Bits	Description
1	FALCON_DMACTL_DMEM_SCRUBBING
2	FALCON_DMACTL_IMEM_SCRUBBING

Used for configuring the Falcon's DMA engine.

FALCON_DMATRFBASE

Takes the host's base address for transferring data to/from the Falcon (DMA).

FALCON_DMATRFMOFFS

Takes the offset for the host's source memory being transferred.

FALCON_DMATRFCMD

Bits	Description
1	FALCON_DMATRFCMD_IDLE (this is set if the engine is idle)
4	FALCON_DMATRFCMD_IMEM
9-10	FALCON_DMATRFCMD_SIZE_256B

Used for configuring DMA transfers.

FALCON_DMATRFFBOFFS

Takes the offset for Falcon's target memory being transferred.

Boot Process

The Falcon is configured and initialized by the first bootloader during key generation (sub_400114FC).

Initialization

During this stage several clocks are programmed.

// Program the HOST1X clock and resets
set_host1x_clkrst();

// Program the TSEC clock and resets
set_tsec_clkrst();

// Program the QSPI clock and resets (no source)
set_qspi_clkrst();

// Program the SOR1 clock and resets (no source)
set_sor1_clkrst0();

// Program the SOR1 clock and resets
set_sor1_clkrst1();

// Enable clock and resets for H group
set_h_clkrst();

Configuration

In this stage the Falcon IRQs, interfaces and DMA engine are configured.

// Clear the Falcon DMA control register
*(u32 *)FALCON_DMACTL = 0;

// Enable Falcon IRQs
*(u32 *)FALCON_IRQMSET = 0xFFF2;

// Enable Falcon IRQs
*(u32 *)FALCON_IRQDEST = 0xFFF0;

// Enable Falcon interfaces
*(u32 *)FALCON_ITFEN = 0x03;

// Wait for Falcon's DMA engine to be idle
wait_flcn_dma_idle();

Firmware loading

The Falcon firmware code is stored in the first bootloader's data segment in IMEM.

// Set DMA transfer base address to 0x40011900 >> 0x08
*(u32 *)FALCON_DMATRFBASE = 0x400119;

u32 trf_mode = 0;     // A value of 0 sets FALCON_DMATRFCMD_IMEM
u32 dst_offset = 0;
u32 src_offset = 0;

// Load code into Falcon (0x100 bytes at a time)
while (src_offset < 0xF00)
{
   flcn_load_firm(trf_mode, src_offset, dst_offset);
   src_offset += 0x100;
   dst_offset += 0x100;
}

Firmware booting

Falcon is booted up and the first bootloader waits for it to finish.

// Set host1x sync config
*(u32 *)0x50003300 = 0x34C2E1DA;

// Clear Falcon scratch1 MMIO
*(u32 *)FALCON_SCRATCH1 = 0;

// Set Falcon boot key version in scratch0 MMIO
*(u32 *)FALCON_SCRATCH0 = 0x01;

// Set Falcon's boot vector address
*(u32 *)FALCON_BOOTVEC = 0;

// Signal Falcon's CPU
*(u32 *)FALCON_CPUCTL = 0x02;

// Wait for Falcon's DMA engine to be idle
wait_flcn_dma_idle();

u32 boot_res = 0;
u32 time = 0;

while (!boot_res)
{
   // Read boot result from scratch1 MMIO
   boot_res = *(u32 *)FALCON_SCRATCH1;
   
   // Read from RTC_MILLISECONDS
   time = rtc_read();
   
   // Booting is taking too long
   if (time > 2000000)
      panic();
}

// Invalid boot result was returned
if (boot_res != 0xB0B0B0B0)
   panic();

Keygen

In this final stage the Falcon device key is generated by reading SOR registers modified by Falcon.

