spectre_v2 module

The module checks if system includes hardware mitigations for Speculative Execution Side Channel. Specifically, it verifies that the system supports CPU mitigations for Branch Target Injection vulnerability a.k.a. Spectre Variant 2 (CVE-2017-5715)

The module checks if the following hardware mitigations are supported by the CPU and enabled by the OS/software:

  1. Indirect Branch Restricted Speculation (IBRS) and Indirect Branch Predictor Barrier (IBPB): CPUID.(EAX=7H,ECX=0):EDX[26] == 1

  2. Single Thread Indirect Branch Predictors (STIBP): CPUID.(EAX=7H,ECX=0):EDX[27] == 1 IA32_SPEC_CTRL[STIBP] == 1


  4. @TODO: Mitigation for Rogue Data Cache Load (RDCL): CPUID.(EAX=7H,ECX=0):EDX[29] == 1 IA32_ARCH_CAPABILITIES[RDCL_NO] == 1

In addition to checking if CPU supports and OS enables all mitigations, we need to check that relevant MSR bits are set consistently on all logical processors (CPU threads).

The module returns the following results:


IBRS/IBPB is not supported


IBRS/IBPB is supported

Enhanced IBRS is not supported


IBRS/IBPB is supported

Enhanced IBRS is supported

Enhanced IBRS is not enabled by the OS


IBRS/IBPB is supported

STIBP is not supported or not enabled by the OS


IBRS/IBPB is supported

Enhanced IBRS is supported

Enhanced IBRS is enabled by the OS

STIBP is supported


  • The module returns WARNING when CPU doesn’t support enhanced IBRS Even though OS/software may use basic IBRS by setting IA32_SPEC_CTRL[IBRS] when necessary, we have no way to verify this

  • The module returns WARNING when CPU supports enhanced IBRS but OS doesn’t set IA32_SPEC_CTRL[IBRS] Under enhanced IBRS, OS can set IA32_SPEC_CTRL[IBRS] once to take advantage of IBRS protection

  • The module returns WARNING when CPU doesn’t support STIBP or OS doesn’t enable it Per Speculative Execution Side Channel Mitigations: “enabling IBRS prevents software operating on one logical processor from controlling the predicted targets of indirect branches executed on another logical processor. For that reason, it is not necessary to enable STIBP when IBRS is enabled”

  • OS/software may implement “retpoline” mitigation for Spectre variant 2 instead of using CPU hardware IBRS/IBPB

@TODO: we should verify CPUID.07H:EDX on all logical CPUs as well because it may differ if ucode update wasn’t loaded on all CPU cores

Hardware registers used:

  • CPUID.(EAX=7H,ECX=0):EDX[26] - enumerates support for IBRS and IBPB

  • CPUID.(EAX=7H,ECX=0):EDX[27] - enumerates support for STIBP

  • CPUID.(EAX=7H,ECX=0):EDX[29] - enumerates support for the IA32_ARCH_CAPABILITIES MSR

  • IA32_ARCH_CAPABILITIES[IBRS_ALL] - enumerates support for enhanced IBRS

  • IA32_ARCH_CAPABILITIES[RCDL_NO] - enumerates support RCDL mitigation

  • IA32_SPEC_CTRL[IBRS] - enable control for enhanced IBRS by the software/OS

  • IA32_SPEC_CTRL[STIBP] - enable control for STIBP by the software/OS