Untethered jailbreak for Apple's A5 devices like iPhone 4S and iPad 2 is going to be a reality as Chronic Dev-team's French hacker, Pod2g, has found a solution for the processor cache that had been troubling the hackers for a long time.
Apple users have been wondering why the hacking community is taking so long to come up with a jailbreak for A5 devices, considering the fact that they came up with a tethered jailbreak for A4 devices within 24 hours from the release of iOS 5.
The reasons may vary in the community, but the main reason for the delay is the A5 processor. As the processor is new and was released with iPad 2, there is no bootrom-level jailbreak for the processor. Whereas the bootrom-level exploit for A4 processor was found after the release iOS 4 in 2010.
Bootrom-level exploit is the only sort of exploit that is found in hardware like processor, CPU or ROM, and is unfixable by any software update because it is on the hardware and is read-only.
Apple's last processor, A4, was built upon ARM's Cortex A8 CPU which was a single core CPU, but the latest, A5 processor, is built upon ARM's Cortex A9 dual core CPU which is the biggest hurdle in finding the bootrom-level exploit in both the A5 devices.
Chronic Dev-team's Pod2g, while posting about him untethering the A5 cache, said: I'm close, but I can't figure out what happens. It certainly has something to do with the Cortex-A9 cache management.
The second thing which makes the jailbreaking difficult is A5's GPU. Apple used Imagination Technologies' (ITech) PowerVR SGX543MP2 dual core graphic processor which is an advanced product of ITech's PowerVR SGX535 used in Apple's A4 processor.
One more area where hackers will be looking to hack the A5 is memory. Both A4 and A5 processors have same L1 and L2 cache hierarchies, but the size of L2 cache of A5 is 1MB and double of A4's cache. L1 cache size for A4 and A5 32KB.
Increased size of L2 cache in A5 means more space for cache storage and more work for hackers to find a bootrom-level exploit.