// Clear host1x sync config
*(u32 *)0x50003300 = 0;

// Generate Falcon device key
u32 falcon_device_key[4]; 
falcon_device_key[0] = *(u32 *)NV_SOR_DP_HDCP_BKSV_LSB;
falcon_device_key[1] = *(u32 *)NV_SOR_TMDS_HDCP_BKSV_LSB;
falcon_device_key[2] = *(u32 *)NV_SOR_TMDS_HDCP_CN_MSB;
falcon_device_key[3] = *(u32 *)NV_SOR_TMDS_HDCP_CN_LSB;

// Clear SOR registers
*(u32 *)NV_SOR_DP_HDCP_BKSV_LSB = 0;
*(u32 *)NV_SOR_TMDS_HDCP_BKSV_LSB = 0;
*(u32 *)NV_SOR_TMDS_HDCP_CN_MSB = 0;
*(u32 *)NV_SOR_TMDS_HDCP_CN_LSB = 0;

if (out_size < 0x10)
   out_size = 0x10;

// Copy back the Falcon key
memcpy(out_buf, falcon_device_key, out_size);

// Deprogram UARTC and I2C5 clock and resets
unset_uartc_i2c5_clkrst();

// Deprogram SOR1 clock and resets
unset_sor1_clkrst1();

// Deprogram SOR1 clock and resets (no source)
unset_sor1_clkrst0();

// Deprogram QSPI clock and resets (no source)
unset_qspi_clkrst();

// Deprogram TSEC clock and resets
unset_tsec_clkrst();

// Deprogram HOST1X clock and resets
unset_host1x_clkrst()

return;

Firmware

The actual code loaded into Falcon is assembled in NVIDIA's proprietary fuc5 ISA using crypto extensions. Stored inside the first bootloader, this firmware binary is split into 4 blobs: Stage0, Stage1, Stage2 and key data.

Stage 0

During this stage key data is loaded and Stage 1 is authenticated, loaded and executed. Before returning, this stage writes back to the host (using MMIO registers) and sets the device key used by the first bootloader.

Initialization

Falcon sets up it's own stack pointer.

// Read data segment size from IO space
u32 data_seg_size = *(u32 *)UC_CAPS;
data_seg_size >>= 0x09;
data_seg_size &= 0x1FF;
data_seg_size <<= 0x08;

// Set the stack pointer
*(u32 *)sp = data_seg_size;

Stage 1 loading

u32 boot_base_addr = 0;
u32 key_data_buf[0x7C];

// Read the key data from memory
u32 key_data_addr = 0x300;
u32 key_data_size = 0x7C;
read_code(key_data_buf, key_data_addr, key_data_size);

// Read the next code segment into boot base
u32 blob1_addr = 0x400;
u32 blob1_size = *(u32 *)(key_data_buf + 0x74);
read_code(boot_base_addr, blob1_addr, blob1_size);

// Upload the next code segment into Falcon's CODE region
u32 blob1_virt_addr = 0x300;
bool use_secret = true;
upload_code(blob1_virt_addr, boot_base_addr, blob1_size, blob1_virt_addr, use_secret);

u32 boot_res = 0;
bool is_done = false;
u32 time = 0;
bool is_blob_dec = false;

while (!is_done)
{
   if (time > 4000000)
   {
      // Write boot failed (timeout) magic to FALCON_SCRATCH1
      boot_res = 0xC0C0C0C0;
      *(u32 *)FALCON_SCRATCH1 = boot_res;
      
      break;
   }
   
   // Load key version from FALCON_SCRATCH0 (bootloader sends 0x01)
   u32 key_version = *(u32 *)FALCON_SCRATCH0;

   if (key_version == 0x64)
   {
      // Skip all next stages
      boot_res = 0xB0B0B0B0;
      *(u32 *)FALCON_SCRATCH1 = boot_res;
      
      break;
   }
   else
   {
      if (key_version > 0x03)
         boot_res = 0xD0D0D0D0;    // Invalid key version
      else if (key_version == 0)
         boot_res = 0xB0B0B0B0;    // No keys used
      else
      {
         u32 key_buf[0x7C];
         
         // Copy key data
         memcpy(key_buf, key_data_buf, 0x7C);

         u32 xfer_size_flag = 0x00060000;
         u32 blob1_hash_addr = key_buf + 0x20; 

