Memory layout
Userspace
The userspace virtual address space has 38 bits. It seems that when the IPC protocol was designed, it was only 36 bits leading to a weird encoding format.
There are several regions maintained by the kernel, each one starting at the upper bits bit37-21 randomized:
- Main binary region.
- Heap region.
- Stack mapping region, available from SVC#svcGetInfo.
For the stack mapping region, the userland randomizes a page-offset where to start inside the region. This adds some additional entropy.
Binaries mapped by RO seems to be mapped randomly everywhere in the entire address space. The random base address for each NRO has bits 37-12 randomized, unlike the main binary region.
For all binaries(main area / NROs), the R-- section is always located immediately after R-X. The RW- section is always located immediately after the R-- section. Hence, there's no extra randomization / guard-pages for these sections.
TLS
This is the 0x200-byte thread-local-storage, the base address is loaded via ARM threadid register tpidrro_el0.
| Offset | Size | Description |
|---|---|---|
| 0x0 | 0x100 | IPC command buffer |
| 0x100 | 0xF8 | ? |
| 0x1F8 | 0x8 | Address of threadctx+0x58. |
Thread context
This is the structure of the 0x228-byte threadctx used by official userland software.
| Offset | Size | Description |
|---|---|---|
| 0x0 | 0xA8 | ? |
| 0xA8 | 0x8 | Address of the stack-bottom-mirror which the thread was created with. |
| 0xB0 | 0x8 | Size of the stack. |
| 0xB8 | 0x178 | ? |