Nintendo Switch Brew

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The Switch's BCT is included in the firmware package titles (0100000000000819 and 010000000000081A) and is installed into eMMC storage's [[Flash_Filesystem#Boot_Partitions|boot partition 0]]. A total of four BCT copies can be installed into the system: normal, normal backup, safe mode and safe mode backup.
The Switch's BCT is included in the firmware package titles (0100000000000819 and 010000000000081A) and is installed into eMMC storage's [[Flash_Filesystem#Boot_Partitions|boot partition 0]]. A total of four BCT copies can be installed into the system: normal, normal backup, safe mode and safe mode backup.


By design, the BCT's data is only signed after offset 0x0510. Therefore, regions like [[#customer_data|customer_data]] can be freely modified without resigning. This is done by [[NS_Services|NS]] when injecting a new [[Flash_Filesystem#Keyblob|keyblob]] during a system update, for example.
By design, the BCT's data is only signed after offset 0x0510. Therefore, regions like [[#CustomerData|CustomerData]] can be freely modified without resigning. This is done by [[NS_Services|NS]] when injecting a new [[Flash_Filesystem#Keyblob|keyblob]] during a system update, for example.


During boot, the boot ROM parses the appropriate BCT from eMMC storage and stores a copy of it in IRAM at address 0x40000000.
During boot, the boot ROM parses the appropriate BCT from eMMC storage and stores a copy of it in IRAM at address 0x40000000.


= Structure =
= Structure =
== NAND ==
Below is the BCT structure used by the Switch, which is a minimal variation of the Tegra 210 BCT format.
Below is the BCT structure used by the Switch, which is a minimal variation of the Tegra 210 BCT format.