         // fuc5 crypt cauth instruction
         // Set auth_addr to 0x300 and auth_size to blob1_size
         *(u32 *)cauth = ((blob1_size << 0x10) | (0x300 >> 0x08));

         // fuc5 crypt cxset instruction
         // Set crypto transfer mode
         *(u32 *)cx = 0x02;
         
         // Transfer data from/to Falcon
	  xdst(0, (blob1_hash_addr | xfer_size_flag));
					
	  // Wait for all data loads/stores to finish
	  xdwait();

         // Jump to Stage1
         u32 stage1_res = exec_stage1(key_buf, key_version, is_blob_dec);
         is_blob_dec = true;  // Set this to prevent decrypting again

         // Set boot finish magic on success
	  if (stage1_res == 0)
            boot_res = 0xB0B0B0B0
      }
      
      // Write result to FALCON_SCRATCH1
      *(u32 *)FALCON_SCRATCH1 = boot_res;

      if (boot_res == 0xB0B0B0B0)
         is_done = true;
   }

   time++;
}

// Write Falcon device key to registers
set_device_key(key_data_buf);

return boot_res;

Stage 1

This stage is responsible for reconfiguring the Falcon's crypto co-processor and loading, decrypting, authenticating and executing Stage 2.

Crypto setup

// Clear interrupt flags
*(u8 *)flags_ie0 = 0;
*(u8 *)flags_ie1 = 0;
*(u8 *)flags_ie2 = 0;

// fuc5 crypt cxset instruction
// Set crypto transfer mode
*(u32 *)cx = 0x80;

// fuc5 crypt cauth instruction
*(u32 *)cauth &= 0x7FFFF;

// Set the target port for memory transfers
// Target will now be 0 (crypto)
xtargets(0);

// Wait for all data loads/stores to finish
xdwait();

// Wait for all code loads to finish
xcwait();

// fuc5 crypt cxset instruction
// Set crypto transfer mode
*(u32 *)cx = 0x02;

// Transfer data from/to Falcon
// This should clear all previous hashes
xdst(0, 0);

// Wait for all data loads/stores to finish
xdwait();

// Clear crypto registers
*(u32 *)c0 ^= *(u32 *)c0;
*(u32 *)c1 = *(u32 *)c0;
*(u32 *)c2 = *(u32 *)c0;
*(u32 *)c3 = *(u32 *)c0;
*(u32 *)c4 = *(u32 *)c0;
*(u32 *)c5 = *(u32 *)c0;
*(u32 *)c7 = *(u32 *)c0;

// Update engine specific IO (crypto?)
*(u32 *)0x00020E00 &= 0xEFFFF;

// Update engine specific IO (crypto?)
*(u32 *)0x00010600 |= 0x01;

u32 wait_10600 = 0;

// Wait for some device
while (wait_10600 == 0)
   wait_10600 = (*(u32 *)0x00010600 & 0x02);

// Read data segment size from IO space
u32 data_seg_size = *(u32 *)UC_CAPS;
data_seg_size >>= 0x09;
data_seg_size &= 0x1FF;
data_seg_size <<= 0x08;

// Check stack bounds
if ((*(u32 *)sp >= data_seg_size) || (*(u32 *)sp < 0x800))
  return;

// Decrypt and load Stage2
load_stage2(key_buf, key_version, is_blob_dec);

// Clear crypto registers
*(u32 *)c0 ^= *(u32 *)c0;
*(u32 *)c1 ^= *(u32 *)c1;
*(u32 *)c2 ^= *(u32 *)c2;
*(u32 *)c3 ^= *(u32 *)c3;
*(u32 *)c4 ^= *(u32 *)c4;
*(u32 *)c5 ^= *(u32 *)c5;
*(u32 *)c6 ^= *(u32 *)c6;
*(u32 *)c7 ^= *(u32 *)c7;

// Signal unknown engine
*(u32 *)0x00010300 = 0;

return;

