INCSSPD/INCSSPQ—Increment Shadow Stack Pointer

Opcode/Instruction	Op /En	64/32 bit Mode Support	CPUID Feature Flag	Description
F3 0F AE /05 INCSSPD r32	R	V/V	CET_SS	Increment SSP by 4 * r32[7:0].
F3 REX.W 0F AE /05 INCSSPQ r64	R	V/N.E.	CET_SS	Increment SSP by 8 * r64[7:0].

Instruction Operand Encoding

Op/En	Tuple Type	Operand 1	Operand 2	Operand 3	Operand 4
R	N/A	ModRM:r/m (r)	N/A	N/A	N/A

Description

This instruction can be used to increment the current shadow stack pointer by the operand size of the instruction times the unsigned 8-bit value specified by bits 7:0 in the source operand. The instruction performs a pop and discard of the first and last element on the shadow stack in the range specified by the unsigned 8-bit value in bits 7:0 of the source operand.

Operation

IF CPL = 3
    IF (CR4.CET & IA32_U_CET.SH_STK_EN) = 0
         THEN #UD; FI;
ELSE
    IF (CR4.CET & IA32_S_CET.SH_STK_EN) = 0
         THEN #UD; FI;
FI;
IF (operand size is 64-bit)
    THEN
         Range := R64[7:0];
         shadow_stack_load 8 bytes from SSP;
         IF Range > 0
              THEN shadow_stack_load 8 bytes from SSP + 8 * (Range - 1);
         FI;
         SSP := SSP + Range * 8;
    ELSE
         Range := R32[7:0];
         shadow_stack_load 4 bytes from SSP;
         IF Range > 0
              THEN shadow_stack_load 4 bytes from SSP + 4 * (Range - 1);
         FI;
         SSP := SSP + Range * 4;
FI;

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent

INCSSPD void _incsspd(int);

INCSSPQ void _incsspq(int);

Protected Mode Exceptions

#UD

If the LOCK prefix is used.

If CR4.CET = 0.

IF CPL = 3 and IA32_U_CET.SH_STK_EN = 0.

IF CPL < 3 and IA32_S_CET.SH_STK_EN = 0.

#PF(fault-code)

If a page fault occurs.

Real-Address Mode Exceptions

#UD	The INCSSP instruction is not recognized in real-address mode.

Virtual-8086 Mode Exceptions

#UD	The INCSSP instruction is not recognized in virtual-8086 mode.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

Same exceptions as in protected mode.