#retbleed — Public Fediverse posts

Some highlights from a x86 core updates merge for #Linux #kernel 6.2:
https://git.kernel.org/torvalds/c/94a855111ed9106971ca2617c5d075269e6aefde #LinuxKernel

```
- Add the call depth tracking mitigation for #Retbleed […] It is a lighterweight software-only fix for Skylake-based cores where enabling IBRS is a big hammer and causes a significant performance impact. [Benchmarks: https://lore.kernel.org/all/2022091511[email protected]/ ]

- Implement a new control flow integrity scheme called FineIBT which is based on the software kCFI implementation […]
```

Call Depth Tracking Coming To #Linux 6.2 To Help Recover Performance On #Intel #Skylake-Era CPUs

-- Much less costly than IBRS in light of #Retbleed. Benchmarks coming.

https://www.phoronix.com/news/Call-Depth-Tracking-Linux-6.2

Original tweet : https://twitter.com/phoronix/status/1602984970838052865

Call Depth Tracking For Less Costly #Retbleed Mitigation Hopes To Land Soon

https://www.phoronix.com/news/Call-Depth-Tracking-Hope-Soon

Original tweet : https://twitter.com/phoronix/status/1571093772280397826

#VMware engineers have tested the #Linux kernel's fix for the #Retbleed speculative execution bug, and report it can impact compute performance by a whopping 70 percent.

Source
https://lkml.iu.edu/hypermail/linux/kernel/2209.1/02248.html

Kernel 6.0 progression
https://lkml.iu.edu/hypermail/linux/kernel/2209.1/03956.html

#VMware: ESXi VM Performance Tanks Up To 70% Due To #Intel #Retbleed Mitigation

https://www.phoronix.com/news/VMware-Linux-5.19-ESXi-Retbleed

Original tweet : https://twitter.com/phoronix/status/1568257842842411010

#Linux #Retbleed overhyped - No fix in sight because attack scenario does not exists

Discussions
https://lore.kernel.org/lkml/CA+G9fYv0[email protected]/

https://lore.kernel.org/lkml/Ys%2FbWIk[email protected]/

#Linux already fixed the #Retbleed #security flaw with Kernel 5.19 RC 7

Torvalds note
https://lkml.iu.edu/hypermail/linux/kernel/2207.2/00816.html

»The #Retbleed mitigations are some of the most performance-wrenching mitigations I've seen in a few years going back to the early Spectre/Meltdown days.«

https://www.phoronix.com/scan.php?page=article&item=retbleed-benchmark&num=1

https://www.phoronix.com/scan.php?page=news_item&px=Retbleed-Ryzen-7-4800U

when will we stop using x86. like at all. like anywhere.

#retbleed

Some of the #retbleed fixes are *very* cisc/x86 - an instruction decoded two ways by jumping back into itself as a way to confuse the branch predictor:
@pro

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a149180fbcf336e97ce4eb2cdc13672727feb94d

#Retbleed benchmarked, it looks bad - for older CPU generations

https://www.phoronix.com/scan.php?page=article&item=retbleed-benchmark&num=1

Ouch... And we get one more. #retbleed is a new kind of Branch Target Injection attack. Update and protect yourself (if at the expense of ~10 to ~30 % performance hit)

https://comsec.ethz.ch/research/microarch/retbleed/

#infosec

#Retbleed: Arbitrary Speculative Code Execution with Return Instructions

https://www.youtube.com/watch?v=dmSPvJxPm80

https://comsec.ethz.ch/research/microarch/retbleed/