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 [[#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.
The Erista BCT's data is only signed after offset 0x510. 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.
The Mariko BCT's data is signed starting at offset 0x420 and encrypted starting at offset 0x480, so the [[Flash_Filesystem#Keyblob|keyblob]] system is no longer used.


= Structure =
During boot, the boot ROM parses the appropriate BCT from eMMC storage and stores a copy of it in [[Memory_layout|IRAM]].
Below is the BCT structure used by the Switch, which is a minimal variation of the Tegra 210 BCT format.


= Format =
== Erista ==
{| class="wikitable" border="1"
{| class="wikitable" border="1"
|-
|-
Line 17: Line 18:
!  Description
!  Description
|-
|-
|  0x0000
|  0x0
|  0x210
|  0x210
|  BadBlockTable
|  BadBlockTable
|  Table containing information on bad blocks
|  Table containing information on bad blocks
  0x0000: EntriesUsed (0x200)
  0x0:   EntriesUsed (0x200)
  0x0004: VirtualBlockSizeLog2 (0x0F)
  0x4:   VirtualBlockSizeLog2 (0xF)
  0x0005: BlockSizeLog2 (0x0E)
  0x5:   BlockSizeLog2 (0xE)
  0x0006: BadBlocks
  0x6:   BadBlocks
  0x0206: Reserved
  0x206: Reserved
|-
|-
|  0x0210
|  0x210
|  0x100
|  0x100
|  Key
|  Key
|  BCT RSA public key's modulus
|  BCT RSA public key's modulus
|-
|-
|  0x0310
|  0x310
|  0x110
|  0x110
|  Signature
|  Signature
|  BCT object signature
|  BCT cryptographic signature
  0x0310: CryptoHash (empty)
  0x310: CryptoHash (empty)
  0x0320: RsaPssSig
  0x320: RsaPssSig
|-
|-
|  0x0420
|  0x420
|  0x04
|  0x4
|  SecProvisioningKeyNumInsecure
|  SecProvisioningKeyNumInsecure
|  Used for Factory Secure Provisioning. Always 0.
|  Used for Factory Secure Provisioning (always 0)
|-
|-
|  0x0424
|  0x424
|  0x20
|  0x20
|  SecProvisioningKey
|  SecProvisioningKey
|  Used for Factory Secure Provisioning. Always empty.
|  Used for Factory Secure Provisioning (always 0)
|-
|-
|  0x0444
|  0x0444
|  0xC4
|  0xC4
|  [[#CustomerData|CustomerData]]
|  [[#CustomerData|CustomerData]]
|  Data block available for the customer. Used in key generation.
|  Data block available for the customer (used in key generation)
  0x0444: Reserved (0x0C bytes)
  0x444: Reserved
  0x0450: [[Flash_Filesystem#Keyblob|Keyblob]] (0xB0 bytes)
  0x450: [[Flash_Filesystem#Keyblob|Keyblob]]
  0x0500: Reserved (0x08 bytes)
  0x500: Reserved
|-
|-
|  0x0508
|  0x508
|  0x04
|  0x4
|  OdmData
|  OdmData
|  Legacy field. Unused.
|  Empty
|-
|-
|  0x050C
|  0x50C
|  0x04
|  0x4
|  Reserved
|  Reserved
|  Legacy field. Unused.
|  Empty
|-
|-
|  0x0510
|  0x510
|  0x10
|  0x10
|  RandomAesBlock
|  RandomAesBlock
|  Always empty.
|  Empty
|-
|-
|  0x0520
|  0x520
|  0x10
|  0x10
|  UniqueChipId
|  UniqueChipId
|  Always empty.
|  Empty
|-
|-
|  0x0530
|  0x530
|  0x04
|  0x4
|  BootDataVersion
|  BootDataVersion
|  Set to 0x00210001 (BOOTDATA_VERSION_T210).
|  Set to 0x210001 (BOOTDATA_VERSION_T210)
|-
|-
|  0x0534
|  0x534
|  0x04
|  0x4
|  BlockSizeLog2
|  BlockSizeLog2
|  Always 0x0E.
|  Always 0xE
|-
|-
|  0x0538
|  0x538
|  0x04
|  0x4
|  PageSizeLog2
|  PageSizeLog2
|  Always 0x09.
|  Always 0x9
|-
|-
|  0x053C
|  0x53C
|  0x04
|  0x4
|  PartitionSize
|  PartitionSize
|  Always 0x01000000.
|  Always 0x1000000
|-
|-
|  0x0540
|  0x540
|  0x04
|  0x4
|  NumParamSets
|  NumParamSets
|  Number of device parameter sets. Always 0x01.
|  Number of device parameter sets (always 0x1)
|-
|-
|  0x0544
|  0x544
|  0x04
|  0x4
|  DevType
|  DevType
|  Device type. Set to 0x04 (Sdmmc).
|  Device type (0x4 == Sdmmc)
|-
|-
|  0x0548
|  0x548
|  0x40
|  0x40
|  DevParams
|  DevParams
|  Device parameters
|  Device parameters
   0x0548: ClockDivider (0x09 == 24MHz)
   0x548: ClockDivider (0x9 == 24MHz)
   0x054C: DataWidth (0x02 == 8Bit)
