pr_get_speculation_ctrl(2const)

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Options · 8

PR_SPEC_STORE_BYPASS	Get the state of the speculative store bypass misfeature.
PR_SPEC_INDIRECT_BRANCH (since Linux 4.20)	Get the state of the indirect branch speculation misfeature.
PR_SPEC_PRCTL	Mitigation can be controlled per thread by PR_SET_SPECULATION_CTRL(2const).
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).
ENODEV	The kernel or CPU does not support the requested speculation misfeature.

NAME

PR_GET_SPECULATION_CTRL - get the state of a speculation misfeature for the calling thread

LIBRARY

Standard C library (libc, -lc)

SYNOPSIS

bash

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

bash

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

DESCRIPTION

Return the state of the speculation misfeature specified in misfeature.

Currently, misfeature must be one of:

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

The return value uses bits 0-4 with the following meaning:

PR_SPEC_PRCTL: Mitigation can be controlled per thread by PR_SET_SPECULATION_CTRL(2const).
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).

If all bits are 0, then the CPU is not affected by the speculation misfeature.

If PR_SPEC_PRCTL is set, then per-thread control of the mitigation is available. If not set, PR_SET_SPECULATION_CTRL(2const) for the speculation misfeature will fail.

RETURN VALUE

On success, PR_GET_SPECULATION_CTRL returns the nonnegative value described above. 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.

STANDARDS

Linux.

HISTORY

Linux 4.17.