EWB — Invalidate an EPC Page and Write out to Main Memory

Instruction Operand Encoding ¶

Description ¶

This leaf function copies a page from the EPC to regular main memory. As part of the copying process, the page is cryptographically protected. This instruction can only be executed when current privilege level is 0.

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

EWB Memory Parameter Semantics ¶

The error codes are:

Concurrency Restrictions ¶

Operation ¶

Temp Variables in EWB Operational Flow ¶

IF ( (DS:RBX is not 32Byte Aligned) or (DS:RCX is not 4KByte Aligned) )

THEN #GP(0); FI;

IF (DS:RCX does not resolve within an EPC)

THEN #PF(DS:RCX); FI;

IF (DS:RDX is not 8Byte Aligned)

THEN #GP(0); FI;

IF (DS:RDX does not resolve within an EPC)

THEN #PF(DS:RDX); FI;

(* EPCPAGE and VASLOT should not resolve to the same EPC page*)

IF (DS:RCX and DS:RDX resolve to the same EPC page)

THEN #GP(0); FI;

TMP_SRCPGE := DS:RBX.SRCPGE;

(* Note PAGEINFO.PCMD is overlaid on top of PAGEINFO.SECINFO *)

TMP_PCMD := DS:RBX.PCMD;

If (DS:RBX.LINADDR ≠ 0) OR (DS:RBX.SECS ≠ 0)

THEN #GP(0); FI;

IF ( (DS:TMP_PCMD is not 128Byte Aligned) or (DS:TMP_SRCPGE is not 4KByte Aligned) )

THEN #GP(0); FI;

(* Check for concurrent Intel SGX instruction access to the page *)

IF (Other Intel SGX instruction is accessing page)

THEN

IF (<<VMX non-root operation>> AND <<ENABLE_EPC_VIRTUALIZATION_EXTENSIONS>>)

THEN

VMCS.Exit_reason := SGX_CONFLICT;

VMCS.Exit_qualification.code := EPC_PAGE_CONFLICT_EXCEPTION;

VMCS.Exit_qualification.error := 0;

VMCS.Guest-physical_address := << translation of DS:RCX produced by paging >>;

VMCS.Guest-linear_address := DS:RCX;

Deliver VMEXIT;

ELSE

#GP(0);

FI;

FI;

(*Check if the VA Page is being removed or changed*)

IF (VA Page is being modified)

THEN #GP(0); FI;

(* Verify that EPCPAGE and VASLOT page are valid EPC pages and DS:RDX is VA *)

IF (EPCM(DS:RCX).VALID = 0)

THEN #PF(DS:RCX); FI;

IF ( (EPCM(DS:RDX & ~0FFFH).VALID = 0) or (EPCM(DS:RDX & ~FFFH).PT is not PT_VA) )

THEN #PF(DS:RDX); FI;

(* Perform page-type-specific exception checks *)

IF ( (EPCM(DS:RCX).PT is PT_REG) or (EPCM(DS:RCX).PT is PT_TCS) or (EPCM(DS:RCX).PT is PT_TRIM ) or

(EPCM(DS:RCX).PT is PT_SS_FIRST ) or (EPCM(DS:RCX).PT is PT_SS_REST))

THEN

TMP_SECS = Obtain SECS through EPCM(DS:RCX)

(* Check that EBLOCK has occurred correctly *)

IF (EBLOCK is not correct)

THEN #GP(0); FI;

FI;

RFLAGS.ZF,CF,PF,AF,OF,SF := 0;

RAX := 0;

(* Zero out TMP_HEADER*)

TMP_HEADER[ sizeof(TMP_HEADER) - 1 : 0] := 0;

(* Perform page-type-specific checks *)

IF ( (EPCM(DS:RCX).PT is PT_REG) or (EPCM(DS:RCX).PT is PT_TCS) or (EPCM(DS:RCX).PT is PT_TRIM )or

(EPCM(DS:RCX).PT is PT_SS_FIRST ) or (EPCM(DS:RCX).PT is PT_SS_REST))

THEN

(* check to see if the page is evictable *)

IF (EPCM(DS:RCX).BLOCKED = 0)

THEN

RAX := SGX_PAGE NOT_BLOCKED;

RFLAGS.ZF := 1;

GOTO ERROR_EXIT;

FI;

(* Check if tracking done correctly *)

