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Bootloader (edit)

Revision as of 03:06, 23 January 2018

1 byte added , 03:06, 23 January 2018

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The bootloader is the binary code stored in the ARM9 and ARM11 boot ROMs and hence is ran when the 3DS is powered on. ~~It's~~ purpose is initializing hardware and loading the [[FIRM|system firmware]] from the internal [[Flash_Filesystem|NAND memory]]..

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The bootloader is the binary code stored in the ARM9 and ARM11 boot ROMs and hence is ran when the 3DS is powered on. Its purpose is initializing hardware and loading the [[FIRM|system firmware]] from the internal [[Flash_Filesystem|NAND memory]]..

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Besides NATIVE_FIRM, the bootloader is also capable of booting other firmwares (such as TWL_FIRM and AGB_FIRM). However, this will result either in a ~~japanese~~ error-screen or a system shutdown, directly after FIRM-Launching.

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Besides NATIVE_FIRM, the bootloader is also capable of booting other firmwares (such as TWL_FIRM and AGB_FIRM). However, this will result either in a Japanese error screen or a system shutdown, directly after FIRM Launching.

== Boot ROM ==

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== NAND FIRM boot ==

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Boot9 is not ~~hard-coded~~ to only handle 2 FIRM partitions: it parses all 8 NCSD partitions for this. Boot9 will attempt to use every partition listed in the NCSD which is an actual FIRM partition, in the same order listed in the NCSD, until booting one of them succeeds. Among the not-yet-processed partitions, the FIRM which has the highest value at u32 firmhdr+4 will have a FIRM-boot attempted first. Since that value is normally 0x0, the order of FIRM-partition processing is normally identical to the order of the NCSD partitions.

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Boot9 is not hardcoded to only handle 2 FIRM partitions: it parses all 8 NCSD partitions for this. Boot9 will attempt to use every partition listed in the NCSD which is an actual FIRM partition, in the same order listed in the NCSD, until booting one of them succeeds. Among the not-yet-processed partitions, the FIRM which has the highest value at u32 firmhdr+4 will have a FIRM-boot attempted first. Since that value is normally 0x0, the order of FIRM-partition processing is normally identical to the order of the NCSD partitions.

Boot9 is hard-coded for using [[AES_Registers|AES]] keyslot 0x6 for NAND crypto.

== Non-NAND FIRM boot ==

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Boot9 can also boot from non-NAND. For this a different set of RSA pubks are used(separate pubks for retail/devunit like NAND). The spiflash FIRM image for this is also encrypted with AES-CBC using a ~~normalkey~~ stored in prot_boot9(separate for retail/devunit). This encryption is basically used instead of what is used for NAND-firm-partitions. This encryption is only used for the FIRM sections, the FIRM header is used raw. The AES keyslot for this is only overwritten afterwards when booting from non-NAND fails. AES keyslot 0x3F is used for this.

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Boot9 can also boot from non-NAND. For this, a different set of RSA pubks are used(separate pubks for retail/devunit like NAND). The spiflash FIRM image for this is also encrypted with AES-CBC using a normal key stored in prot_boot9(separate for retail/devunit). This encryption is basically used instead of what is used for NAND-firm-partitions. This encryption is only used for the FIRM sections, the FIRM header is used raw. The AES keyslot for this is only overwritten afterwards when booting from non-NAND fails. AES keyslot 0x3F is used for this.

CTR_word[0] = firmimageoffset;//FIRM section offset from FIRM header

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== SDMMC ==

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Boot9 has code implemented for using SD(HC) cards, but the input deviceids used by boot9 for those functions are hard-coded for NAND. However, it is possible to use an SD(HC) card in place of the NAND if the NAND chip is first disconnected, and a SD card connected to the bus. Due to the CID being different, partitions will need to be re-encrypted and TWL mode will not work, due to the MBR being in the NCSD header. Using sighax, it may be possible to replace the NCSD header.

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Boot9 has code implemented for using SD(HC) cards, but the input deviceids used by boot9 for those functions are hard-coded for NAND. However, it is possible to use an SD(HC) card in place of the NAND if the NAND chip is first disconnected, and an SD card connected to the bus. Due to the CID being different, partitions will need to be re-encrypted and TWL mode will not work, due to the MBR being in the NCSD header. Using sighax, it may be possible to replace the NCSD header.

== Boot9 RSA keyslots ==

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* 0xffffd6e0(end-addr of the above area) size 0x40-bytes: This is the keydata used for crypting the entire OTP with keyslot 0x3f, used by main(). The first 0x20-bytes is for retail, the remaining 0x20-bytes starting at 0xffffd700 is for devunit. Chunk+0(retail=0xffffd6e0 devunit=0xffffd700) is the normalkey, chunk+0x10(retail=0xffffd6f0 devunit=0xffffd710) is the AES-IV.

* ...

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* 0xffffd760: size 0x100-bytes: First 0x80-bytes is for retail, the remaining 0x80-bytes at 0xffffd7e0 is for devunit. This 0x80-byte block is copied to 0x07ffcd00 by a Boot9 function, however that code actually does the copy in two 0x40-bytes chunks.

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* 0xffffd760: size 0x100-bytes: First 0x80-bytes is for retail, the remaining 0x80-bytes at 0xffffd7e0 is for devunit. This 0x80-byte block is copied to 0x07ffcd00 by a Boot9 function, however, that code actually does the copy in two 0x40-bytes chunks.

* 0xffffd860(end-addr of the above area) size 0x400-bytes: This is the bootrom_dataptr passed to the aes-keyinit function for retail. See the below Tools section for how this is processed.

* 0xffffdc60(end-addr of the above area) size 0x400-bytes: This is the devunit version of the above the 0x400-byte chunk. This is very last chunk of data in the boot9 data-section key-area: end addr for this area is 0xffffe060.

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...

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NAND firm-boot code-block, is described below. Note that boot9 is basically hard-coded to use deviceid NAND, not SD.

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NAND firm-boot code-block is described below. Note that boot9 is basically hard-coded to use deviceid NAND, not SD.

{

timer_updatestoredstate() is called, then the AES keyslot for NAND-FIRM is selected(0x6).

Pigeon

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