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posted by martyb on Friday June 05 2020, @08:40AM   Printer-friendly
from the help-less,-please dept.

Linus Torvalds rejects 'beyond stupid' AWS-made Linux patch for Intel CPU Snoop attack

Linux kernel head Linus Torvalds has trashed a patch from Amazon Web Services (AWS) engineers that was aimed at mitigating the Snoop attack on Intel CPUs discovered by an AWS engineer earlier this year. [...] AWS engineer Pawel Wieczorkiewicz discovered a way to leak data from an Intel CPU's memory via its L1D cache, which sits in CPU cores, through 'bus snooping' – the cache updating operation that happens when data is modified in L1D.

In the wake of the disclosure, AWS engineer Balbir Singh proposed a patch for the Linux kernel for applications to be able to opt in to flush the L1D cache when a task is switched out. [...] The feature would allow applications on an opt-in basis to call prctl(2) to flush the L1D cache for a task once it leaves the CPU, assuming the hardware supports it.

But, as spotted by Phoronix, Torvalds believes the patch will allow applications that opt in to the patch to degrade CPU performance for other applications.

"Because it looks to me like this basically exports cache flushing instructions to user space, and gives processes a way to just say 'slow down anybody else I schedule with too'," wrote Torvalds yesterday. "In other words, from what I can tell, this takes the crazy 'Intel ships buggy CPU's and it causes problems for virtualization' code (which I didn't much care about), and turns it into 'anybody can opt in to this disease, and now it affects even people and CPU's that don't need it and configurations where it's completely pointless'."

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  • (Score: 5, Insightful) by Thexalon on Friday June 05 2020, @02:53PM (4 children)

    by Thexalon (636) Subscriber Badge on Friday June 05 2020, @02:53PM (#1003761)

    There was a time when we'd periodically get stories that amounted to "WAAAAA! Linus was mean to me!" And the funny thing was that when I looked into the actual discussion in question, every single time Linus was right and the person making the complaint was wrong. I'm sure he has made some mistakes, but he comes across as quite open to technical arguments when he does so.

    If his couple of months of exile taught him how to be nicer about telling someone with a bad patch where to stick it, that's fine, but he's repeatedly demonstrated why he's still the BDFL of Linux despite various efforts to unseat him.

    The only thing that stops a bad guy with a compiler is a good guy with a compiler.
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  • (Score: 0) by Anonymous Coward on Friday June 05 2020, @03:31PM (3 children)

    by Anonymous Coward on Friday June 05 2020, @03:31PM (#1003785)

    This is something that a few $contributions won't solve is it?

    • (Score: 2) by TheReaperD on Friday June 05 2020, @05:13PM (2 children)

      by TheReaperD (5556) on Friday June 05 2020, @05:13PM (#1003840)

      Some big $$$ companies that wanted to hijack the Linux kernel development have tried, but thankfully, the community wasn't buying their bullshit.

      Ad eundum quo nemo ante iit
      • (Score: 3, Funny) by Anonymous Coward on Friday June 05 2020, @09:06PM (1 child)

        by Anonymous Coward on Friday June 05 2020, @09:06PM (#1003957)

        Instead we have the travesty known as systemd, thanks to incompetent buffoons on the Red Hat/IBM payroll. I won't mention any of these motherfucking pieces of shit by name, but one is Lennart Poettering. Yes, I know systemd isn't the kernel for all those pedantic folks.

        Seriously though, remember that time Linus took off work for like 2 weeks or something, then came back and presented the world with Git?

        Can someone please make Linus go on vacation again so he can write a decent init system?

        It should only take him a few weeks... I'd rent one of those giant cement mixers (clean of course) to make dump trucks worth of popcorn to watch Linus go full rage on little bitch face beyond fucktarded Poettering.

        • (Score: 0) by Anonymous Coward on Saturday June 06 2020, @08:02PM

          by Anonymous Coward on Saturday June 06 2020, @08:02PM (#1004306)

          I mean it, I'm not even drunk.