On Fri, Aug 16, 2024 at 12:09:01PM +0100, Catalin Marinas wrote: > On Thu, Aug 01, 2024 at 01:06:32PM +0100, Mark Brown wrote: > > +* EL0 GCS entries with bit 63 set are reserved for use, one such use is defined > Maybe "reserved for specific uses". The proposed sentenced feels like > it's missing something. Actually we removed the usage of bit 63 so I'll just drop this. > > +* When a new thread is created by a thread which has GCS enabled then a > > + new Guarded Control Stack will be allocated for the new thread with > > + half the size of the standard stack. > Is the half size still the case? It also seems a bit inconsistent to > have RLIMIT_STACK when GCS is enabled and half the stack size when a new > thread is created. Yes, this predates the rebase onto clone3() - I'll update. > [...] > > +* When a thread is freed the Guarded Control Stack initially allocated for > > + that thread will be freed. Note carefully that if the stack has been > > + switched this may not be the stack currently in use by the thread. > Is this true for shadow stacks explicitly allocated by the user with > map_shadow_stack()? It is only true for the stacks allocaeted by the kernel, if we didn't allocate a stack we don't free it. > > +* The signal handler will use the same GCS as the interrupted context. > I assume this is true even with sigaltstack. Not easy to have > alternative shadow stack without additional ABI. Yes.
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