Speculative Store Bypass

Speculative Store Bypass (SSB) (CVE- 2018-3639) is the name given to a hardware security vulnerability and its exploitation that takes advantage of speculative execution in a similar way to the Meltdown and Spectre security vulnerabilities.[1] It affects the ARM, AMD and Intel families of processors. It was discovered by researchers at Microsoft Security Response Center and Google Project Zero (GPZ).[2] After being leaked on May 3, 2018 as part of a group of eight additional Spectre-class flaws provisionally named Spectre-NG,[3][4][5][6] it was first disclosed to the public as "Variant 4" on May 21, 2018, alongside a related speculative execution vulnerability designated "Variant 3a".[7][1]

Details

Speculative execution exploit Variant 4,[8] is referred to as Speculative Store Bypass (SSB),[1][9] and has been assigned CVE-2018-3639.[7] SSB is named Variant 4, but it is the fifth variant in the Spectre-Meltdown class of vulnerabilities.[7]

Steps involved in exploit:[1]

  1. "Slowly" store a value at a memory location
  2. "Quickly" load that value from that memory location
  3. Utilize the value that was just read to disrupt the cache in a detectable way

Impact and mitigation

Intel claims that web browsers that are already patched to mitigate Spectre Variants 1 and 2 are partially protected against Variant 4.[7] Intel said in a statement that the likelihood of end users being affected was "low" and that not all protections would be on by default due to some impact on performance.[10]

Intel is planning to address Variant 4 by releasing a microcode patch that creates a new hardware flag named Speculative Store Bypass Disable (SSBD).[7][2][11] A stable microcode patch is yet to be delivered, with Intel suggesting that the patch will be ready "in the coming weeks".[7] Many operating system vendors will be releasing software updates to assist with mitigating Variant 4;[12][2][13] however, microcode/firmware updates are required for the software updates to have an effect.[12]

Speculative execution exploit variants

Summary of speculative execution variants[14][7][15]
VulnerabilityCVEExploit namePublic vulnerability name
Spectre2017-5753Variant 1Bounds Check Bypass (BCB)
Spectre2017-5715Variant 2Branch Target Injection (BTI)
Meltdown2017-5754Variant 3Rogue Data Cache Load (RDCL)
Spectre-NG2018-3640Variant 3aRogue System Register Read (RSRE)
Spectre-NG2018-3639Variant 4Speculative Store Bypass (SSB)
Spectre-NG2018-3665Lazy FP State Restore
Spectre-NG2018-3693Bounds Check Bypass Store (BCBS)
Foreshadow2018-3615Variant 5L1 Terminal Fault (L1TF)
Foreshadow-NG2018-3620
Foreshadow-NG2018-3646

References

  1. 1 2 3 4 Bright, Peter (2018-05-22). "Predictable problems - New speculative-execution vulnerability strikes AMD, ARM, and Intel". Ars Technica. Archived from the original on 2018-05-26. Retrieved 2018-05-25.
  2. 1 2 3 Ubuntu Community (2018-05-21). "Variant4". Archived from the original on 2018-05-21. Retrieved 2018-05-21.
  3. ↑ Schmidt, Jürgen (2018-05-03). "Super-GAU für Intel: Weitere Spectre-Lücken im Anflug". c't - magazin für computertechnik (in German). Heise online. Archived from the original on 2018-05-05. Retrieved 2018-05-03. Schmidt, Jürgen (2018-05-03). "Exclusive: Spectre-NG - Multiple new Intel CPU flaws revealed, several serious". c't - magazin für computertechnik. Heise online. Archived from the original on 2018-05-05. Retrieved 2018-05-04.
  4. ↑ Fischer, Martin (2018-05-03). "Spectre-NG: Intel-Prozessoren von neuen hochriskanten Sicherheitslücken betroffen, erste Reaktionen von AMD und Intel". c't - magazin für computertechnik (in German). Heise online. Archived from the original on 2018-05-05. Retrieved 2018-05-04.
  5. ↑ Tung, Liam (2018-05-04). "Are 8 new 'Spectre-class' flaws about to be exposed? Intel confirms it's readying fixes". ZDNet. Archived from the original on 2018-05-22. Retrieved 2018-03-04.
  6. ↑ Kumar, Mohit (2018-05-04). "8 New Spectre-Class Vulnerabilities (Spectre-NG) Found in Intel CPUs". The Hacker News. Archived from the original on 2018-05-05. Retrieved 2018-05-05.
  7. 1 2 3 4 5 6 7 "Q2 2018 Speculative Execution Side Channel Update". Intel. 2018-05-21. Archived from the original on 2018-05-21. Retrieved 2018-05-21.
  8. ↑ Warren, Tom (2018-05-21). "Google and Microsoft disclose new CPU flaw, and the fix can slow machines down - New firmware updates are on the way". The Verge. Archived from the original on 2018-05-26. Retrieved 2018-05-22.
  9. ↑ Martindale, Jon (2018-05-22). "New Spectre-like bug could mean more performance-degrading patches". Digital Trends. Archived from the original on 2018-05-26. Retrieved 2018-05-22.
  10. ↑ Newman, Lily Hay (2018-05-21). "After Meltdown and Spectre, Another Scary Chip Flaw Emerges". Wired. Archived from the original on 2018-05-26. Retrieved 2018-05-26.
  11. ↑ "Speculative Execution Side Channel Mitigations" (PDF). Revision 2.0. Intel. May 2018 [January 2018]. Document Number: 336996-002. Retrieved 2018-05-26.
  12. 1 2 "Kernel Side-Channel Attack using Speculative Store Bypass - CVE-2018-3639". RedHat. 2018-05-21. Resolve tab. Archived from the original on 2018-05-21. Retrieved 2018-05-22.
  13. ↑ Miller, Matt. "Analysis and mitigation of speculative store bypass (CVE-2018-3639)". Microsoft Security Response Center. Speculative store bypass disable (SSBD) section. Archived from the original on 2018-05-21. Retrieved 2018-05-21.
  14. ↑ "Vulnerability Note VU#180049 - CPU hardware utilizing speculative execution may be vulnerable to cache side-channel attacks". CERT. 2018-05-24 [2018-05-21]. Archived from the original on 2018-05-26. Retrieved 2018-05-26.
  15. ↑ Windeck, Christof (2018-05-21). "CPU-Sicherheitslücken Spectre-NG: Updates rollen an Update". Heise Security (in German). Archived from the original on 2018-05-21. Retrieved 2018-05-21.
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