ARM Exception Vector Info Leak

This vulnerability is used by evasi0n in order to defeat KASLR. Since iOS6 the kernel base address is randomized at 2^9 possible locations. Actually it is not fully randomized due to the ARM vector table residing at a fixed address. The vector table is held at address zero and at runtime relocated to  by setting the V-bit in CP15 c1. The following ARM vector table entries exist:

evasi0n calls the Data Abort exception from a separate thread and catches the exception. In the exception handler,  is saved to   and leaks the base address because this exception was called from.

In the exception handler it is also possible to get 4 bytes at a chosen address, so this is additionally an info leak for arbitrary memory.