On Tue, 2018-06-12 at 09:00 -0700, Andy Lutomirski wrote:

On Tue, Jun 12, 2018 at 8:06 AM Yu-cheng Yu [off-list ref] wrote:

quoted

On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote:

quoted

On 08/06/18 00:37, Yu-cheng Yu wrote:

quoted

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.