[PATCH v4] aarch64: enforce >=64K guard size

[Szabolcs Nagy]

On 14/07/18 15:02, Florian Weimer wrote:
> * Szabolcs Nagy:
> 
>> There are several compiler implementations that allow large stack
>> allocations to jump over the guard page at the end of the stack and
>> corrupt memory beyond that. See CVE-2017-1000364.
>>
>> Compilers can emit code to probe the stack such that the guard page
>> cannot be skipped, but on aarch64 the probe interval is 64K by default
>> instead of the minimum supported page size (4K).
>>
>> This patch enforces at least 64K guard on aarch64 unless the guard
>> is disabled by setting its size to 0.  For backward compatibility
>> reasons the increased guard is not reported, so it is only observable
>> by exhausting the address space or parsing /proc/self/maps on linux.
> 
> Is there anything special in the aarch64 probing sequence that
> *requires* that the guard is 64 KiB, or is it just that it is not
> effective if it is not?
> 

it's not effective (the probe interval is 64k)