Re: [PATCH v18 21/25] x86/cet/shstk: Handle signals for shadow stack

[Yu, Yu-cheng]

On 2/1/2021 2:53 PM, Dave Hansen wrote:
> On 1/27/21 1:25 PM, Yu-cheng Yu wrote:
> > To deliver a signal, create a shadow stack restore token and put a restore
> > token and the signal restorer address on the shadow stack.  For sigreturn,
> > verify the token and restore the shadow stack pointer.
> >
> > Introduce WRUSS, which is a kernel-mode instruction but writes directly to
> > user shadow stack.  It is used to construct the user signal stack as
> > described above.
> >
> > Introduce a signal context extension struct 'sc_ext', which is used to save
> > shadow stack restore token address and WAIT_ENDBR status.  WAIT_ENDBR will
> > be introduced later in the Indirect Branch Tracking (IBT) series, but add
> > that into sc_ext now to keep the struct stable in case the IBT series is
> > applied later.
>
> This changelog needs some work.  It's got a lot of "what" and not enough
> "why".
>
> Why do we need a token?
> What function does it serve?
> What does it protect against?
> Why do we need a signal context extension?

I will update it.

--
Yu-cheng