Re: [PATCH v8 00/38] arm64/gcs: Provide support for GCS in userspace

Edgecombe, Rick P
2024-02-20T23:30:57Z

On Tue, 2024-02-20 at 20:14 +0000, Mark Brown wrote:
> > Hmm, could the shadow stack underflow onto the real stack then? Not
> > sure how bad that is. INCSSP (incrementing the SSP register on x86)
> > loops are not rare so it seems like something that could happen.
>
> Yes, they'd trash any pages of normal stack they touch as they do so
> but
> otherwise seems similar to overflow.

I was thinking in the normal buffer overflow case there is a guard gap
at the end of the stack, but in this case the shadow stack is directly
adjacent to the regular stack. It's probably a minor point.