37-6 Vol. 3D

INTRODUCTION TO INTEL® SOFTWARE GUARD EXTENSIONS

On processors that support Intel SGX1 and SGX2, CPUID leaf 12H sub-leaf 2 report physical memory resources 
available for use with Intel SGX. These physical memory sections are typically allocated by BIOS as Processor 
Reserved Memory, and available to the OS to manage as EPC. 
To enumerate how many EPC sections are available to the EPC manager, software can enumerate CPUID leaf 12H 
with sub-leaf index starting from 2, and decode the sub-leaf-type encoding (returned in EAX[3:0]) until the sub-
leaf type is invalid. All invalid sub-leaves of CPUID leaf 12H return EAX/EBX/ECX/EDX with 0.

ECX

31:0

Report the valid bits of SECS.ATTRIBUTES[95:64] that software can set with ECREATE. 

SECS.ATTRIBUTES[n+64] can be set to 1 using ECREATE only if ECX[n] is 1, where n < 32.

EDX

31:0

Report the valid bits of SECS.ATTRIBUTES[127:96] that software can set with ECREATE. 

SECS.ATTRIBUTES[n+96] can be set to 1 using ECREATE only if EDX[n] is 1, where n < 32.

Table 37-6.  CPUID Leaf 12H, Sub-Leaf Index 2 or Higher Enumeration of Intel® SGX Resources

CPUID.(EAX=12H,ECX > 1)

Description Behavior

Register

Bits

EAX

3:0

0000b: This sub-leaf is invalid; EDX:ECX:EBX:EAX return 0.
0001b: This sub-leaf enumerates an EPC section. EBX:EAX and EDX:ECX provide information on the 

Enclave Page Cache (EPC) section.
All other encoding are reserved.

11:4

Reserved (enumerate 0).

31:12

If EAX[3:0] = 0001b, these are bits 31:12 of the physical address of the base of the EPC section.

EBX

19:0

If EAX[3:0] = 0001b, these are bits 51:32 of the physical address of the base of the EPC section.

31:20

Reserved.

ECX

3: 0

If EAX[3:0] 0000b, then all bits of the EDX:ECX pair are enumerated as 0.
If EAX[3:0] 0001b, then this section has confidentiality and integrity protection.
All other encoding are reserved.

11:4

Reserved (enumerate 0).

31:12

If EAX[3:0] = 0001b, these are bits 31:12 of the size of the corresponding EPC section within the 

Processor Reserved Memory.

EDX

19: 0

If EAX[3:0] = 0001b, these are bits 51:32 of the size of the corresponding EPC section within the 

Processor Reserved Memory.

31:20

Reserved.

Table 37-5.  CPUID Leaf 12H, Sub-Leaf 1 Enumeration of Intel® SGX Capabilities

CPUID.(EAX=12H,ECX=1)

Description Behavior

Register

Bits