On Tuesday, June 21, 2016 10:16:21 AM CEST Kees Cook wrote: > On Tue, Jun 21, 2016 at 2:24 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote: > > On Monday, June 20, 2016 4:43:30 PM CEST Andy Lutomirski wrote: > >> > >> On my laptop, this adds about 1.5µs of overhead to task creation, > >> which seems to be mainly caused by vmalloc inefficiently allocating > >> individual pages even when a higher-order page is available on the > >> freelist. > > > > Would it help to have a fixed virtual address for the stack instead > > and map the current stack to that during a task switch, similar to > > how we handle fixmap pages? > > > > That would of course trade the allocation overhead for a task switch > > overhead, which may be better or worse. It would also give "current" > > a constant address, which may give a small performance advantage > > but may also introduce a new attack vector unless we randomize it > > again. > > Right: we don't want a fixed address. That makes attacks WAY easier. Do we care about making the address more random then? When I look at /proc/vmallocinfo, I see that allocations are all using consecutive addresses, so if you can figure out the virtual address of the stack for one process that would give you a good chance of guessing the address for the next pid. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
