Re: [PATCH 06/10] x86/cet: Add arch_prctl functions for shadow stack

[Andy Lutomirski]

> On Jun 19, 2018, at 1:12 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> 
>> On Tue, Jun 19, 2018 at 10:20 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> 
>>> On Jun 19, 2018, at 10:07 AM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>>> 
>>> Does it provide anything beyond what PR_DUMPABLE does?
>> 
>> What do you mean?
> 
> I was just going by the name of it. I wasn't sure what "ptrace CET
> lock" meant, so I was trying to understand if it was another "you
> can't ptrace me" toggle, and if so, wouldn't it be redundant with
> PR_SET_DUMPABLE = 0, etc.
> 

No, other way around. The valid CET states are on/unlocked, off/unlocked, on/locked, off/locked. arch_prctl can freely the state unless locked. ptrace can change it no matter what.  The lock is to prevent the existence of a gadget to disable CET (unless the gadget involves ptrace, but I donât think thatâs a real concern).