3 ms·
I once wrote something that would hard lock cortex-A8 but not the cortex-A9 we shipped on. To my knowledge, nobody tracked down why our app, once exfiltrated fr
by bobmcnamara 2y ago
I once wrote something that would hard lock cortex-A8 but not the cortex-A9 we shipped on. To my knowledge, nobody tracked down why our app, once exfiltrated from our device, would crash slightly older phones.
- pm215 2y agoWere you exploiting an A8 erratum, or detecting "this is an A8" somehow and then making it barf in a less processor specific way?
- bobmcnamara 2y agoA8 erratum. This was ages ago, but if I recall you could place a thumb2 instruction straddling two pages, only one of which was loaded in the TLBs. If you got everything right, the A8 would hang without trapping. Edit: it was errata #657417, long since scrubbed from arm.com
- pm215 2y agoThe A8 errata doc is at https://developer.arm.com/documentation/prdc008070/latest/ https://developer.arm.com/documentation/prdc008070/latest/ these days and does have a description of 657417 with enough detail to make writing a reproducer possible. Instructions crossing page boundaries are tricky beasts :-)
- bobmcnamara 2y agoWell look at that! I had searched Google and arm.com for that number. This was definitely it.
- AtlasBarfed 2y agoSo they'll patch around it. You're just making your software worthless in the long run for some value probably less than 5 years, or creating a fun problem for an emu hacker. Most of the significant losses to piracy monetarily isn't emulation, it's the chippers/mods that bypass cloned media copy protection. Which emulator authors have a lot more control over in bypassing
- pm215 2y agoIf it hardlocked an A8 but not an A9, chances are very high that an emulator would run it with no problem, because nobody deliberately tries to emulate the kind of CPU bug that lets an app hardlock the CPU. GP appears to have been interested in deterring people from running their code on non-authorised real hardware at the time, not targeting emulator users.
- bobmcnamara 2y agoBingo! Didn't want someone running new product's app on old product's hardware. Company was new to building non-RTOS devices which were tightly hardware bound, wanted similar type restrictions.
- mikestew 2y agoYou assume an anti-piracy attempt when GP, from my reading, made no such statement. More of a mystery, but who cares because the problem hardware wasn’t what they shipped on.
- cwillu 2y agoThey used the word exfiltrate, it's not a stretch.