   0x54C: DataWidth (0x2 == 8Bit)
|-
|-
|  0x0588
|  0x588
|  0x04
|  0x4
|  NumSdramSets
|  NumSdramSets
|  Number of SDRAM parameter sets. Always set to 0, but parameters are used despite this.
|  Number of SDRAM parameter sets (always set to 0, but parameters are used despite this)
|-
|-
|  0x058C
|  0x58C
|  0x768
|  0x768
|  SdramParams0
|  SdramParams0
|  Default values filled in.
|  Default values filled in
|-
|-
|  0x0CF4
|  0xCF4
|  0x768
|  0x768
|  SdramParams1
|  SdramParams1
|  Default values filled in.
|  Default values filled in
|-
|-
|  0x145C
|  0x145C
|  0x768
|  0x768
|  SdramParams2
|  SdramParams2
|  Default values filled in.
|  Default values filled in
|-
|-
|  0x1BC4
|  0x1BC4
|  0x768
|  0x768
|  SdramParams3
|  SdramParams3
|  Default values filled in.
|  Default values filled in
|-
|-
|  0x232C
|  0x232C
|  0x04
|  0x4
|  BootLoadersUsed
|  BootLoadersUsed
|  Number of bootloaders installed. Always 0x02 (maximum is 0x04).
|  Number of bootloaders installed (always 0x2, maximum is 0x4)
|-
|-
|  0x2330
|  0x2330
|  0x12C
|  0x12C
|  [[#BootLoader0|BootLoader0]]
|  [[#BootLoader0|BootLoader0]]
|  Configuration parameters for bootloader 0 (normal).
|  Configuration parameters for bootloader 0 (main)
  0x2330: Version (variable)
  0x2330: Version (variable)
  0x2334: StartBlock (0x00000040)
  0x2334: StartBlock (0x40 for BootImagePackage, 0x100 for BootImagePackageSafe)
  0x2338: StartPage (0x00000000)
  0x2338: StartPage (0)
  0x233C: Length (variable)
  0x233C: Length (variable)
  0x2340: LoadAddress (0x40010000)
  0x2340: LoadAddress (0x40010000)
  0x2344: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
  0x2344: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
  0x2348: Attribute (0x00000000)
  0x2348: Attribute (0 for BootImagePackage, 1 for BootImagePackageSafe)
  0x234C: CryptoHash (empty)
  0x234C: CryptoHash (empty)
  0x235C: RsaPssSig
  0x235C: RsaPssSig
Line 161: Line 162:
|  0x12C
|  0x12C
|  BootLoader1
|  BootLoader1
|  Configuration parameters for bootloader 1 (safe mode).
|  Configuration parameters for bootloader 1 (backup)
  0x245C: Version (variable)
  0x245C: Version (variable)
  0x2460: StartBlock (0x00000050)
  0x2460: StartBlock (0x50 for BootImagePackage, 0x110 for BootImagePackageSafe)
  0x2464: StartPage (0x00000000)
  0x2464: StartPage (0)
  0x2468: Length (variable)
  0x2468: Length (variable)
  0x246C: LoadAddress (0x40010000)
  0x246C: LoadAddress (0x40010000)
  0x2470: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
  0x2470: EntryPoint (0x40010020 for 1.0.0-3.0.2, 0x40010040 for 4.0.0+)
  0x2474: Attribute (0x00000000)
  0x2474: Attribute (0 for BootImagePackage, 1 for BootImagePackageSafe)
  0x2478: CryptoHash (empty)
  0x2478: CryptoHash (empty)
  0x2488: RsaPssSig
  0x2488: RsaPssSig
Line 175: Line 176:
|  0x12C
|  0x12C
|  BootLoader2
|  BootLoader2
|  Reserved space for bootloader 2 (unused).
|  Reserved space for bootloader 2 (unused)
|-
|-
|  0x26B4
|  0x26B4
|  0x12C
|  0x12C
|  BootLoader3
|  BootLoader3
|  Reserved space for bootloader 3 (unused).
|  Reserved space for bootloader 3 (unused)
|-
|-
|  0x27E0
|  0x27E0
|  0x01
|  0x1
|  EnableFailBack
|  EnableFailBack
|  Always 0.
|  Always 0
|-
|-
|  0x27E1
|  0x27E1
|  0x04
|  0x4
|  SecureJtagControl
|  SecureJtagControl
|  Always 0.
|  Always 0
|-
|-
|  0x27E5
|  0x27E5
|  0x04
|  0x4
|  SecProvisioningKeyNumSecure
|  SecProvisioningKeyNumSecure
|  Used for Factory Secure Provisioning. Always 0.
|  Used for Factory Secure Provisioning (always 0)
|-
|-
|  0x27E9
|  0x27E9
|  0x12
|  0x12
|  Reserved
|  Reserved
|  Always starts with 0x80000000 (NVBOOT padding pattern).
|  Always starts with 0x80000000 (NVBOOT padding pattern)
|-
|-
|  0x27FB
|  0x27FB
|  0x05
|  0x5
|  Padding
|  Padding
|  Empty. Not part of BCT data.
|  Empty
|}
|}


