On 7/22/21 1:57 PM, Yu-cheng Yu wrote:

In a signal, a task's IBT status needs to be saved to the signal frame, and
later restored in sigreturn.  For the purpose, previous versions of the
series add a new struct to the signal frame.  However, a new signal frame
format (or re-using a reserved space) introduces complex compatibility
issues.

In the discussion (see link below), Andy Lutomirski proposed using a
ucontext flag.  The approach is clean and eliminates most compatibility
issues.

However, a legacy IA32 signal frame does not have ucontext and cannot
support a uc flag.  Thus,

- Disable IBT for ia32.
- In ia32 sigreturn, verify ibt is disabled.

Acked-by: Andy Lutomirski <luto@kernel.org>