Add STKGAP disable fctl flag.

[kib]

Summary

This also fixes a bug where p_osrel and p_fctl0 were obliterated by failed execve(2) attempt, to be committed separately.

[markj]

sys/kern/kern_exec.c

398 ↗

(On Diff #64363)

Perhaps sysctl_kern_proc_osrel() should look up the process with PGET_NOTINEXEC.

402 ↗

(On Diff #64363)

Doesn't this need to happen after imgp is initialized below?

877 ↗

(On Diff #64363)

Why write imgp->proc instead of p?

[kib]

sys/kern/kern_exec.c

398 ↗

(On Diff #64363)

I do not think so, it would cause spurious failures from the sysctl. Would NOTINEXEC was implemented as a wait for transition to non-execing state, then perhaps. But I think it is fine to see transient move of p_osrel during failing exec.

[kib]

Only use imgp after it is initialized, and use p later.

[markj]

sys/kern/kern_exec.c

410 ↗

(On Diff #64398)

We can use p here too.

[markj]

sys/kern/kern_exec.c

398 ↗

(On Diff #64363)

I was thinking that since the sysctl can update the p_osrel, its update may be clobbered when we roll back after a failed exec. But of course this race is possible even when the exec is successful.

[kib]

One more 'p'.