IBRS não ativado

Question

No meu computador com o Ubuntu 16.04, o "specter-meltdown-checker" fornece esta saída:

Spectre and Meltdown mitigation detection tool v0.37+

Checking for vulnerabilities on current system
Kernel is Linux 4.4.0-122-generic #146-Ubuntu SMP Mon Apr 23 15:34:04 UTC 2018 x86_64
CPU is Intel(R) Celeron(R) CPU  N3150  @ 1.60GHz

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)
  * 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 (RDCL_NO):  NO 
  * CPU microcode is known to cause stability problems:  NO  (model 76 stepping 3 ucode 0x367 cpuid 0x406c3)
* CPU vulnerability to the three speculative execution attack variants
  * Vulnerable to Variant 1:  YES 
  * Vulnerable to Variant 2:  YES 
  * Vulnerable to Variant 3:  YES 

CVE-2017-5753 [bounds check bypass] aka 'Spectre Variant 1'
* Mitigated according to the /sys interface:  YES  (Mitigation: OSB (observable speculation barrier, Intel v6))
* Kernel has array_index_mask_nospec (x86):  NO 
* Kernel has the Red Hat/Ubuntu patch:  YES 
* Kernel has mask_nospec64 (arm):  NO 
> STATUS:  NOT VULNERABLE  (Mitigation: OSB (observable speculation barrier, Intel v6))

CVE-2017-5715 [branch target injection] aka 'Spectre Variant 2'
* Mitigated according to the /sys interface:  YES  (Mitigation: Full generic retpoline, IBPB (Intel v4))
* Mitigation 1
  * Kernel is compiled with IBRS support:  YES 
    * IBRS enabled and active:  YES  (for both kernel and user space)
  * 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 [rogue data cache load] aka 'Meltdown' aka 'Variant 3'
* 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:  NO  (PCID/INVPCID not supported, performance impact of PTI will be significant)
* Running as a Xen PV DomU:  NO 
> STATUS:  NOT VULNERABLE  (Mitigation: PTI)

A false sense of security is worse than no security at all, see --disclaimer

A atualização do microcódigo suporta o IBRS, mas não está ativada por padrão (mas pode ser ativada, veja a resposta). Em vez disso, a retpolina com IBPB é usada para mitigação. Por que é tão? O IBRS não seria uma proteção melhor como a retpolina, porque o IBRS também protege o espaço do usuário? Como posso forçar o kernel a usar o IBRS?

    

Answer 1

Veja o wiki spectreAndMeltdown / MitigationControls sobre este assunto

No tempo de execução:

echo 0 > /proc/sys/kernel/ibrs_enabled 

desativará o IBRS

echo 1 > /proc/sys/kernel/ibrs_enabled 

ligará o IBRS no kernel

echo 2 > /proc/sys/kernel/ibrs_enabled 

ativará o IBRS no espaço do usuário e no kernel.

Para inspecionar o uso da mudança

sysctl -a|grep ibrs

Tudo feito depois de fazer sudo -i e não usar sudo normal.

Em seguida, verifique se sua ferramenta de relatórios está atualizada.

Mas por que fazer alguma coisa? A mídia está fora de proporção e precisa estar muito mais errada com seu sistema para que alguém possa abusar disso. O senso comum deve prevalecer sobre a paranóia.