GETSEC[CAPABILITIES] - Report the SMX Capabilities

Opcode

Instruction

Description

NP 0F 37

(EAX = 0)

GETSEC[CAPABILITIES]

Report the SMX capabilities.

The capabilities index is input in EBX with the result returned in EAX.

Description

The GETSEC[CAPABILITIES] function returns a bit vector of supported GETSEC leaf functions. The CAPABILITIES leaf of GETSEC is selected with EAX set to 0 at entry. EBX is used as the selector for returning the bit vector field in EAX. GETSEC[CAPABILITIES] may be executed at all privilege levels, but the CR4.SMXE bit must be set or an unde- fined opcode exception (#UD) is returned.

With EBX = 0 upon execution of GETSEC[CAPABILITIES], EAX returns the a bit vector representing status on the

presence of a Intel® TXT-capable chipset and the first 30 available GETSEC leaf functions. The format of the returned bit vector is provided in Table 7-3.

If bit 0 is set to 1, then an Intel® TXT-capable chipset has been sampled present by the processor. If bits in the range of 1-30 are set, then the corresponding GETSEC leaf function is available. If the bit value at a given bit index is 0, then the GETSEC leaf function corresponding to that index is unsupported and attempted execution results in a #UD.

Bit 31 of EAX indicates if further leaf indexes are supported. If the Extended Leafs bit 31 is set, then additional leaf functions are accessed by repeating GETSEC[CAPABILITIES] with EBX incremented by one. When the most signifi- cant bit of EAX is not set, then additional GETSEC leaf functions are not supported; indexing EBX to a higher value results in EAX returning zero.

Table 7-3. GETSEC Capability Result Encoding (EBX = 0)

Field

Bit position

Description

Chipset Present

0

Intel® TXT-capable chipset is present.

Undefined

1

Reserved

ENTERACCS

2

GETSEC[ENTERACCS] is available.

EXITAC

3

GETSEC[EXITAC] is available.

SENTER

4

GETSEC[SENTER] is available.

SEXIT

5

GETSEC[SEXIT] is available.

PARAMETERS

6

GETSEC[PARAMETERS] is available.

SMCTRL

7

GETSEC[SMCTRL] is available.

WAKEUP

8

GETSEC[WAKEUP] is available.

Undefined

30:9

Reserved

Extended Leafs

31

Reserved for extended information reporting of GETSEC capabilities.

Operation 

IF (CR4.SMXE=0)
   THEN #UD;
ELSIF (in VMX non-root operation)
   THEN VM Exit (reason="GETSEC instruction");
IF (EBX=0) THEN
       BitVector := 0;
       IF (TXT chipset present)
            BitVector[Chipset present] := 1;
       IF (ENTERACCS Available)
            THEN BitVector[ENTERACCS] := 1;
       IF (EXITAC Available)
            THEN BitVector[EXITAC] := 1;
       IF (SENTER Available)
            THEN BitVector[SENTER] := 1;
       IF (SEXIT Available)
            THEN BitVector[SEXIT] := 1;
       IF (PARAMETERS Available)
            THEN BitVector[PARAMETERS] := 1;
       IF (SMCTRL Available)
            THEN BitVector[SMCTRL] := 1;
       IF (WAKEUP Available)
            THEN BitVector[WAKEUP] := 1;
       EAX := BitVector;
ELSE
   EAX := 0;
END;;

Flags Affected

None.

Use of Prefixes

LOCK

Causes #UD.

REP*

Cause #UD (includes REPNE/REPNZ and REP/REPE/REPZ).

Operand size

Causes #UD.

NP

66/F2/F3 prefixes are not allowed.

Segment overrides

Ignored.

Address size

Ignored.

REX

Ignored.

Protected Mode Exceptions

#UD

If CR4.SMXE = 0.

Real-Address Mode Exceptions

#UD

If CR4.SMXE = 0.

Virtual-8086 Mode Exceptions

#UD

If CR4.SMXE = 0.

Compatibility Mode Exceptions

#UD

If CR4.SMXE = 0.

64-Bit Mode Exceptions

#UD

If CR4.SMXE = 0.

VM-exit Condition

Reason (GETSEC)

If in VMX non-root operation.