EPA

EPA — Add Version Array

Opcode/Instruction	Op/En	64/32 bit Mode Support	CPUID Feature Flag	Description
EAX = 0AH ENCLS[EPA]	IR	V/V	SGX1	This leaf function adds a Version Array to the EPC.

Instruction Operand Encoding ¶

Op/En	EAX	RBX	RCX
IR	EPA (In)	PT_VA (In, Constant)	Effective address of the EPC page (In)

Description ¶

This leaf function creates an empty version array in the EPC page whose logical address is given by DS:RCX, and sets up EPCM attributes for that page. At the time of execution of this instruction, the register RBX must be set to PT_VA.

The table below provides additional information on the memory parameter of EPA leaf function.

EPA Memory Parameter Semantics ¶

EPCPAGE

Write access permitted by Enclave

Concurrency Restrictions ¶

Leaf	Parameter	Base Concurrency Restrictions
Leaf	Parameter	Access	On Conflict	SGX_CONFLICT VM Exit Qualification
EPA	VA [DS:RCX]	Exclusive	#GP	EPC_PAGE_CONFLICT_EXCEPTION

Table 40-37. Base Concurrency Restrictions of EPA

Leaf	Parameter	Additional Concurrency Restrictions
		vs. EACCEPT, EACCEPTCOPY, EMODPE, EMODPR, EMODT		vs. EADD, EEXTEND, EINIT		vs. ETRACK, ETRACKC
		Access	On Conflict	Access	On Conflict	Access	On Conflict
EPA	VA [DS:RCX]	Concurrent	L	Concurrent		Concurrent

Table 40-38. Additional Concurrency Restrictions of EPA

Operation ¶

IF (RBX ≠ PT_VA or DS:RCX is not 4KByte Aligned)
    THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
    THEN #PF(DS:RCX); FI;
(* Check concurrency with other Intel SGX instructions *)
IF (Other Intel SGX instructions accessing the page)
    THEN
        IF (<<VMX non-root operation>> AND <<ENABLE_EPC_VIRTUALIZATION_EXTENSIONS>>)
            THEN
                VMCS.Exit_reason ← SGX_CONFLICT;
                VMCS.Exit_qualification.code ← EPC_PAGE_CONFLICT_EXCEPTION;
                VMCS.Exit_qualification.error ← 0;
                VMCS.Guest-physical_address ←<< translation of DS:RCX produced by paging >>;
                VMCS.Guest-linear_address ← DS:RCX;
            Deliver VMEXIT;
            ELSE
                #GP(0);
        FI;
FI;
(* Check EPC page must be empty *)
IF (EPCM(DS:RCX). VALID ≠ 0)
    THEN #PF(DS:RCX); FI;
(* Clears EPC page *)
DS:RCX[32767:0] ← 0;
EPCM(DS:RCX).PT ← PT_VA;
EPCM(DS:RCX).ENCLAVEADDRESS ← 0;
EPCM(DS:RCX).BLOCKED ← 0;
EPCM(DS:RCX).PENDING ← 0;
EPCM(DS:RCX).MODIFIED ← 0;
EPCM(DS:RCX).PR ← 0;
EPCM(DS:RCX).RWX ← 0;
EPCM(DS:RCX).VALID ← 1;

Flags Affected ¶

None

Protected Mode Exceptions ¶

#GP(0)	If a memory operand effective address is outside the DS segment limit.
	If a memory operand is not properly aligned.
	If another Intel SGX instruction is accessing the EPC page.
	If RBX is not set to PT_VA.
#PF(error	code) If a page fault occurs in accessing memory operands.
	If a memory operand is not an EPC page.
	If the EPC page is valid.

64-Bit Mode Exceptions ¶

#GP(0)	If a memory operand is non-canonical form.
	If a memory operand is not properly aligned.
	If another Intel SGX instruction is accessing the EPC page.
	If RBX is not set to PT_VA.
#PF(error	code) If a page fault occurs in accessing memory operands.
	If a memory operand is not an EPC page.
	If the EPC page is valid.