Check Spectre and Meltdown Vulnerabilities — The Easy Way
9 min readMay 9, 2022
Sometimes we need to quickly check whether a Linux environment is vulnerable to flaws exploited by known versions of Specter and Meltdown exploits. In practice we have 2 ways to check this: manually or automatically. This article will cover the second way.
Kernel Vulnerabilities
As any system, Linux can be affected by a variety of vulnerabilities. Everyday researchers discover new flaws on many systems. Some of them can lead to serious data loss.
To know more about Linux Kernel vulnerabilities from 1999 to 2022, check this CVE list.
Spectre and Meltdown
Meltdown allows malicious programs to gain access to higher-privileged parts of a computer’s memory, while Spectre steals data from the memory of other applications running on a machine. Meltdown is said to be limited to Intel processors, but Spectre has been exploited on ARM as well as AMD processors.
Meltdown
Meltdown is a hardware vulnerability affecting Intel x86 microprocessors, IBM POWER processors, and some ARM-based microprocessors. It allows a rogue process to read all memory, even when it is not authorized to do so.
To know more about Meltdown vulnerability, click here.
Spectre
Spectre is a class of security vulnerabilities that affects modern microprocessors that perform branch prediction and other forms of speculation. On most processors, the speculative execution resulting from a branch misprediction may leave observable side effects that may reveal private data to attackers. For example, if the pattern of memory accesses performed by such speculative execution depends on private data, the resulting state of the data cache constitutes a side channel through which an attacker may be able to extract information about the private data using a timing attack.
To know more about Spectre vulnerability, click here.
Checking if your System is Vulnerable
So, how can you check if your system is vulnerable?
A nice user provided a script called “spectre-meltdown-checker” for this task. You can clone it with the following command:
# git clone https://github.com/speed47/spectre-meltdown-checker.git
To run the script, execute the command below.
# ./spectre-meltdown-checker.sh 2> /dev/nullThe script will show a nice report. As for an example:
[root@rhv spectre-meltdown-checker]# ./spectre-meltdown-checker.sh 2> /dev/null
Spectre and Meltdown mitigation detection tool v0.44-15-ga485c78
Checking for vulnerabilities on current system
Kernel is Linux 4.18.0-348.7.1.el8_5.x86_64 #1 SMP Wed Dec 8 21:51:17 EST 2021 x86_64
CPU is Intel(R) Xeon(R) CPU E5-2670 v3 @ 2.30GHz
Hardware check
* Hardware support (CPU microcode) for mitigation techniques
* Indirect Branch Restricted Speculation (IBRS)
* SPEC_CTRL MSR is available: YES
* CPU indicates IBRS capability: YES (SPEC_CTRL feature bit)
* Indirect Branch Prediction Barrier (IBPB)
* PRED_CMD MSR is available: YES
* CPU indicates IBPB capability: YES (SPEC_CTRL feature bit)
* Single Thread Indirect Branch Predictors (STIBP)
* SPEC_CTRL MSR is available: YES
* CPU indicates STIBP capability: YES (Intel STIBP feature bit)
* Speculative Store Bypass Disable (SSBD)
* CPU indicates SSBD capability: YES (Intel SSBD)
* L1 data cache invalidation
* FLUSH_CMD MSR is available: YES
* CPU indicates L1D flush capability: YES (L1D flush feature bit)
* Microarchitectural Data Sampling
* VERW instruction is available: YES (MD_CLEAR feature bit)
* Enhanced IBRS (IBRS_ALL)
* CPU indicates ARCH_CAPABILITIES MSR availability: NO
* ARCH_CAPABILITIES MSR advertises IBRS_ALL capability: NO
* CPU explicitly indicates not being vulnerable to Meltdown/L1TF (RDCL_NO): NO
* CPU explicitly indicates not being vulnerable to Variant 4 (SSB_NO): NO
* CPU/Hypervisor indicates L1D flushing is not necessary on this system: NO
* Hypervisor indicates host CPU might be vulnerable to RSB underflow (RSBA): NO
* CPU explicitly indicates not being vulnerable to Microarchitectural Data Sampling (MDS_NO): NO
* CPU explicitly indicates not being vulnerable to TSX Asynchronous Abort (TAA_NO): NO
* CPU explicitly indicates not being vulnerable to iTLB Multihit (PSCHANGE_MSC_NO): NO
* CPU explicitly indicates having MSR for TSX control (TSX_CTRL_MSR): NO
* CPU supports Transactional Synchronization Extensions (TSX): NO
* CPU supports Software Guard Extensions (SGX): NO
* CPU supports Special Register Buffer Data Sampling (SRBDS): NO
* CPU microcode is known to cause stability problems: NO (family 0x6 model 0x3f stepping 0x2 ucode 0x46 cpuid 0x306f2)
