Impact: Kernel & all software

Mitigation: recompile software and kernel with a modified compiler that introduces the LFENCE opcode at the proper positions in the resulting code

Performance impact of the mitigation: negligible





Impact: Kernel

Mitigation 1: new opcode via microcode update that should be used by up to date compilers to protect the BTB (by flushing indirect branch predictors)

Mitigation 2: introducing "retpoline" into compilers, and recompile software/OS with it

Performance impact of the mitigation: high for mitigation 1, medium for mitigation 2, depending on your CPU





Impact: Kernel

Mitigation: updated kernel (with PTI/KPTI patches), updating the kernel is enough

Performance impact of the mitigation: low to medium

$ sudo ./spectre-meltdown-checker.sh Spectre and Meltdown mitigation detection tool v0.09 CVE-2017-5753 [bounds check bypass] aka 'Spectre Variant 1' * Kernel compiled with LFENCE opcode inserted at the proper places: NO (only 38 opcodes found, should be >= 60) > STATUS: VULNERABLE CVE-2017-5715 [branch target injection] aka 'Spectre Variant 2' * Mitigation 1 * Hardware (CPU microcode) support for mitigation: NO * Kernel support for IBRS: NO * IBRS enabled for Kernel space: NO * IBRS enabled for User space: NO * Mitigation 2 * Kernel compiled with retpolines: NO > STATUS: VULNERABLE (IBRS hardware + kernel support OR kernel with retpolines are needed to mitigate the vulnerability) CVE-2017-5754 [rogue data cache load] aka 'Meltdown' aka 'Variant 3' * Kernel supports Page Table Isolation (PTI): YES * PTI enabled and active: YES > STATUS: NOT VULNERABLE (PTI mitigates the vulnerability)

A simple shell script to tell if your Linux installation is vulnerable against the 3 "speculative execution" CVEs:Example of the output of the script: