On Fri 17-05-19 16:11:32, Alexander Potapenko wrote: > 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. This doesn't really explain why we need both. -- Michal Hocko SUSE Labs