* CPU microcode is the latest known available version: YES (latest version is 0x44 dated 2020/05/27 according to builtin firmwares DB v191+i20210217)
* CPU vulnerability to the speculative execution attack variants
* Affected by CVE-2017-5753 (Spectre Variant 1, bounds check bypass): YES
* Affected by CVE-2017-5715 (Spectre Variant 2, branch target injection): YES
* Affected by CVE-2017-5754 (Variant 3, Meltdown, rogue data cache load): YES
* Affected by CVE-2018-3640 (Variant 3a, rogue system register read): YES
* Affected by CVE-2018-3639 (Variant 4, speculative store bypass): YES
* Affected by CVE-2018-3615 (Foreshadow (SGX), L1 terminal fault): NO
* Affected by CVE-2018-3620 (Foreshadow-NG (OS), L1 terminal fault): YES
* Affected by CVE-2018-3646 (Foreshadow-NG (VMM), L1 terminal fault): YES
* Affected by CVE-2018-12126 (Fallout, microarchitectural store buffer data sampling (MSBDS)): YES
* Affected by CVE-2018-12130 (ZombieLoad, microarchitectural fill buffer data sampling (MFBDS)): YES
* Affected by CVE-2018-12127 (RIDL, microarchitectural load port data sampling (MLPDS)): YES
* Affected by CVE-2019-11091 (RIDL, microarchitectural data sampling uncacheable memory (MDSUM)): YES
* Affected by CVE-2019-11135 (ZombieLoad V2, TSX Asynchronous Abort (TAA)): NO
* Affected by CVE-2018-12207 (No eXcuses, iTLB Multihit, machine check exception on page size changes (MCEPSC)): YES
* Affected by CVE-2020-0543 (Special Register Buffer Data Sampling (SRBDS)): NO
CVE-2017-5753 aka 'Spectre Variant 1, bounds check bypass'
* Mitigated according to the /sys interface: YES (Mitigation: usercopy/swapgs barriers and __user pointer sanitization)
* Kernel has array_index_mask_nospec: YES (1 occurrence(s) found of x86 64 bits array_index_mask_nospec())
* Kernel has the Red Hat/Ubuntu patch: NO
* Kernel has mask_nospec64 (arm64): NO
* Kernel has array_index_nospec (arm64): NO
> STATUS: NOT VULNERABLE (Mitigation: usercopy/swapgs barriers and __user pointer sanitization)
CVE-2017-5715 aka 'Spectre Variant 2, branch target injection'
* Mitigated according to the /sys interface: YES (Mitigation: Full generic retpoline, IBPB: conditional, IBRS_FW, STIBP: conditional, RSB filling)
* Mitigation 1
* Kernel is compiled with IBRS support: YES
* IBRS enabled and active: YES (for firmware code only)
* Kernel is compiled with IBPB support: YES
* IBPB enabled and active: YES
* Mitigation 2
* Kernel has branch predictor hardening (arm): NO
* Kernel compiled with retpoline option: YES
* Kernel compiled with a retpoline-aware compiler: YES (kernel reports full retpoline compilation)
> STATUS: NOT VULNERABLE (Full retpoline + IBPB are mitigating the vulnerability)
CVE-2017-5754 aka 'Variant 3, Meltdown, rogue data cache load'
* Mitigated according to the /sys interface: YES (Mitigation: PTI)
* Kernel supports Page Table Isolation (PTI): YES
* PTI enabled and active: YES
* Reduced performance impact of PTI: YES (CPU supports INVPCID, performance impact of PTI will be greatly reduced)
* Running as a Xen PV DomU: NO
> STATUS: NOT VULNERABLE (Mitigation: PTI)
CVE-2018-3640 aka 'Variant 3a, rogue system register read'
* CPU microcode mitigates the vulnerability: YES
> STATUS: NOT VULNERABLE (your CPU microcode mitigates the vulnerability)
CVE-2018-3639 aka 'Variant 4, speculative store bypass'
* Mitigated according to the /sys interface: YES (Mitigation: Speculative Store Bypass disabled via prctl and seccomp)
* Kernel supports disabling speculative store bypass (SSB): YES (found in /proc/self/status)
* SSB mitigation is enabled and active: YES (per-thread through prctl)
* SSB mitigation currently active for selected processes: YES (auditd qemu-kvm systemd-journald systemd-logind systemd-machined systemd-resolved systemd-udevd)
> STATUS: NOT VULNERABLE (Mitigation: Speculative Store Bypass disabled via prctl and seccomp)
CVE-2018-3615 aka 'Foreshadow (SGX), L1 terminal fault'
* CPU microcode mitigates the vulnerability: N/A
> STATUS: NOT VULNERABLE (your CPU vendor reported your CPU model as not vulnerable)
CVE-2018-3620 aka 'Foreshadow-NG (OS), L1 terminal fault'
* Mitigated according to the /sys interface: YES (Mitigation: PTE Inversion; VMX: conditional cache flushes, SMT vulnerable)
* Kernel supports PTE inversion: YES (found in kernel image)
* PTE inversion enabled and active: YES
> STATUS: NOT VULNERABLE (Mitigation: PTE Inversion; VMX: conditional cache flushes, SMT vulnerable)
CVE-2018-3646 aka 'Foreshadow-NG (VMM), L1 terminal fault'
* Information from the /sys interface: Mitigation: PTE Inversion; VMX: conditional cache flushes, SMT vulnerable
* This system is a host running a hypervisor: NO
