Re: [PATCH 00/10] Control Flow Enforcement - Part (3)

[Balbir Singh]

On Thu, 2018-06-14 at 07:56 -0700, Yu-cheng Yu wrote:
> On Thu, 2018-06-14 at 11:07 +1000, Balbir Singh wrote:
> > On Tue, 2018-06-12 at 08:03 -0700, Yu-cheng Yu 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()?
> > > > 
> > > 
> > > Yes.
> > 
> > I am not convinced that it would work, as we switch stacks, oveflow might
> > be an issue. I also forgot to bring up setcontext(2), I presume those
> > will get new shadow stacks
> 
> Do you mean signal stack/sigaltstack overflow or swapcontext in a signal
> handler?
>

I meant any combination of that. If there is a user space threads implementation that uses sigaltstack for switching threads

Balbir Singh.
 
> Yu-cheng
>