Line 20: Line 19:
|  0x0000
|  0x0000
|  0x210
|  0x210
|  bad_block_table
|  BadBlockTable
|  Table containing information on bad blocks
|  Table containing information on bad blocks
  0x0000: num_entries (0x200)
  0x0000: EntriesUsed (0x200)
  0x0004: virtual_block_size (0x0F)
  0x0004: VirtualBlockSizeLog2 (0x0F)
  0x0005: block_size (0x0E)
  0x0005: BlockSizeLog2 (0x0E)
  0x0006: bad_blocks
  0x0006: BadBlocks
  0x0206: reserved
  0x0206: Reserved
|-
|-
|  0x0210
|  0x0210
|  0x100
|  0x100
|  bct_key
|  Key
|  BCT RSA key modulus
|  BCT RSA public key's modulus
|-
|-
|  0x0310
|  0x0310
|  0x110
|  0x110
|  bct_signature
|  Signature
|  BCT object signature
|  BCT object signature
  0x0310: hash (empty)
  0x0310: CryptoHash (empty)
  0x0320: rsa_pss_signature
  0x0320: RsaPssSig
|-
|-
|  0x0420
|  0x0420
|  0x04
|  0x04
|  sec_provisioning_key_num_insecure
|  SecProvisioningKeyNumInsecure
|  Used for Factory Secure Provisioning. Always 0.
|  Used for Factory Secure Provisioning. Always 0.
|-
|-
|  0x0424
|  0x0424
|  0x20
|  0x20
|  sec_provisioning_key
|  SecProvisioningKey
|  Used for Factory Secure Provisioning. Always empty.
|  Used for Factory Secure Provisioning. Always empty.
|-
|-
|  0x0444
|  0x0444
|  0xC4
|  0xC4
|  [[#customer_data|customer_data]]
|  [[#CustomerData|CustomerData]]
|  Data block available for the customer. Used in key generation.
|  Data block available for the customer. Used in key generation.
  0x0444: padding_0x0C
  0x0444: Reserved (0x0C bytes)
  0x0450: keyblob_0xB0
  0x0450: [[Flash_Filesystem#Keyblob|Keyblob]] (0xB0 bytes)
  0x0500: padding_0x08
  0x0500: Reserved (0x08 bytes)
|-
|-
|  0x0508
|  0x0508
|  0x04
|  0x04
|  odm_data
|  OdmData
|  Legacy field. Unused.
|  Legacy field. Unused.
|-
|-
|  0x050C
|  0x050C
|  0x04
|  0x04
|  reserved0
|  Reserved
|  Legacy field. Unused.
|  Legacy field. Unused.
|-
|-
|  0x0510
|  0x0510
|  0x10
|  0x10
|  random_aes_block
|  RandomAesBlock
|  Always empty.
|  Always empty.
|-
|-
|  0x0520
|  0x0520
|  0x10
|  0x10
|  unique_chip_id
|  UniqueChipId
|  Always empty.
|  Always empty.
|-
|-
|  0x0530
|  0x0530
|  0x04
|  0x04
|  boot_data_version
|  BootDataVersion
|  Set to 0x00210001 (BOOTDATA_VERSION_T210).
|  Set to 0x00210001 (BOOTDATA_VERSION_T210).
|-
|-
|  0x0534
|  0x0534
|  0x04
|  0x04
|  block_size_log2
|  BlockSizeLog2
|  Always 0x0E.
|  Always 0x0E.
|-
|-
|  0x0538
|  0x0538
|  0x04
|  0x04
|  page_size_log2
|  PageSizeLog2
|  Always 0x09.
|  Always 0x09.
|-
|-
|  0x053C
|  0x053C
|  0x04
|  0x04
|  partition_size
|  PartitionSize
|  Always 0x01000000.
|  Always 0x01000000.
|-
|-
|  0x0540
|  0x0540
|  0x04
|  0x04
|  num_param_sets
|  NumParamSets
|  Number of device parameter sets. Always 0x01.
|  Number of device parameter sets. Always 0x01.
|-
|-
|  0x0544
|  0x0544
|  0x04
|  0x04
|  dev_type
|  DevType
|  Device type. Set to 0x04 (dev_type_sdmmc).
|  Device type. Set to 0x04 (Sdmmc).
|-
|-
|  0x0548
|  0x0548
|  0x40
|  0x40
|  dev_params
|  DevParams
| Device parameters
| Device parameters
   0x0548: sdmmc_clock_divider (0x09 == 24MHz)
   0x0548: ClockDivider (0x09 == 24MHz)
   0x054C: sdmmc_data_width (0x02 == sdmmc_data_width_8bit)
   0x054C: DataWidth (0x02 == 8Bit)
|-
|-
|  0x0588
|  0x0588
|  0x04
|  0x04
|  num_sdram_sets
|  NumSdramSets
|  Number of SDRAM parameter sets. Always set to 0 (parameters unused).
|  Number of SDRAM parameter sets. Always set to 0, but parameters are used despite this.
|-
|-
|  0x058C
|  0x058C
|  0x768
|  0x768
|  sdram_params0
|  SdramParams0
|  Default values filled in, but not used
|  Default values filled in.
|-
|-
|  0x0CF4
|  0x0CF4
|  0x768
|  0x768
|  sdram_params1
|  SdramParams1
|  Default values filled in, but not used
|  Default values filled in.
|-
|-
|  0x145C
|  0x145C
|  0x768
|  0x768
|  sdram_params2
|  SdramParams2
|  Default values filled in, but not used
|  Default values filled in.
|-
|-
|  0x1BC4
|  0x1BC4
|  0x768
|  0x768
|  sdram_params3
|  SdramParams3
|  Default values filled in, but not used
|  Default values filled in.
|-
|-
|  0x232C
|  0x232C
|  0x04
|  0x04
|  num_bootloaders
|  BootLoadersUsed
|  Number of bootloaders installed. Always 0x02 (maximum is 0x04).
|  Number of bootloaders installed. Always 0x02 (maximum is 0x04).
|-
|-
|  0x2330
|  0x2330
|  0x12C
|  0x12C
|  [[#bootloader0_info|bootloader0_info]]
|  [[#BootLoader0|BootLoader0]]
|  Configuration parameters for bootloader 0 (normal).
|  Configuration parameters for bootloader 0 (normal).
  0x2330: version (variable)
  0x2330: Version (variable)
  0x2334: start_block (0x00000040)
  0x2334: StartBlock (0x00000040)
  0x2338: start_page (0x00000000)
  0x2338: StartPage (0x00000000)
  0x233C: length (variable)
  0x233C: Length (variable)
  0x2340: load_addr (0x40010000)
  0x2340: LoadAddress (0x40010000)
  0x2344: entry_point (0x40010020)
  0x2344: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
  0x2348: attribute (0x00000000)
  0x2348: Attribute (0x00000000)
  0x234C: bootloader0_hash (empty)
  0x234C: CryptoHash (empty)
  0x235C: bootloader0_rsa_pss_signature
  0x235C: RsaPssSig
|-
|-
|  0x245C
|  0x245C
|  0x12C
|  0x12C
|  bootloader1_info
|  BootLoader1
|  Configuration parameters for bootloader 1 (safe mode).
|  Configuration parameters for bootloader 1 (safe mode).
  0x245C: version (variable)
  0x245C: Version (variable)
  0x2460: start_block (0x00000050)
  0x2460: StartBlock (0x00000050)
  0x2464: start_page (0x00000000)
  0x2464: StartPage (0x00000000)
  0x2468: length (variable)
  0x2468: Length (variable)
  0x246C: load_addr (0x40010000)
  0x246C: LoadAddress (0x40010000)
  0x2470: entry_point (0x40010020)
  0x2470: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
  0x2474: attribute (0x00000000)
  0x2474: Attribute (0x00000000)
  0x2478: bootloader1_hash (empty)
  0x2478: CryptoHash (empty)
  0x2488: bootloader1_rsa_pss_signature
  0x2488: RsaPssSig
|-
|-
|  0x2588
|  0x2588
|  0x258
|  0x12C
|  reserved1
|  BootLoader2
|  Reserved space for bootloaders 2 and 3 (currently unused).
|  Reserved space for bootloader 2 (unused).
|-
|  0x26B4
|  0x12C
|  BootLoader3
|  Reserved space for bootloader 3 (unused).
|-
|-
|  0x27E0
|  0x27E0
|  0x01
|  0x01
|  enable_fail_back
|  EnableFailBack
|  Always 0.
|  Always 0.
|-
|-
|  0x27E1
|  0x27E1
|  0x04
|  0x04
|  secure_debug_control
|  SecureJtagControl
|  Always 0.
|  Always 0.
|-
|-
|  0x27E5
|  0x27E5
|  0x04
|  0x04
|  sec_provisioning_key_num_secure
|  SecProvisioningKeyNumSecure
|  Used for Factory Secure Provisioning. Always 0.
|  Used for Factory Secure Provisioning. Always 0.
|-
|-
|  0x27E9
|  0x27E9
|  0x12
|  0x12
|  reserved2
|  Reserved
|  Always starts with 0x80000000 (NVBOOT padding pattern).
|  Always starts with 0x80000000 (NVBOOT padding pattern).
|-
|-
|  0x27FB
|  0x27FB
|  0x05
|  0x05
|  padding
|  Padding
|  Empty. Not part of BCT data.
|  Empty. Not part of BCT data.
|-
|}
|}


