Replicant

h1. Bootloaders

h2. Introduction

In order to run free software bootloaders, we need the ability to run the code we want at boot.

However in most smartphones and many tablets use code signature at boot, which prevent us to run free software bootloader.

In practice:

* Some system on a chip either don't implement code signature or the implementation is not used or tested.

* For some other system on a chip, it's up to the device vendor to choose to implement code signature or not.

* For some system on a chip, we don't know any devices not enforcing code signature, but we don't know who decided to enforce the code signature.

h2. Devices configurations

|_. Device and documentation |_. Freedom situation |_. Boot order |

| [[NexusSI902xBootloader| Samsung Nexus S (i902x)]] | Proprietary, Signed on the tested devices | ?->USB->?->eMMC->? |

| [[I9100Bootloader| Samsung Galaxy S2 (i9100)]] | Proprietary, probably Signed | ? |

| [[GalaxyTab2Bootloader| Samsung Galaxy Tab 2]] | Proprietary, signed | ?->USB->?->eMMC->? |

| [[OptimusBlackBootloader| LG Optimus black (p970)]] | unsigned, can be replaced with upstream u-boot | eMMC(MMC2)->USB |

| Galaxy SIII (I9300)

Galaxy SIII 4G (I9305)

Galaxy Note II (N7100)

Galaxy Note II 4G (N7105) | * Proprietary, Signed

* There is work in progress to understand if we can avoid the signature | ?->eMMC->?->USB->? |

| Golden Delicous GTA04 | unsigned, free software | * Aux not pressed during boot: ?

* Aux pressed during boot: ?->SD->?->NAND

SYS_BOOT0 = 1

SYS_BOOT1 = 1

SYS_BOOT2 = 1

SYS_BOOT3 = 1

SYS_BOOT4 = 1

SYS_BOOT5 = AUX button

SYS_BOOT6 = 1 

But cannot find Reference manual for the DM370 |

h2. System on a chip

|_. SOC and documentation |_. Freedom situation |

| [[Exynos4Bootrom|Exynos 4]] | * Some or all devices are signed

* work in progress to understand if it's possible to bypass the signature |

| [[BroadcomVideoCore]] | The SOCs have the ability to check signatures |

| [[TegraBootrom]] | * Not all devices are signed

* Boot from USB is possible thanks to "fusee_gelee":https://github.com/Qyriad/fusee-launcher/blob/master/report/fusee_gelee.md |

| IMX 5 and 6 | * Not all devices are signed

* Thanks to "Ref_QBVR2017-0001.txt":https://github.com/f-secure-foundry/usbarmory/blob/master/software/secure_boot/Security_Advisory-Ref_QBVR2017-0001.txt it's possible to bypass signatures anyway, and maybe load code through USB too |

h2. Other attempts that involves bypassing the bootrom

There have been several security issues in bootrom, which can enable to run fully free software bootloaders, that are under the user control, even on devices that are configured to enforce bootloader signatures.

The most interesting security issues is when it enables to just replace the nonfree bootloader by a free bootloader that is controlled by the user.

While being able to load a free bootloader through USB is nice, it's not enough per se as it has usability concerns: it's not convenient to need another computer each time you need to power on your smartphone or tablet.

It seems that according to a "youtube video":https://www.youtube.com/watch?v=REx_qSTulJM small enough USB dongles exist that implemented fusee_gelee for the Nitendo Switch.

On tegras, as the bootrom can also be patched as part of it ends up being in the fuse memory region, it may be possible to patch the bootrom to bypass the code signature and not need such dongles.

|_. Affected SOCs |_. Type |_. Link |

Other links to cathegorize:

* http://www.droid-developers.org : This attempts to run user code on several Motorolla smartphones. It includes analysis of the boot chain:

** "Application_Processor_Boot_ROM":www.droid-developers.org/wiki/Application_Processor_Boot_ROM

** "Booting_chain":http://www.droid-developers.org/wiki/Booting_chain

* https://www.theiphonewiki.com/ has a list of "Bootrom security issues":https://www.theiphonewiki.com/wiki/Bootrom for apple devices.

* "Ti Nspire":https://hackspire.org ? RSA exponent issues?

== See also ==

* [[Upstream]]