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.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.

SEE ALSO

       prctl(2), PR_GET_SPECULATION_CTRL(2const)

Linux man-pages 6.9.1                              2024-06-01                    PR_SET_SPECULATION_CTRL(2const)