=== customer_data ===
== CustomerData ==
This data block is ignored by the boot ROM, therefore is available for the programmer to use freely.
This data block is ignored by the boot ROM, therefore is available for the programmer to use freely.
The Switch uses 0xB0 bytes of this area, at offset 0x0450, to store the active [[Flash_Filesystem#Keyblob|keyblob]]. All remaining bytes are zero.
The Switch uses 0xB0 bytes of this area, at offset 0x0450, to store the active [[Flash_Filesystem#Keyblob|keyblob]]. All remaining bytes are zero.
Line 223: Line 226:
| 0x80
| 0x80
| 0x10  
| 0x10  
| [[Package1#Stage_1|Stage 1]] key
| [[Package1#PK11_Blob|PK11]] key
|}
|}


=== bootloader0_info ===
== BootLoader0 ==
==== 1.0.0 - 2.3.0 ====
The version field controls which keyblob is used, where 0x01 is the first one. See [[Cryptosystem]] for the keyblobs used by each system-version.
The version field is set to 0x01, meaning that the first keyblob is to be used.
 
==== 3.0.0 ====
The version field was changed to 0x02, meaning that the second keyblob is now used.
 
==== 3.0.1 ====
The version field was changed to 0x03, meaning that the third keyblob is now used.
 
== IRAM ==
When copied to IRAM, the BCT has an additional header as follows.
 
{| class="wikitable" border="1"
|-
!  Offset
!  Size
!  Field
!  Description
|-
|  0x00
|  0x50
|  bct_global_header
|  Contains pointers to actual BCT data.
0x4C: bct_data_addr (address of the actual BCT)
|-
|  0x50
|  0x18
|  bootloader0_header
|  Unknown structure.
0x00: is_active (if set to 0x01, bootloader0 is used)
|-
|  0x68
|  0x18
|  bootloader1_header
|  Unknown structure.
0x00: is_active (if set to 0x01, bootloader1 is used)
|-
|  0x80
|  0x18
|  bootloader2_header
|  Unknown structure.
0x00: is_active (if set to 0x01, bootloader2 is used)
|-
|  0x98
|  0x18
|  bootloader3_header
|  Unknown structure.
0x00: is_active (if set to 0x01, bootloader3 is used)
|-
|}
Retrieved from "https://switchbrew.org/wiki/BCT"