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

[Edgecombe, Rick P]

On Tue, 2024-02-20 at 18:11 -0800, Rick Edgecombe wrote:
> Some specific cases that were still open were longjmp()ing off of a
> custom userspace threading library stack, which may not have left a
> token behind when it jumped to a new stack. And also, potentially off
> of an alt shadow stack in the future, depending on whether it leaves
> a
> restore token when handling a signal. (the problem there, is if there
> is no room to leave it).

Ah, I remember the other one. If the token on the target shadow stack
is at the end of the shadow stack, it may not be able to handle pushing
a shadow stack signal frame if a signal hits while is unwinding through
the token. As in, where normal longjmp() is direct transition, in this
case the longjmp() operation can be temporarily in a place where a
signal cannot be handled.