On Fri, May 17, 2019 at 4:04 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > On Tue 14-05-19 16:35:34, Alexander Potapenko wrote: > > The new options are needed to prevent possible information leaks and > > make control-flow bugs that depend on uninitialized values more > > deterministic. > > > > init_on_alloc=1 makes the kernel initialize newly allocated pages and heap > > objects with zeroes. Initialization is done at allocation time at the > > places where checks for __GFP_ZERO are performed. > > > > init_on_free=1 makes the kernel initialize freed pages and heap objects > > with zeroes upon their deletion. This helps to ensure sensitive data > > doesn't leak via use-after-free accesses. > > Why do we need both? The later is more robust because even free memory > cannot be sniffed and the overhead might be shifted from the allocation > context (e.g. to RCU) but why cannot we stick to a single model? init_on_free appears to be slower because of cache effects. It's several % in the best case vs. <1% for init_on_alloc. > -- > Michal Hocko > SUSE Labs -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
