On Tue, 2018-06-12 at 09:00 -0700, Andy Lutomirski wrote: > On Tue, Jun 12, 2018 at 8:06 AM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote: > > > > On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote: > > > > > > On 08/06/18 00:37, Yu-cheng Yu wrote: > > > > This series introduces CET - Shadow stack > > > > > > > > At the high level, shadow stack is: > > > > > > > > Allocated from a task's address space with vm_flags VM_SHSTK; > > > > Its PTEs must be read-only and dirty; > > > > Fixed sized, but the default size can be changed by sys admin. > > > > > > > > For a forked child, the shadow stack is duplicated when the next > > > > shadow stack access takes place. > > > > > > > > For a pthread child, a new shadow stack is allocated. > > > > > > > > The signal handler uses the same shadow stack as the main program. > > > > > > > > > > Even with sigaltstack()? > > > > > > > > > Balbir Singh. > > > > Yes. > > > > I think we're going to need some provision to add an alternate signal > stack to handle the case where the shadow stack overflows. The shadow stack stores only return addresses; its consumption will not exceed a percentage of (program stack size + sigaltstack size) before those overflow. When that happens, there is usually very little we can do. So we set a default shadow stack size that supports certain nested calls and allow sys admin to adjust it.
