On Mon, 2019-05-20 at 18:43 -0700, David Miller wrote: > From: "Edgecombe, Rick P" <rick.p.edgecombe@xxxxxxxxx> > Date: Tue, 21 May 2019 01:20:33 +0000 > > > Should it handle executing an unmapped page gracefully? Because > > this > > change is causing that to happen much earlier. If something was > > relying > > on a cached translation to execute something it could find the > > mapping > > disappear. > > Does this work by not mapping any kernel mappings at the beginning, > and then filling in the BPF mappings in response to faults? No, nothing too fancy. It just flushes the vm mapping immediatly in vfree for execute (and RO) mappings. The only thing that happens around allocation time is setting of a new flag to tell vmalloc to do the flush. The problem before was that the pages would be freed before the execute mapping was flushed. So then when the pages got recycled, random, sometimes coming from userspace, data would be mapped as executable in the kernel by the un-flushed tlb entries.
