EMODPE — Extend an EPC Page Permissions

Opcode/Instruction	Op/En	64/32 bit Mode Support	CPUID Feature Flag	Description
EAX = 06H ENCLU[EMODPE]	IR	V/V	SGX2	This leaf function extends the access rights of an existing EPC page.

Instruction Operand Encoding ¶

Op/En	EAX	RBX	RCX
IR	EMODPE (In)	Address of a SECINFO (In)	Address of the destination EPC page (In)

Description ¶

This leaf function extends the access rights associated with an existing EPC page in the running enclave. THE RWX bits of the SECINFO parameter are treated as a permissions mask; supplying a value that does not extend the page permissions will have no effect. This instruction leaf can only be executed when inside the enclave.

RBX contains the effective address of a SECINFO structure while RCX contains the effective address of an EPC page. The table below provides additional information on the memory parameter of the EMODPE leaf function.

EMODPE Memory Parameter Semantics ¶

SECINFO	EPCPAGE
Read access permitted by Non Enclave	Read access permitted by Enclave

The instruction faults if any of the following:

EMODPE Faulting Conditions ¶

The operands are not properly aligned.	If security attributes of the SECINFO page make the page inaccessible.
The EPC page is locked by another thread.	RBX does not contain an effective address in an EPC page in the running enclave.
The EPC page is not valid.	RCX does not contain an effective address of an EPC page in the running enclave.
SECINFO contains an invalid request.

Concurrency Restrictions ¶

Leaf	Parameter	Base Concurrency Restrictions
		Access	On Conflict	SGX_CONFLICT VM Exit Qualification
EMODPE	Target [DS:RCX]	Concurrent
	SECINFO [DS:RBX]	Concurrent

Table 38-70. Base Concurrency Restrictions of EMODPE

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
EMODPE	Target [DS:RCX]	Exclusive	#GP	Concurrent		Concurrent
	SECINFO [DS:RBX]	Concurrent		Concurrent		Concurrent

Table 38-71. Additional Concurrency Restrictions of EMODPE

Operation ¶

Temp Variables in EMODPE Operational Flow ¶

Name	Type	Size (bits)	Description
SCRATCH_SECINFO	SECINFO	512	Scratch storage for holding the contents of DS:RBX.

IF (DS:RBX is not 64Byte Aligned)

THEN #GP(0); FI;

IF (DS:RCX is not 4KByte Aligned)

THEN #GP(0); FI;

IF ((DS:RBX is not within CR_ELRANGE) or (DS:RCX is not within CR_ELRANGE) )

THEN #GP(0); FI;

IF (DS:RBX does not resolve within an EPC)

THEN #PF(DS:RBX); FI;

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

THEN #PF(DS:RCX); FI;

IF ( (EPCM(DS:RBX).VALID = 0) or (EPCM(DS:RBX).R = 0) or (EPCM(DS:RBX).PENDING ≠ 0) or (EPCM(DS:RBX).MODIFIED ≠ 0) or

(EPCM(DS:RBX).BLOCKED ≠ 0) or (EPCM(DS:RBX).PT ≠ PT_REG) or (EPCM(DS:RBX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or

(EPCM(DS:RBX).ENCLAVEADDRESS ≠ (DS:RBX & ~0xFFF)) )

THEN #PF(DS:RBX); FI;

SCRATCH_SECINFO := DS:RBX;

(* Check for misconfigured SECINFO flags*)

IF (SCRATCH_SECINFO reserved fields are not zero )

THEN #GP(0); FI;

(* Check security attributes of the EPC page *)

IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PENDING ≠ 0) or (EPCM(DS:RCX).MODIFIED ≠ 0) or

(EPCM(DS:RCX).BLOCKED ≠ 0) or (EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) )

THEN #PF(DS:RCX); FI;

(* Check the EPC page for concurrency *)

IF (EPC page in use by another SGX2 instruction)

THEN #GP(0); FI;

(* Re-Check security attributes of the EPC page *)

IF ( (EPCM(DS:RCX).VALID = 0) or (EPCM(DS:RCX).PENDING ≠ 0) or (EPCM(DS:RCX).MODIFIED ≠ 0) or

(EPCM(DS:RCX).PT ≠ PT_REG) or (EPCM(DS:RCX).ENCLAVESECS ≠ CR_ACTIVE_SECS) or

(EPCM(DS:RCX).ENCLAVEADDRESS ≠ DS:RCX))

THEN #PF(DS:RCX); FI;

(* Check for misconfigured SECINFO flags*)

IF ( (EPCM(DS:RCX).R = 0) and (SCRATCH_SECINFO.FLAGS.R = 0) and (SCRATCH_SECINFO.FLAGS.W ≠ 0) )

(* Update EPCM permissions *)

EPCM(DS:RCX).R := EPCM(DS:RCX).R | SCRATCH_SECINFO.FLAGS.R;

EPCM(DS:RCX).W := EPCM(DS:RCX).W | SCRATCH_SECINFO.FLAGS.W;

EPCM(DS:RCX).X := EPCM(DS:RCX).X | SCRATCH_SECINFO.FLAGS.X;

Flags Affected ¶

None

Protected Mode Exceptions ¶

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

64-Bit Mode Exceptions ¶

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