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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: 2) by maxwell demon on Friday June 05 2020, @05:10PM (2 children)

    by maxwell demon (1608) on Friday June 05 2020, @05:10PM (#1003837) Journal

    I remember a time once, in a different millennium, when there was an effort to have a reduced simpler set of machine instructions, and do optimizations in compilers?

    Wasn't Intel's Itanium meant to be exactly this?

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  • (Score: 0) by Anonymous Coward on Friday June 05 2020, @05:17PM

    by Anonymous Coward on Friday June 05 2020, @05:17PM (#1003844)

    So fitting was nickname that to this day I read the actual name as a reference to the Titanic.

  • (Score: 5, Interesting) by TheReaperD on Friday June 05 2020, @05:23PM

    by TheReaperD (5556) on Friday June 05 2020, @05:23PM (#1003849)

    No, Itanium was an IP power grab on Intel's part. The licencing was such that Intel would own the IP of all compilers and their code for Itanium systems. Jumping architectures was a roadblock, but it was really the IP issues that spelled Itanium's doom when AMD offered an alternative with the x86-AMD64 instruction set. (And yes, that is the 64-bit x86 instruction set's name despite Intel's attempt to rename it.)

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