== CustomerData ==
=== 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 229: Line 230:
|}
|}


== BootLoader0 ==
=== BootLoader0 ===
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 controls which keyblob is used, where 0x1 is the first one. See [[Cryptosystem]] for the keyblobs used by each system-version.
 
== Mariko ==
{| class="wikitable" border="1"
|-
!  Offset
!  Size
!  Field
!  Description
|-
|  0x0
|  0x210
|  Pcp
|  BCT public cryptographic parameters
0x0:  KeySize
0x4:  Reserved
0x10:  PublicKeyModulus
0x110: PublicKeyExponent
|-
|  0x210
|  0x110
|  Signature
|  BCT cryptographic signature
0x210: CryptoHash (empty)
0x220: RsaPssSig
|-
|  0x320
|  0x20
|  SecProvisioningKey
|  Used for Factory Secure Provisioning (always 0)
|-
|  0x340
|  0x4
|  SecProvisioningKeyNumInsecure
|  Used for Factory Secure Provisioning (always 0)
|-
|  0x344
|  0xC
|  Padding
|  Empty
|-
|  0x350
|  0xD0
|  CustomerData
|  Data block available for the customer
|-
|  0x420
|  0x10
|  RandomAesBlock
| 
|-
|  0x430
|  0x10
| 
|  Empty
|-
|  0x440
|  0x40
| 
|  Empty
|-
|  0x480
|  0x10
|  RandomAesBlock2
| 
|-
|  0x490
|  0x10
|  UniqueChipId
|  Empty
|-
|  0x4A0
|  0x4
|  BootDataVersion
|  Set to 0x210001 (BOOTDATA_VERSION_T210)
|-
|  0x4A4
|  0x4
|  BlockSizeLog2
|  Always 0xE
|-
|  0x4A8
|  0x4
|  PageSizeLog2
|  Always 0x9
|-
|  0x4AC
|  0x4
|  PartitionSize
|  Always 0x1000000
|-
|  0x4B0
|  0x4
|  NumParamSets
|  Number of device parameter sets (always 0x1)
|-
|  0x4B4
|  0x4
|  DevType
|  Device type (0x4 == Sdmmc)
|-
|  0x4B8
|  0x40
|  DevParams
|  Device parameters
|-
|  0x4F8
|  0x4
|  NumSdramSets
|  Number of SDRAM parameter sets (always set to 0, but parameters are used despite this)
|-
|  0x4FC
|  0x838
|  SdramParams0
|  Default values filled in
|-
|  0xD34
|  0x838
|  SdramParams1
|  Default values filled in
|-
|  0x156C
|  0x838
|  SdramParams2
|  Default values filled in
|-
|  0x1DA4
|  0x838
|  SdramParams3
|  Default values filled in
|-
|  0x25DC
|  0x04
|  BootLoadersUsed
|  Number of bootloaders installed (always 0x2, maximum is 0x4)
|-
|  0x25E0
|  0x10
|  BootLoader0
|  Configuration parameters for bootloader 0 (main)
0x25E0: StartBlock (0x40 for BootImagePackage, 0x100 for BootImagePackageSafe)
0x25E4: StartPage (0)
0x25E8: Version (variable)
0x25EC: Reserved
|-
|  0x25F0
|  0x10
|  BootLoader1
|  Configuration parameters for bootloader 1 (backup)
0x25F0: StartBlock (0x50 for BootImagePackage, 0x110 for BootImagePackageSafe)
0x25F4: StartPage (0)
0x25F8: Version (variable)
0x25FC: Reserved
|-
|  0x2600
|  0x10
|  BootLoader2
|  Reserved space for bootloader 2 (unused)
|-
|  0x2610
|  0x10
|  BootLoader3
|  Reserved space for bootloader 3 (unused)
|-
|  0x2620
|  0x4
|  SecureDebugControlNoneEcid
|  Empty
|-
|  0x2624
|  0x4
|  SecureDebugControlEcid
|  Empty
|-
|  0x2628
|  0x10
| 
|  Empty
|-
|  0x2638
|  0x40
| 
|  Empty
|-
|  0x2678
|  0x4
|  SecProvisioningKeyNumSecure
|  Used for Factory Secure Provisioning (always 0)
|-
|  0x267C
|  0x184
|  Reserved
|  Always starts with 0x80000000 (NVBOOT padding pattern)
|}
Retrieved from "https://switchbrew.org/wiki/BCT"