PR_SET_SPECULATION_CTRL(2const)

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

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <linux/prctl.h>  /* Definition of PR_* constants */
#include <sys/prctl.h>

int prctl(PR_SET_SPECULATION_CTRL, long misfeature, long val, 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.rst.

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.

SEE ALSO
prctl(2), PR_GET_SPECULATION_CTRL(2const)