Speculation Control
===================
-Quite some CPUs have speculation related misfeatures which are in fact
-vulnerabilites causing data leaks in various forms even accross privilege
-domains.
+Quite some CPUs have speculation-related misfeatures which are in
+fact vulnerabilities causing data leaks in various forms even across
+privilege domains.
The kernel provides mitigation for such vulnerabilities in various
-forms. Some of these mitigations are compile time configurable and some on
-the kernel command line.
+forms. Some of these mitigations are compile-time configurable and some
+can be supplied on the kernel command line.
There is also a class of mitigations which are very expensive, but they can
be restricted to a certain set of processes or tasks in controlled
Bit Define Description
==== ===================== ===================================================
0 PR_SPEC_PRCTL Mitigation can be controlled per task by
- PR_SET_SPECULATION_CTRL
+ PR_SET_SPECULATION_CTRL.
1 PR_SPEC_ENABLE The speculation feature is enabled, mitigation is
- disabled
+ disabled.
2 PR_SPEC_DISABLE The speculation feature is disabled, mitigation is
- enabled
+ enabled.
3 PR_SPEC_FORCE_DISABLE Same as PR_SPEC_DISABLE, but cannot be undone. A
subsequent prctl(..., PR_SPEC_ENABLE) will fail.
==== ===================== ===================================================
If all bits are 0 the CPU is not affected by the speculation misfeature.
-If PR_SPEC_PRCTL is set, then the per task control of the mitigation is
+If PR_SPEC_PRCTL is set, then the per-task control of the mitigation is
available. If not set, prctl(PR_SET_SPECULATION_CTRL) for the speculation
misfeature will fail.
Value Meaning
======= =================================================================
EINVAL The prctl is not implemented by the architecture or unused
- prctl(2) arguments are not 0
+ prctl(2) arguments are not 0.
-ENODEV arg2 is selecting a not supported speculation misfeature
+ENODEV arg2 is selecting a not supported speculation misfeature.
======= =================================================================
PR_SET_SPECULATION_CTRL error codes
0 Success
ERANGE arg3 is incorrect, i.e. it's neither PR_SPEC_ENABLE nor
- PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE
+ PR_SPEC_DISABLE nor PR_SPEC_FORCE_DISABLE.
ENXIO Control of the selected speculation misfeature is not possible.
See PR_GET_SPECULATION_CTRL.