b4c82b3b07
still active. Map userspace portion of VA in the PTI kernel-mode page table as non-executable. This way, if we ever miss reloading ucr3 into %cr3 on the return to usermode, the process traps instead of executing in potentially vulnerable setup. Catch the condition of such trap and verify user-mode %cr3, which is saved by page fault handler. I peek this trick in some article about Linux implementation. Reviewed by: alc, markj (previous version) Sponsored by: The FreeBSD Foundation MFC after: 12 days DIfferential revision: https://reviews.freebsd.org/D13956
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