* Mitigation 1 (KVM)
* EPT is disabled: NO
* Mitigation 2
* L1D flush is supported by kernel: YES (found flush_l1d in /proc/cpuinfo)
* L1D flush enabled: YES (conditional flushes)
* Hardware-backed L1D flush supported: YES (performance impact of the mitigation will be greatly reduced)
* Hyper-Threading (SMT) is enabled: YES
> STATUS: NOT VULNERABLE (this system is not running a hypervisor)
CVE-2018-12126 aka 'Fallout, microarchitectural store buffer data sampling (MSBDS)'
* Mitigated according to the /sys interface: YES (Mitigation: Clear CPU buffers; SMT vulnerable)
* Kernel supports using MD_CLEAR mitigation: YES (md_clear found in /proc/cpuinfo)
* Kernel mitigation is enabled and active: YES
* SMT is either mitigated or disabled: NO
> STATUS: NOT VULNERABLE (Your microcode and kernel are both up to date for this mitigation, and mitigation is enabled)
CVE-2018-12130 aka 'ZombieLoad, microarchitectural fill buffer data sampling (MFBDS)'
* Mitigated according to the /sys interface: YES (Mitigation: Clear CPU buffers; SMT vulnerable)
* Kernel supports using MD_CLEAR mitigation: YES (md_clear found in /proc/cpuinfo)
* Kernel mitigation is enabled and active: YES
* SMT is either mitigated or disabled: NO
> STATUS: NOT VULNERABLE (Your microcode and kernel are both up to date for this mitigation, and mitigation is enabled)
CVE-2018-12127 aka 'RIDL, microarchitectural load port data sampling (MLPDS)'
* Mitigated according to the /sys interface: YES (Mitigation: Clear CPU buffers; SMT vulnerable)
* Kernel supports using MD_CLEAR mitigation: YES (md_clear found in /proc/cpuinfo)
* Kernel mitigation is enabled and active: YES
* SMT is either mitigated or disabled: NO
> STATUS: NOT VULNERABLE (Your microcode and kernel are both up to date for this mitigation, and mitigation is enabled)
CVE-2019-11091 aka 'RIDL, microarchitectural data sampling uncacheable memory (MDSUM)'
* Mitigated according to the /sys interface: YES (Mitigation: Clear CPU buffers; SMT vulnerable)
* Kernel supports using MD_CLEAR mitigation: YES (md_clear found in /proc/cpuinfo)
* Kernel mitigation is enabled and active: YES
* SMT is either mitigated or disabled: NO
> STATUS: NOT VULNERABLE (Your microcode and kernel are both up to date for this mitigation, and mitigation is enabled)
CVE-2019-11135 aka 'ZombieLoad V2, TSX Asynchronous Abort (TAA)'
* Mitigated according to the /sys interface: YES (Not affected)
* TAA mitigation is supported by kernel: YES (found tsx_async_abort in kernel image)
* TAA mitigation enabled and active: NO
> STATUS: NOT VULNERABLE (your CPU vendor reported your CPU model as not vulnerable)
CVE-2018-12207 aka 'No eXcuses, iTLB Multihit, machine check exception on page size changes (MCEPSC)'
* Mitigated according to the /sys interface: YES (KVM: Mitigation: Split huge pages)
* This system is a host running a hypervisor: NO
* iTLB Multihit mitigation is supported by kernel: YES (found itlb_multihit in kernel image)
* iTLB Multihit mitigation enabled and active: YES (KVM: Mitigation: Split huge pages)
> STATUS: NOT VULNERABLE (this system is not running a hypervisor)
CVE-2020-0543 aka 'Special Register Buffer Data Sampling (SRBDS)'
* Mitigated according to the /sys interface: YES (Not affected)
* SRBDS mitigation control is supported by the kernel: YES (found SRBDS implementation evidence in kernel image. Your kernel is up to date for SRBDS mitigation)
* SRBDS mitigation control is enabled and active: NO
> STATUS: NOT VULNERABLE (your CPU vendor reported your CPU model as not vulnerable)
> SUMMARY: CVE-2017-5753:OK CVE-2017-5715:OK CVE-2017-5754:OK CVE-2018-3640:OK CVE-2018-3639:OK CVE-2018-3615:OK CVE-2018-3620:OK CVE-2018-3646:OK CVE-2018-12126:OK CVE-2018-12130:OK CVE-2018-12127:OK CVE-2019-11091:OK CVE-2019-11135:OK CVE-2018-12207:OK CVE-2020-0543:OK
Need more detailed information about mitigation options? Use --explain
A false sense of security is worse than no security at all, see --disclaimer
What to do if you are Vulnerable
Modern Linux Kernels already patched this flow. However, it is necessary to also update the hardware firmware. Each system has It’s own way to update firmwares. I’d recommend to start consulting the manufacture’s manual.
But there is a caveat within theses mitigations. It can cause a performance impact. If your system is behaving slowly after kernel updates, you can try to disable those mitigations (beware of the security issues this may cause).
To know more about disabling mitigations on RHEL, please click here.
That’s it! Have a nice Spectre and Meltdown checking!
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