Module spectre 

Retpoline / Spectre Mitigations

Provides software and hardware mitigations for Spectre-class speculative execution vulnerabilities.

Spectre v1 (Bounds Check Bypass)

• bounds_mask: branchless index clamping that produces a safe index even under mis-speculation.
• speculation_barrier: serialising instruction that halts speculative execution past this point.

Spectre v2 (Branch Target Injection)

• IBRS (Indirect Branch Restricted Speculation): restricts speculative targets of indirect branches to a curated set.
• IBPB (Indirect Branch Prediction Barrier): flushes the Branch Target Buffer on context switches.
• STIBP (Single Thread Indirect Branch Predictors): prevents cross-SMT branch-target poisoning.
• Retpoline: compiler-based mitigation that replaces indirect calls with a construct that never speculatively follows the real target.

Architecture Support

• x86_64: IBRS/IBPB/STIBP via IA32_SPEC_CTRL (MSR 0x48) and IA32_PRED_CMD (MSR 0x49). Feature detection through CPUID leaf 7.
• AArch64: CSV2 (Cache Speculation Variant 2) detection via ID_AA64PFR0_EL1. Barriers via DSB SY + ISB.
• RISC-V: FENCE.I as speculation barrier.

Constants

RETPOLINE_ENABLED

Whether retpoline (compiler-level Spectre v2 mitigation) is active.

Functions

bounds_mask

Branchless bounds mask for Spectre v1 mitigation.

enable_ibrs

Enable IBRS (Indirect Branch Restricted Speculation).

enable_stibp

Enable STIBP (Single Thread Indirect Branch Predictors).

flush_btb

Flush the Branch Target Buffer (issue IBPB).

has_ibpb

Returns true if IBPB is supported by the CPU.

has_ibrs

Returns true if IBRS is supported by the CPU.

has_stibp

Returns true if STIBP is supported by the CPU.

init

Detect and enable Spectre mitigations.

is_hw_mitigated

Returns true if the CPU has hardware-level Spectre mitigations.

is_ibrs_enabled

Returns true if IBRS is currently enabled.

safe_index

Safe array index that clamps to zero under mis-speculation.

speculation_barrier

Insert a full speculation barrier.