image/svg+xml SETSSBSY—Mark Shadow Stack Busy Instruction Operand Encoding Description The SETSSBSY instruction verifies the presence of a non-busy supervisor shadow stack token at the address in the IA32_PL0_SSP MSR and marks it busy. Following successful execution of the instruction, the SSP is set to the value of the IA32_PL0_SSP MSR. Operation IF (CR4.CET = 0) THEN #UD; FI; IF (IA32_S_CET.SH_STK_EN = 0) THEN #UD; FI; IF CPL > 0 THEN GP(0); FI; SSP_LA = IA32_PL0_SSP If SSP_LA not aligned to 8 bytes THEN #GP(0); FI; expected_token_value = SSP_LA (* busy bit must not be set *) new_token_value = SSP_LA | BUSY_BIT(* set busy bit; bit position 0 *) IF shadow_stack_lock_cmpxchg8B(SSP_LA, new_token_value, expected_token_value) != expected_token_value THEN #CP(SETSSBSY); FI; SSP = SSP_LA Flags Affected None. C/C ++ Compiler Intrinsic Equivalent SETSSBSYvoid _setssbsy(void); Protected Mode Exceptions #UDIf the LOCK prefix is used. If CR4.CET = 0. IF IA32_S_CET.SH_STK_EN = 0. #GP(0)If IA32_PL0_SSP not aligned to 8 bytes. If CPL is not 0. #CP(setssbsy)If busy bit in token is set. If in 32-bit or compatibility mode, and the address in token is not below 4G. #PF(fault-code)If a page fault occurs. Opcode/ Instruction Op/ En 64/32 bit Mode Support CPUID Feature Flag Description F3 0F 01 E8 SETSSBSY ZOV/VCET_SSSet busy flag in supervisor shadow stack token reference by IA32_PL0_SSP. Op/EnOperand 1Operand 2Operand 3Operand 4 ZONANANANA image/svg+xml Real-Address Mode Exceptions #UDThe SETSSBSY instruction is not recognized in real-address mode. Virtual-8086 Mode Exceptions #UDThe SETSSBSY instruction is not recognized in virtual-8086 mode. Compatibility Mode Exceptions Same as protected mode exceptions. 64-Bit Mode Exceptions Same as protected mode exceptions. This UNOFFICIAL reference was generated from the official Intel® 64 and IA-32 Architectures Software Developer’s Manual by a dumb script. There is no guarantee that some parts aren't mangled or broken and is distributed WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE .