wrpkru

Write Protection Key Rights

WRPKRU

Writes EAX/EDX to PKRU register.

Pseudocode Operation

// Write EAX to PKRU, EDX must be zero
IF (EDX ≠ 0) THEN
  #GP(0); // General Protection Fault
ELSE
  PKRU ← EAX;
END;
// No flags modified; instruction is serializing

Encoding

Binary Layout

Format Legacy

Opcode NP 0F 01 EF

Extension PKU

Operands

Reference

View in Intel® 64 and IA-32 Architectures SDM ↗ Intel® SDM

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
NP 0F 01 EF	WRPKRU	ZO	V/V	OSPKE	Writes EAX into PKRU.

Description

Writes the value of EAX into PKRU. ECX and EDX must be 0 when WRPKRU is executed; otherwise, a generalprotection exception (#GP) occurs. WRPKRU can be executed only if CR4.PKE = 1; otherwise, an invalid-opcode exception (#UD) occurs. Software can discover the value of CR4.PKE by examining CPUID.07H.00H:ECX.OSPKE[4]. On processors that support the Intel 64 Architecture, the high-order 32-bits of RCX, RDX, and RAX are ignored. WRPKRU will never execute speculatively. Memory accesses affected by PKRU register will not execute (even speculatively) until all prior executions of WRPKRU have completed execution and updated the PKRU register.

Operation

IF (ECX = 0 AND EDX = 0)
THEN PKRU := EAX;
ELSE #GP(0);
FI;

Flags Affected

None. C/C++ Compiler Intrinsic Equivalent WRPKRU void _wrpkru(uint32_t);

Exceptions

Protected Mode Exceptions

#GP(0) If ECX ≠ 0. If EDX ≠ 0. #UD If the LOCK prefix is used. If CR4.PKE = 0.

Real-Address Mode Exceptions

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions