On Fri, Oct 19, 2018 at 8:49 AM, Will Deacon <will.deacon@xxxxxxx> wrote: > On Fri, Oct 19, 2018 at 08:36:45AM -0700, Kees Cook wrote: >> On Fri, Oct 19, 2018 at 4:24 AM, Will Deacon <will.deacon@xxxxxxx> wrote: >> > FWIW: I think we should be entertaining a prctl() interface to use a new >> > key on a per-thread basis. Obviously, this would need to be used with care >> > (e.g. you'd fork(); use the prctl() and then you'd better not return from >> > the calling function!). >> > >> > Assuming we want this (Kees -- I was under the impression that everything in >> > Android would end up with the same key otherwise?), then the question is >> > do we want: >> > >> > - prctl() get/set operations for the key, or >> > - prctl() set_random_key operation, or >> > - both of the above? >> > >> > Part of the answer to that may lie in the requirements of CRIU, where I >> > strongly suspect they need explicit get/set operations, although these >> > could be gated on CONFIG_CHECKPOINT_RESTORE=y. >> >> Oh CRIU. Yikes. I'd like the get/set to be gated by the CONFIG, yes. >> No reason to allow explicit access to the key (and selected algo) if >> we don't have to. > > Makes sense. > >> As for per-thread or not, having a "pick a new key now" prctl() sounds >> good, but I'd like to have an eye toward having it just be "automatic" >> on clone(). > > I thought about that too, but we're out of clone() flags afaict and there's > no arch hook in there. We could add yet another clone syscall, but yuck (and > I reckon viro would kill us). > > Or are you saying that we could infer the behaviour from the existing set > of flags? I mean if it's starting a new thread, it should get a new key automatically, just like the ssp canary happens in dup_task_struct(). (Or did I miss some context for why that's not possible?) -Kees -- Kees Cook Pixel Security
