On 11/29, Tycho Andersen wrote:

/*
 * These should never be seen by user programs.  To return one of ERESTART*
 * codes, signal_pending() MUST be set.  Note that ptrace can observe these
 * at syscall exit tracing, but they will never be left for the debugged user
 * process to see.
 */
#define ERESTARTSYS     512

So basically, if you respond with -ERESTARTSYS with no signal pending, you'll
leak it to userspace.

Yes,

It turns out this is already possible with
SECCOMP_RET_TRAP (and probably ptrace alone,

Yes,

The question is: do we care?

I think we do not care, debugger can do anything with the tracee.

Oleg.