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.

Context Buffer

Offset	Size	Description
0x0	0x4	Size of this structure (0x68)
0x4	0x4	Mode. Same as in smc_set_power_mode call
0x8	0x4	Some virtual address of buffer (unused?)
0xC	0x4	Virtual address of resume function called with the following arguments: (u32 TTBR1, u32 CONTEXTIDR, u32 DACR)
0x10	0x4	Saved SCTLR
0x14	0x4	Saved ACTLR
0x18	0x4	Saved CPACR
0x1C	0x4	Saved TTBR0
0x20	0x4	Saved TTBR1
0x24	0x4	Saved TTBCR
0x28	0x4	Saved DACR
0x2C	0x4	Saved PRRR
0x30	0x4	Saved NMRR
0x34	0x4	Saved VBAR
0x38	0x4	Saved CONTEXTIDR
0x3C	0x4	Saved TPIDRURW
0x40	0x4	Saved TPIDRURO
0x44	0x4	Saved TPIDRPRW
0x48	0x18	Unknown/reserved
0x60	0x8	System time

Saving Context

The context buffer defined above is built and the physical address of the context buffer is written to Syscon memory at offset 0xC i.e it calls sceSysconWriteForDriver with sceSysconWriteForDriver(0xC, &paddr, 4);. Then it issues the syscon command to suspend the device.

Resuming

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 0xC i.e second_loader calls sceSysconRead(0xC, &paddr, 4);. 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 0x51000000. Instead, it copies the context resume function to the scratch buffer at 0x1F000000 and the context buffer to 0x1F001000. 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 ACTLR, TTBR1, or DACR. 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 psp2bootconfig.skprx. 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 kernel_boot_loader.self, 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.

1.50 cleanup

Physical Address	Size	Data	Notes
0x51002024	0x4	0x0	Interrupt registering returns error if not 0
0x5100203C	0x4	0x0	Interrupt registering returns error if not 0
0x5100205C	0x4	0x0	Interrupt registering returns error if not 0
0x51002074	0x4	0x0	Interrupt registering returns error if not 0
0x51002090	0x4	0x0	Interrupt registering returns error if not 0
0x510020D0	0x4	0x0	Interrupt registering returns error if not 0
0x51002110	0x4	0x0	Interrupt registering returns error if not 0
0x510021A4	0x4	0x0	Interrupt registering returns error if not 0
0x510023FC	0x4	0x0	Interrupt registering returns error if not 0
0x51002604	0x4	0x0	Interrupt registering returns error if not 0
0x51002A40	0x4	0x0	Interrupt registering returns error if not 0
0x5102A014	0x4	0x0	Eventually gets some pointer
0x5102A020	0x4	0x1	Read Block Count (start at 1)
0x5102A024	0x4	0x1	Set to 0 after psp2bootconfig.skprx loads for hacky lock handling
0x5102A02C	0x4	0xFFFFFFFF	Memory block id after allocation
0x5102A030	0x4	0x600BF34C	Random number set after each boot to ensure integrity
0x5102A034	0x4	0xFF	Boot State ID
0x5102A050	0x4	0xFFFFFFFF	Memory block id after allocation
0x40300100	0x100	Sysroot data	Sysroot buffer copied from vaddr 0x46C0

1.69 cleanup

Physical Address	Size	Data	Notes
0x51002A40	0x4	0x0	Interrupt registering returns error if not 0
0x51002024	0x4	0x0	Interrupt registering returns error if not 0
0x5100203C	0x4	0x0	Interrupt registering returns error if not 0
0x5100205C	0x4	0x0	Interrupt registering returns error if not 0
0x51002074	0x4	0x0	Interrupt registering returns error if not 0
0x51002118	0x4	0x0	Interrupt registering returns error if not 0
0x510020D4	0x4	0x0	Interrupt registering returns error if not 0
0x51002090	0x4	0x0	Interrupt registering returns error if not 0
0x51002614	0x4	0x0	Interrupt registering returns error if not 0
0x5100240C	0x4	0x0	Interrupt registering returns error if not 0
0x510021B4	0x4	0x0	Interrupt registering returns error if not 0
0x5102A02C	0x4	0xFFFFFFFF	Memory block id after allocation
0x5102A050	0x4	0xFFFFFFFF	Memory block id after allocation
0x5102A030	0x4	0x600BF34C	Random number set after each boot to ensure integrity
0x5102A024	0x4	0x1	Set to 0 after psp2bootconfig.skprx loads for hacky lock handling
0x40300100	0x100	Sysroot data	Sysroot buffer copied from vaddr 0x46C0