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
|