EEXIT — Exits an Enclave

Opcode/Op/En 64/32 CPUID Description Instruction bit Mode Feature Support Flag EAX = 04H IR V/V SGX1 This leaf function is used to exit an enclave. ENCLU[EEXIT]

Instruction Operand Encoding ¶

Op/En	EAX	RBX	RCX
IR	EEXIT (In)	Target address outside the enclave (In)	Address of the current AEP (Out)

Description ¶

The ENCLU[EEXIT] instruction exits the currently executing enclave and branches to the location specified in RBX. RCX receives the current AEP. If RBX is not within the CS (32-bit mode) or is not canonical (64-bit mode) a #GP(0) results.

EEXIT Memory Parameter Semantics ¶

Target Address

Non-Enclave read and execute access

If RBX specifies an address that is inside the enclave, the instruction will complete normally. The fetch of the next instruction will occur in non-enclave mode, but will attempt to fetch from inside the enclave. This fetch returns a fixed data pattern.

If secrets are contained in any registers, it is responsibility of enclave software to clear those registers.

If XCR0 was modified on enclave entry, it is restored to the value it had at the time of the most recent EENTER or ERESUME.

If the enclave is opt-out, RFLAGS.TF is loaded from the value previously saved on EENTER.

Code and data breakpoints are unsuppressed.

Performance monitoring counters are unsuppressed.

Concurrency Restrictions ¶

Leaf	Parameter	Base Concurrency Restrictions
			On Conflict
EEXIT		Concurrent

Table 38-64. Base Concurrency Restrictions of EEXIT

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
EEXIT		Concurrent		Concurrent		Concurrent

Table 38-65. Additional Concurrency Restrictions of EEXIT

Operation ¶

Temp Variables in EEXIT Operational Flow ¶

Name	Type	Size (Bits)	Description
TMP_RIP	Effective Address	32/64	Saved copy of CRIP for use when creating LBR.

TMP_MODE64 := ((IA32_EFER.LMA = 1) && (CS.L = 1));

IF (TMP_MODE64 = 1)

THEN

IF (RBX is not canonical) THEN #GP(0); FI;

ELSE

IF (RBX > CS limit) THEN #GP(0); FI;

FI;

TMP_RIP := CRIP;

RIP := RBX;

(* Return current AEP in RCX *)

RCX := CR_TCS_PA.AEP;

(* Do the FS/GS swap *)

FS.selector := CR_SAVE_FS.selector;

FS.base := CR_SAVE_FS.base;

FS.limit := CR_SAVE_FS.limit;

FS.access_rights := CR_SAVE_FS.access_rights;

GS.selector := CR_SAVE_GS.selector;

GS.base := CR_SAVE_GS.base;

GS.limit := CR_SAVE_GS.limit;

GS.access_rights := CR_SAVE_GS.access_rights;

(* Restore XCR0 if needed *)

IF (CR4.OSXSAVE = 1)

XCR0 := CR_SAVE__XCR0;

FI;

Unsuppress_all_code_breakpoints_that_are_outside_ELRANGE;

IF (CR_DBGOPTIN = 0)

THEN

UnSuppress_all_code_breakpoints_that_overlap_with_ELRANGE;

Restore suppressed breakpoint matches;

RFLAGS.TF := CR_SAVE_TF;

UnSuppress_montior_trap_flag;

UnSuppress_LBR_Generation;

UnSuppress_performance monitoring_activity;

Restore performance monitoring counter AnyThread demotion to MyThread in enclave back to AnyThread

FI;

IF RFLAGS.TF = 1

THEN Pend Single-Step #DB at the end of EEXIT;

FI;

IF the “monitor trap flag” VM-execution control is set

THEN pend a MTF VM exit at the end of EEXIT;

FI;

IF (CPUID.(EAX=12H, ECX=1):EAX[6] = 1)

THEN

(* Record PREVSSP *)

IF (IA32_U_CET.SH_STK_EN == 1)

THEN CR_TCS_PA.PREVSSP = SSP; FI;

FI;

IF ((CPUID.(EAX=7H, ECX=0):EDX[CET_IBT] = 1) OR (CPUID.(EAX=7, ECX=0):ECX[CET_SS] = 1)

THEN

(* Restore enclosing app’s CET state from the save registers *)

IA32_U_CET := CR_SAVE_IA32_U_CET;

IF CPUID.(EAX=07H, ECX=00h):ECX[CET_SS] = 1

THEN SSP := CR_SAVE_SSP; FI;

(* Update enclosing app’s TRACKER if enclosing app has indirect branch tracking enabled *)

IF (CR4.CET = 1 AND IA32_U_CET.ENDBR_EN = 1)

THEN

IA32_U_CET.TRACKER := WAIT_FOR_ENDBRANCH;

IA32_U_CET.SUPPRESS := 0

FI;

FI;

CR_ENCLAVE_MODE := 0;

CR_TCS_PA.STATE := INACTIVE;

(* Assure consistent translations *)

Flush_linear_context;

Flags Affected ¶

RFLAGS.TF is restored from the value previously saved in EENTER or ERESUME.

Protected Mode Exceptions ¶

#GP(0)	If executed outside an enclave.
	If RBX is outside the CS segment.
#PF(error	code) If a page fault occurs in accessing memory.

64-Bit Mode Exceptions ¶

#GP(0)	If executed outside an enclave.
	If RBX is not canonical.
#PF(error	code) If a page fault occurs in accessing memory operands.