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)