Bootloaders¶

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.

Devices configurations¶

Device and documentation	Freedom situation	Boot order
Samsung Nexus S (i902x)	Proprietary, Signed on the tested devices	?->USB->?->eMMC->?
Samsung Galaxy S2 (i9100)	Proprietary, probably Signed	?
Samsung Galaxy Tab 2	Proprietary, signed	?->USB->?->eMMC->?
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

System on a chip¶

SOC and documentation	Freedom situation
OMAP	No known bug
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 use code signature * Boot from USB is possible thanks to fusee_gelee * Code can be appended to the bootrom by writing in a fuse area. Could that be used to disable code signature ?
IMX 5 and 6	* Not all devices are signed * Thanks to Ref_QBVR2017-0001.txt it's possible to bypass signatures anyway, and maybe load code through USB too

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
  • Booting_chain
• https://www.theiphonewiki.com/ has a list of Bootrom security issues for apple devices.
• Ti Nspire ? RSA exponent issues?

See also

• Upstream