pr_set_speculation_ctrl(2const)

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Options · 10

PR_SPEC_STORE_BYPASS	Set the state of the speculative store bypass misfeature.
PR_SPEC_INDIRECT_BRANCH (since Linux 4.20)	Set the state of the indirect branch speculation misfeature.
PR_SPEC_ENABLE	The speculation feature is enabled, mitigation is disabled.
PR_SPEC_DISABLE	The speculation feature is disabled, mitigation is enabled.
PR_SPEC_FORCE_DISABLE	Same as PR_SPEC_DISABLE, but cannot be undone.
PR_SPEC_DISABLE_NOEXEC (since Linux 5.1)	Same as PR_SPEC_DISABLE, but the state will be cleared on execve(2). Currently only supported for PR_SPEC_STORE_BYPASS.
ENODEV	The kernel or CPU does not support the requested speculation misfeature.
ENXIO	The control of the selected speculation misfeature is not possible. See PR_GET_SPECULATION_CTRL for the bit fields to determine which option is available.
EPERM	The speculation was disabled with PR_SPEC_FORCE_DISABLE and caller tried to enable it again.
ERANGE	misfeature is not a valid value.

NAME

PR_SET_SPECULATION_CTRL - set the state of a speculation misfeature for the calling thread

SYNOPSIS

bash

#include <linux/prctl.h>\n  /* Definition of \nPR_*\n constants */
\n#include <sys/prctl.h>

bash

int prctl(PR_SET_SPECULATION_CTRL, long \nmisfeature\n, long \nval\n, 0L, 0L);

DESCRIPTION

Sets the state of the speculation misfeature specified in misfeature. The speculation-misfeature settings are per-thread attributes.

Currently, misfeature must be one of:

PR_SPEC_STORE_BYPASS: Set the state of the speculative store bypass misfeature.
PR_SPEC_INDIRECT_BRANCH (since Linux 4.20): Set the state of the indirect branch speculation misfeature.

The val argument is used to hand in the control value, which is one of the following:

PR_SPEC_ENABLE: The speculation feature is enabled, mitigation is disabled.
PR_SPEC_DISABLE: The speculation feature is disabled, mitigation is enabled.
PR_SPEC_FORCE_DISABLE: Same as PR_SPEC_DISABLE, but cannot be undone.
PR_SPEC_DISABLE_NOEXEC (since Linux 5.1): Same as PR_SPEC_DISABLE, but the state will be cleared on execve(2). Currently only supported for PR_SPEC_STORE_BYPASS.

The speculation feature can also be controlled by the spec_store_bypass_disable boot parameter. This parameter may enforce a read-only policy which will result in the prctl() call failing with the error ENXIO. For further details, see the kernel source file Documentation/admin-guide/kernel-parameters.txt.

RETURN VALUE

On success, 0 is returned. On error, -1 is returned, and errno is set to indicate the error.

ERRORS

ENODEV: The kernel or CPU does not support the requested speculation misfeature.
ENXIO: The control of the selected speculation misfeature is not possible. See PR_GET_SPECULATION_CTRL for the bit fields to determine which option is available.
EPERM: The speculation was disabled with PR_SPEC_FORCE_DISABLE and caller tried to enable it again.
ERANGE: misfeature is not a valid value.

STANDARDS

Linux.

HISTORY

Linux 4.17.