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 buffer (0x68)
|
| 0x4 | 0x4 | Same as unk field of syscon_reset_device call
|
| 0x8 | 0x4 | Some virtual address of buffer (unused?) |
| 0xC | 0x4 | Virtual address of resume function |
| 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/unused |
| 0x60 | 0x8 | System time |
Saving Context
The context buffer defined above is built and the physical address of the buffer is sent to the Syscon with command 12. It calls Send command with syscon_send_command(12, &paddr, 4). Then it issues the command to suspend the device.
Resuming
Upon power up, the Boot Sequence is the same until the point where the secure kernel loader would jump into the non-secure kernel loader 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 loader. The general framework to do this is: first, patch the kernel loader 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 libraries are loaded (memory management, threads, file IO, etc) and it can then patch the full module loader to accept unsigned SELFs as well as any other patches.
Cleaning up Bootloader
Ideally, if we can get the original compressed version of the non-secure bootloader that is extracted from kernel_boot_loader.self, 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 loader 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
|