IF (Tracking not correct)

THEN

RAX := SGX_NOT_TRACKED;

RFLAGS.ZF := 1;

GOTO ERROR_EXIT;

FI;

(* Obtain EID to establish cryptographic binding between the paged-out page and the enclave *)

TMP_HEADER.EID := TMP_SECS.EID;

(* Obtain EID as an enclave handle for software *)

TMP_PCMD_ENCLAVEID := TMP_SECS.EID;

ELSE IF (EPCM(DS:RCX).PT is PT_SECS)

(*check that there are no child pages inside the enclave *)

IF (DS:RCX has an EPC page associated with it)

THEN

RAX := SGX_CHILD_PRESENT;

RFLAGS.ZF := 1;

GOTO ERROR_EXIT;

FI:

(* treat SECS as having a child page when VIRTCHILDCNT is non-zero *)

IF (<<in VMX non-root operation>> AND

<<ENABLE_EPC_VIRTUALIZATION_EXTENSIONS>> AND

(SECS(DS:RCX).VIRTCHILDCNT ≠ 0))

THEN

RFLAGS.ZF := 1;

RAX := SGX_CHILD_PRESENT;

GOTO ERROR_EXIT;

FI;

TMP_HEADER.EID := 0;

(* Obtain EID as an enclave handle for software *)

TMP_PCMD_ENCLAVEID := (DS:RCX).EID;

ELSE IF (EPCM(DS:RCX).PT is PT_VA)

TMP_HEADER.EID := 0; // Zero is not a special value

(* No enclave handle for VA pages*)

TMP_PCMD_ENCLAVEID := 0;

FI;

TMP_HEADER.LINADDR := EPCM(DS:RCX).ENCLAVEADDRESS;

TMP_HEADER.SECINFO.FLAGS.PT := EPCM(DS:RCX).PT;

TMP_HEADER.SECINFO.FLAGS.RWX := EPCM(DS:RCX).RWX;

TMP_HEADER.SECINFO.FLAGS.PENDING := EPCM(DS:RCX).PENDING;

TMP_HEADER.SECINFO.FLAGS.MODIFIED := EPCM(DS:RCX).MODIFIED;

TMP_HEADER.SECINFO.FLAGS.PR := EPCM(DS:RCX).PR;

(* Encrypt the page, DS:RCX could be encrypted in place. AES-GCM produces 2 values, {ciphertext, MAC}. *)

(* AES-GCM input parameters: key, GCM Counter, MAC_HDR, MAC_HDR_SIZE, SRC, SRC_SIZE)*)

{DS:TMP_SRCPGE, DS:TMP_PCMD.MAC} := AES_GCM_ENC(CR_BASE_PK), (TMP_VER << 32),

TMP_HEADER, 128, DS:RCX, 4096);

(* Write the output *)

Zero out DS:TMP_PCMD.SECINFO

DS:TMP_PCMD.SECINFO.FLAGS.PT := EPCM(DS:RCX).PT;

DS:TMP_PCMD.SECINFO.FLAGS.RWX := EPCM(DS:RCX).RWX;

DS:TMP_PCMD.SECINFO.FLAGS.PENDING := EPCM(DS:RCX).PENDING;

DS:TMP_PCMD.SECINFO.FLAGS.MODIFIED := EPCM(DS:RCX).MODIFIED;

DS:TMP_PCMD.SECINFO.FLAGS.PR := EPCM(DS:RCX).PR;

DS:TMP_PCMD.RESERVED := 0;

DS:TMP_PCMD.ENCLAVEID := TMP_PCMD_ENCLAVEID;

DS:RBX.LINADDR := EPCM(DS:RCX).ENCLAVEADDRESS;

(*Check if version array slot was empty *)

IF ([DS.RDX])

THEN

RAX := SGX_VA_SLOT_OCCUPIED

RFLAGS.CF := 1;

FI;

(* Write version to Version Array slot *)

[DS.RDX] := TMP_VER;

(* Free up EPCM Entry *)

EPCM.(DS:RCX).VALID := 0;

ERROR_EXIT:

Flags Affected ¶

ZF is set if page is not blocked, not tracked, or a child is present. Otherwise cleared.

CF is set if VA slot is previously occupied, Otherwise cleared.

Protected Mode Exceptions ¶

64-Bit Mode Exceptions ¶