On Fri, Dec 01, 2023 at 11:50:25AM +0000, Szabolcs Nagy wrote:

The 11/30/2023 21:51, Mark Brown wrote:

quoted

The concern Rick raised was that allowing user to pick the exact shadow
stack pointer would allow userspace to corrupt or reuse the stack of an
existing thread by starting a new thread with the shadow stack pointing
into the existing shadow stack of that thread.  While in isolation

note that this can be prevented by map_shadow_stack adding
a token that clone3 verifies.

That would make it impossible to reuse the shadow stack once the token
is overwritten which does move the needle more towards making doing the
mapping separately pure overhead.