Biesheuvel: Mitigating kernel risks on 32-bit ARM
Ard Biesheuvel writes
about 32-bit Arm systems on the Google Security Blog, with a focus on
why these processors are still in use and what is being done to increase
their security at the kernel level.
Preventing stack overflows from corrupting unrelated memory contents is the goal of VMAP_STACK, which we are enabling for 32-bit ARM as well. When VMAP_STACK is enabled, kernel mode stacks are allocated from the kernel heap as before, but mapped into a different part of the kernel's address space, and surrounded by guard regions, which are guaranteed to be kept unpopulated. Given that accesses to such unpopulated regions will trigger an exception, the kernel's memory management layer can step in and terminate the program as soon as a stack overflow occurs, and prevent it from causing memory corruption.