EBLOCK

SGX INSTRUCTION REFERENCES EBLOCK — Mark a page in EPC as Blocked

Opcode/ Instruction	Op/En	64/32 bit Mode Support	CPUID Feature Flag	Description
EAX = 09H ENCLS[EBLOCK]	IR	V/V	SGX1	This leaf function marks a page in the EPC as blocked.

Instruction Operand Encoding

Op/En	EAX		RCX
IR	EBLOCK (In)	Return error code (Out)	Effective address of the EPC page (In)

Description

This leaf function causes an EPC page to be marked as BLOCKED. This instruction can only be executed when current privilege level is 0.

The content of RCX is an effective address of an EPC page. The DS segment is used to create linear address. Segment override is not supported.

An error code is returned in RAX.

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

EBLOCK Memory Parameter Semantics

EPCPAGE

Read/Write access permitted by Enclave

The error codes are:

Table 40-12. EBLOCK Return Value in RAX

Error Code (see Table 40-4)	Description
No Error	EBLOCK successful.
SGX_BLKSTATE	Page already blocked. This value is used to indicate to a VMM that the page was already in BLOCKED state as a result of EBLOCK and thus will need to be restored to this state when it is eventually reloaded (using ELDB).
SGX_ENTRYEPOCH_LOCKED	SECS locked for Entry Epoch update. This value indicates that an ETRACK is currently executing on the SECS. The EBLOCK should be reattempted.
SGX_NOTBLOCKABLE	Page type is not one which can be blocked.
SGX_PG_INVLD	Page is not valid and cannot be blocked.
SGX_EPC_PAGE_CONFLICT	Page is being written by EADD, EAUG, ECREATE, ELDU/B, EMODT, or EWB.

Concurrency Restrictions

Table 40-13. Base Concurrency Restrictions of EBLOCK

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

Vol. 3D 40-25 SGX INSTRUCTION REFERENCES

Table 40-14. Additional Concurrency Restrictions of EBLOCK

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
EBLOCK	Target [DS:RCX]	Concurrent		Concurrent		Concurrent

Operation

Temp Variables in EBLOCK Operational Flow

<table>
	<tr>
		<td><b>Name</b></td>
		<td><b>Type</b></td>
		<td><b>Size (Bits)</b></td>
		<td><b>Description</b></td>
	</tr>
	<tr>
		<td>TMP_BLKSTATE</td>
		<td>Integer</td>
		<td>64</td>
		<td>Page is already blocked.</td>
	</tr>
</table>

IF (DS:RCX is not 4KByte Aligned)
    THEN #GP(0); FI;
IF (DS:RCX does not resolve within an EPC)
    THEN #PF(DS:RCX); FI;
RFLAGS.ZF,CF,PF,AF,OF,SF ← 0;
RAX← 0;
(* Check the EPC page for concurrency*)
IF (EPC page in use)
    THEN
        RFLAGS.ZF ← 1;
        RAX← SGX_EPC_PAGE_CONFLICT;
        GOTO DONE;
FI;
IF (EPCM(DS:RCX). VALID = 0)
    THEN 
        RFLAGS.ZF ← 1;
        RAX← SGX_PG_INVLD;
        GOTO DONE;
FI;
IF ( (EPCM(DS:RCX).PT ≠ PT_REG) and (EPCM(DS:RCX).PT ≠ PT_TCS) and (EPCM(DS:RCX).PT ≠ PT_TRIM) )
    THEN 
        RFLAGS.CF ← 1;
        IF (EPCM(DS:RCX).PT = PT_SECS) 
            THEN RAX← SGX_PG_IS_SECS;
            ELSE RAX← SGX_NOTBLOCKABLE;
        FI;
        GOTO DONE;
FI;
(* Check if the page is already blocked and report blocked state *)
TMP_BLKSTATE ← EPCM(DS:RCX).BLOCKED;
40-26 Vol. 3D
                            SGX INSTRUCTION REFERENCES
(* at this point, the page must be valid and PT_TCS or PT_REG or PT_TRIM*)
IF (TMP_BLKSTATE = 1) 
    THEN 
        RFLAGS.CF ← 1;
        RAX← SGX_BLKSTATE;
    ELSE
        EPCM(DS:RCX).BLOCKED ← 1
FI;
DONE:

Flags Affected

Sets ZF if SECS is in use or invalid, otherwise cleared. Sets CF if page is BLOCKED or not blockable, otherwise cleared. Clears PF, AF, OF, SF.

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 the specified EPC resource is in use.

#PF(error code) If a page fault occurs in accessing memory operands. If a memory operand is not an EPC page.

64-Bit Mode Exceptions

#GP(0) If a memory operand is non-canonical form. If a memory operand is not properly aligned. If the specified EPC resource is in use.

#PF(error code) If a page fault occurs in accessing memory operands. If a memory operand is not an EPC page.

Vol. 3D 40-27

---

Source: Intel® Architecture Software Developer's Manual (May 2018)
Generated: 5-6-2018