Suspend

When the system is suspended, it enters a low power state where the main application processor is turned off. The main DRAM state is preserved so upon resume, the kernel does not have to be reloaded.

Suspending
To suspend the system, the Vita saves the current context into a buffer and sends it to the syscon. Then it issues a syscon request to enter the low-power state.

Saving Context
The context buffer defined above is built and the physical address of the context buffer is written to Syscon memory at offset  i.e it calls sceSysconWriteForDriver with. Then it issues the syscon command to suspend the device.

Restoring Context
When resume is launched, Syscon starts first_loader, which runs second_loader, like a cold boot.

The physical address of the context buffer is read from Syscon memory at offset  i.e second_loader calls. This physical address is written to KBL Param.

Upon power up, the Boot Sequence is the same until the point where the secure kernel bootloader would jump into the non-secure kernel bootloader at. Instead, it copies the context resume function to the scratch buffer at  and the context buffer to. The resume function clears the caches and then enables the MMU. Next, it uses the context buffer to restore CP15 registers that were saved. On 1.69, it does not seem to restore,  , or. After the CP15 registers are restored, the translation tables should be restored and it then calls the resume function.

Rebooting with Patches
By abusing the way resume works, we can reboot the device into a custom firmware by patching the non-secure kernel bootloader. The general framework to do this is: first, patch the kernel bootloader in RAM to accept unsigned SELFs and load a custom kprx after. It could be the case that by the time your exploit runs the DRAM region containing the kernel loader has been wiped/reused. If so, you must use a lower level exploit to dump the loader. It may even be possible to dump the compressed version, in that case you wouldn't even need to perform cleanup. Your custom krpx will be loaded after the bare essential kernel modules are loaded (memory management, threads, file IO, etc) and it can then patch the full module loader (SceSblAuthMgr) to accept unsigned SELFs as well as any other patches.

Cleaning up non-secure Kernel Bootloader
Ideally, if we can get the original ARZL compressed version of the non-secure kernel bootloader that is extracted from, we can extract it (see ARZL), then we can load that to memory and jump to it from our resume function. However, by the time the system is in a state we control, usually that data would be corrupted. What we are left with is the non-secure kernel bootloader in the state after bootup is completed. In order to get it to run successfully again in our resume function, we need to clean up the data it uses.