OpenBSD Journal

amd64 execute-only committed to -current

Contributed by rueda on from the harder-and-harder dept.

Support for execute-only (xonly) code (on which we reported earlier) has been committed to -current by Theo de Raadt (deraadt@).

The commits were:

CVSROOT:	/cvs
Module name:	src
Changes by:	deraadt@cvs.openbsd.org	2023/01/20 09:01:04

Modified files:
	sys/arch/amd64/amd64: cpu.c locore.S pmap.c trap.c vector.S 
	sys/arch/amd64/include: cpufunc.h pte.h 

Log message:
On cpu with the PKU feature, prot=PROT_EXEC pages now create pte which
contain PG_XO, which is PKU key1.  On every exit from kernel to userland,
force the PKU register to inhibit data read against key1 memory.  On
(some) traps into the kernel if the PKU register is changed, abort the
process (processes have no reason to change the PKU register).  This
provides us with viable xonly functionality on most modern intel & AMD
cpus.  I started with a xsave-based diff from dv@, but discovered the
fpu save/restore logic wasn't a good fit and went to direct register management.
Disabled on HV (vm) systems until we know they handle PKU correctly.
ok kettenis, dv, guenther, etc

and:

CVSROOT:	/cvs
Module name:	src
Changes by:	deraadt@cvs.openbsd.org	2023/01/20 09:03:14

Modified files:
	libexec/ld.so/amd64: ld.script 

Log message:
amd64 now has xonly support via the PKU feature.  Marking ld.so exec-only
is no longer a NOP on those systems, let's do it.

As usual, testing creatively for potential breakage between now and the upcoming release will be much appreciated by the developers.


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