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Henk-Jan Lebbink edited this page Jun 5, 2018 · 2 revisions

SGX INSTRUCTION REFERENCES EMODT — Change the Type of an EPC Page

Opcode/ Instruction Op/En 64/32 bit Mode Support CPUID Feature Flag Description
EAX = 0FH ENCLS[EMODT] IR V/V SGX2 This leaf function changes the type of an existing EPC page.

Instruction Operand Encoding

Op/En EAX RBX RCX
IR EMODT (In) Return Error Code (Out) Address of a SECINFO (In) Address of the destination EPC page (In)

Description

This leaf function modifies the type of an EPC page. The security attributes are configured to prevent access to the EPC page at its new type until a corresponding invocation of the EACCEPT leaf confirms the modification. This instruction can only be executed when current privilege level is 0.

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 EMODT leaf function.

EMODT Memory Parameter Semantics

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

The instruction faults if any of the following:

EMODT Faulting Conditions

The operands are not properly aligned. If unsupported security attributes are set.
The Enclave is not initialized. SECS is locked by another thread.
The EPC page is locked by another thread. RCX does not contain an effective address of an EPC page in the running enclave.
The EPC page is not valid.

The error codes are:

Table 40-34. EMODT Return Value in RAX

Error Code (see Table 40-4) Description
No Error EMODT successful.
SGX_PAGE_NOT_MODIFIABLE The EPC page cannot be modified because it is in the PENDING or MODIFIED state.
SGX_EPC_PAGE_CONFLICT Page is being written by EADD, EAUG, ECREATE, ELDU/B, EMODPR, or EWB.

Concurrency Restrictions

Table 40-35. Base Concurrency Restrictions of EMODT

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

Vol. 3D 40-59 SGX INSTRUCTION REFERENCES

Table 40-36. Additional Concurrency Restrictions of EMODT

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
EMODT Target [DS:RCX] Exclusive SGX_EPC_PAGE _CONFLICT Concurrent Concurrent

Operation

Temp Variables in EMODT 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_SECS</td>
		<td>Effective Address</td>
		<td>32/64</td>
		<td>Physical address of SECS to which EPC operand belongs.</td>
	</tr>
	<tr>
		<td>SCRATCH_SECINFO</td>
		<td>SECINFO</td>
		<td>512</td>
		<td>Scratch storage for holding the contents of DS:RBX.</td>
	</tr>
</table>

IF (DS:RBX is not 64Byte Aligned)
    THEN #GP(0); FI;
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;
SCRATCH_SECINFO ← DS:RBX;
(* Check for misconfigured SECINFO flags*)
IF ( (SCRATCH_SECINFO reserved fields are not zero ) or
    !(SCRATCH_SECINFO.FLAGS.PT is PT_TCS or SCRATCH_SECINFO.FLAGS.PT is PT_TRIM) )
    THEN #GP(0); FI;
(* Check concurrency with SGX1 instructions on the EPC page *)
IF (other SGX1 instructions accessing EPC page) 
    THEN
        RFLAGS.ZF ← 1;
        RAX ← SGX_EPC_PAGE_CONFLICT;
        GOTO DONE;
FI;
IF (EPCM(DS:RCX).VALID is 0)
    THEN #PF(DS:RCX); FI;
(* Check the EPC page for concurrency *)
IF (EPC page in use by another SGX2 instruction) 
    THEN
        RFLAGS.ZF ← 1;
        RAX ← SGX_EPC_PAGE_CONFLICT;
        GOTO DONE;
40-60 Vol. 3D
                            SGX INSTRUCTION REFERENCES
FI;
IF (!(EPCM(DS:RCX).PT is PT_REG or
    (EPCM(DS:RCX).PT is PT_TCS and SCRATCH_SECINFO.FLAGS.PT is PT_TRIM)))
        THEN #PF(DS:RCX); FI;
IF (EPCM(DS:RCX).PENDING is not 0 or (EPCM(DS:RCX).MODIFIED is not 0) )
    THEN 
        RFLAGS.ZF ← 1;
        RAX ← SGX_PAGE_NOT_MODIFIABLE;
        GOTO DONE;
FI;
TMP_SECS ← GET_SECS_ADDRESS
IF (TMP_SECS.ATTRIBUTES.INIT = 0)
    THEN #GP(0); FI;
(* Update EPCM fields *)
EPCM(DS:RCX).PR ← 0;
EPCM(DS:RCX).MODIFIED ← 1;
EPCM(DS:RCX).R ← 0;
EPCM(DS:RCX).W ← 0;
EPCM(DS:RCX).X ← 0;
EPCM(DS:RCX).PT ← SCRATCH_SECINFO.FLAGS.PT;
RFLAGS.ZF ← 0;
RAX ← 0;
DONE:
RFLAGS.CF,PF,AF,OF,SF ← 0;

Flags Affected

Sets ZF if page is not modifiable or if other SGX2 instructions are executing concurrently, otherwise cleared. Clears CF, 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 a memory operand is locked.

#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 a memory operand is locked.

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

Vol. 3D 40-61

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

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