ESETCONTEXT — Set the ENCLAVECONTEXT Field in SECS

Opcode/Instruction	Op/En	64/32 bit Mode Support	CPUID Feature Flag	Description
EAX = 02H ENCLV[ESETCONTEXT]	IR	V/V	EAX[5]	This leaf function sets the ENCLAVECONTEXT field in SECS.

Instruction Operand Encoding ¶

Op/En	EAX		RCX	RDX
IR	ESETCONTEXT (In)	Return error code (Out)	Address of the destination EPC page (In, EA)	Context Value (In, EA)

Description ¶

The ESETCONTEXT leaf overwrites the ENCLAVECONTEXT field in the SECS. ECREATE and ELD of an SECS set the ENCLAVECONTEXT field in the SECS to the address of the SECS (for access later in ERDINFO). The ESETCONTEXT instruction allows a VMM to overwrite the default context value if necessary, for example, if the VMM is emulating ECREATE or ELD on behalf of the guest.

The content of RCX is an effective address of the SECS page to be updated, RDX contains the address pointing to the value to be stored in the SECS. The DS segment is used to create linear address. Segment override is not supported.

The instruction fails if:

• The operand is not properly aligned.
• RCX does not refer to an SECS page.

ESETCONTEXT Memory Parameter Semantics ¶

EPCPAGE	CONTEXT
Read access permitted by Enclave	Read/Write access permitted by Non Enclave

The instruction faults if any of the following:

ESETCONTEXT Faulting Conditions ¶

A memory operand effective address is outside the DS segment limit (32b mode).	A memory operand is not properly aligned.
DS segment is unusable (32b mode).	A page fault occurs in accessing memory operands.
A memory address is in a non-canonical form (64b mode).

Concurrency Restrictions ¶

Leaf	Parameter	Base Concurrency Restrictions
		Access	On Conflict	SGX_CONFLICT VM Exit Qualification
ESETCONTEXT	SECS [DS:RCX]	Shared	SGX_EPC_PAGE_ CONFLICT

Table 38-80. Base Concurrency Restrictions of ESETCONTEXT

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

Table 38-81. Additional Concurrency Restrictions of ESETCONTEXT

Operation ¶

Temp Variables in ESETCONTEXT Operational Flow ¶

Name	Type	Size (bits)	Description
TMP_SECS	Physical Address	64	Physical address of the SECS of the page being modified.
TMP_CONTEXT	CONTEXT	64	Data Value of CONTEXT.

ESETCONTEXT Return Value in RAX ¶

Error	Value	Description
No Error	0	ESETCONTEXT Successful.
SGX_EPC_PAGE_CONFLICT		Failure due to concurrent operation of another SGX instruction.

(* check alignment of the EPCPAGE (RCX) *)

IF (DS:RCX is not 4KByte Aligned) THEN

#GP(0); FI;

(* check that EPCPAGE (DS:RCX) is the address of an EPC page *)

IF (DS:RCX does not resolve within an EPC)THEN

#PF(DS:RCX, PFEC.SGX); FI;

(* check alignment of the CONTEXT field (RDX) *)

IF (DS:RDX is not 8Byte Aligned) THEN

#GP(0); FI;

(* Load CONTEXT into local variable *)

TMP_CONTEXT := DS:RDX

(* Check the EPC page for concurrency *)

IF (EPC page is being modified) THEN

RFLAGS.ZF := 1;

RFLAGS.CF := 0;

RAX := SGX_EPC_PAGE_CONFLICT;

goto DONE;

FI;

(* check page validity *)

IF (EPCM(DS:RCX).VALID = 0) THEN

#PF(DS:RCX, PFEC.SGX);

FI;

(* check EPC page is an SECS page *)

IF (EPCM(DS:RCX).PT is not PT_SECS) THEN

#PF(DS:RCX, PFEC.SGX);

FI;

(* load the context value into SECS(DS:RCX).ENCLAVECONTEXT *)

SECS(DS:RCX).ENCLAVECONTEXT := TMP_CONTEXT;

RAX := 0;

RFLAGS.ZF := 0;

DONE:

(* clear flags *)

RFLAGS.CF,PF,AF,OF,SF := 0;

Flags Affected ¶

ZF is set if ESETCONTEXT fails due to concurrent operation with another SGX instruction; otherwise cleared.

CF, PF, AF, OF, and SF are cleared.

Protected Mode Exceptions ¶

#GP(0)	If a memory operand effective address is outside the DS segment limit.
	If DS segment is unusable.
	If a memory operand is not properly aligned.
#PF(error	code) If a page fault occurs in accessing memory operands.

64-Bit Mode Exceptions ¶

#GP(0)	If a memory address is in a non-canonical form.
	If a memory operand is not properly aligned.
#PF(error	code) If a page fault occurs in accessing memory operands.