Stage 2 loading

u32 res = 0;

u32 boot_base_addr = 0;
u32 blob0_addr = 0;
u32 blob0_size = *(u32 *)(key_buf + 0x70); 

// Load blob0 code again
read_code(boot_base_addr, blob0_addr, blob0_size);

// Generate "CODE_SIG_01" key into c4 crypto register
keygen(0, 0);

// Encrypt buffer with c4
u32 sig_key[0x10];
enc_buf(sig_key, blob0_size);

u32 src_addr = boot_base_addr;
u32 src_size = blob0_size;
u32 iv_addr = sig_key;
u32 dst_addr = sig_key;
u32 mode = 0x02;   // AES-CMAC
u32 version = 0;

// Do AES-CMAC over blob0 code
do_crypto(src_addr, src_size, iv_addr, dst_addr, mode, version);

// Compare the hashes
if (memcmp(sig_key, key_buf + 0x10, 0x10))
{
  res = 0xDEADBEEF;
  return res;
}

u32 blob1_size = *(u32 *)(key_buf + 0x74);

// Decrypt Stage2 blob if needed
if (!is_blob_dec)
{
   // Read Stage2's size from key buffer
   u32 blob2_size = *(u32 *)(key_buf + 0x78);

   // Check stack bounds
   if (*(u32 *)sp > blob2_size)
   {
      u32 boot_base_addr = 0;
      u32 blob2_virt_addr = blob0_size + blob1_size;
      u32 blob2_addr = blob2_virt_addr + 0x100;
      
      // Read Stage2's encrypted blob
      read_code(boot_base_addr, blob2_addr, blob2_size);

      // Generate "CODE_ENC_01" key into c4 crypt register
      keygen(0x01, 0x01);
      
      u32 src_addr = boot_base_addr;
      u32 src_size = blob2_size;
      u32 iv_addr = key_buf + 0x40;
      u32 dst_addr = boot_base_addr;
      u32 mode = 0;   // AES-128-CBC
      u32 version = 0;
      
      // Decrypt Stage2
      do_crypto(src_addr, src_size, iv_addr, dst_addr, mode, version);
      
      // Upload the next code segment into Falcon's CODE region
      bool use_secret = true;
      upload_code(blob2_virt_addr, boot_base_addr, blob2_size, blob2_virt_addr, use_secret);

      // Clear out the decrypted blob
      memset(boot_base_addr, 0, blob2_size);
   }
}

// fuc5 crypt cxset instruction
// Set crypto transfer mode
*(u32 *)cx = 0x02;

u32 xfer_size_flag = 0x00060000;
u32 blob2_hash_addr = key_buf + 0x30;

// Transfer data from/to Falcon
xdst(0, (blob2_hash_addr | xfer_size_flag));
				
// Wait for all data loads/stores to finish
xdwait();

// Save previous cauth value
u32 cauth_old = *(u32 *)cauth;

// fuc5 crypt cauth instruction
// Set auth_addr to blob2_virt_addr and auth_size to blob2_size
*(u32 *)cauth = ((blob2_virt_addr >> 0x08) | (blob2_size << 0x10));

u32 hovi_key_addr = 0;

// Select next stage key
if (key_version == 0x01)		// Use HOVI_EKS_01
  hovi_key_addr = key_buf + 0x50;
else if (key_version == 0x02)	        // Use HOVI_COMMON_01
  hovi_key_addr = key_buf + 0x60;
else if (key_version == 0x03)	        // Use device key
  hovi_key_addr = key_buf + 0x00;
else
  res = 0xD0D0D0D0
	
// Jump to Stage2
if (hovi_key_addr)
  res = exec_stage2(hovi_key_addr, key_version);
         
// Clear out key data
memset(key_buf, 0, 0x7C);

// Restore previous cauth value
*(u32 *)cauth = cauth_old;

return res;

Stage 2

This stage is decrypted by Stage 1 using an hardware secret. It is likely to be the main firmware code that stays running on the Falcon after the Switch's kernel is loaded (HOVI == Horizon VI?).

Key data

Small buffer stored after Stage 0's code and used across all stages.