Next Linux Kernel Bringing "Speculative Store Bypass Safe" For ARMv8.5
Written by Michael Larabel in Security on 7 October 2018 at 06:11 AM EDT. 1 Comment
SECURITY --
Speculative Store Bypass Safe (SSBS) is a new bit added with ARMv8.5-A for SoCs moving forward like the ARM Cortex-A76 as a means for mitigation against Spectre V4.

Queued within the ARM64/AArch64 for the upcoming Linux 4.20~5.0 cycle is detection for SSBS and the ability to advertise its presence to user-space. This Speculative Store Bypass Safe functionality relies on the ARM Linux infrastructure that's already existing for Speculative Store Bypass Disable (SSBD).

This initial ARMv8.5 SSBS code is queued in ARM64 for-next/core ahead of this next kernel cycle that will be kicking off as soon as a week from today if the rest of the Linux 4.19 kernel cycle wraps up nicely.

SSBS should help with the ARM performance while fending off Spectre Variant 4, but ARM hasn't published much documentation on this ARMv8.5 addition yet nor any formal performance metrics of the impact. ARMv8.5 also brings other additions for protecting against Spectre as we've seen on the compiler front too with new speculation restriction system registers and SSBB / PSSBB speculation barriers.

ARMv8.5 though isn't just about dealing with Spectre fallout as it also has new persistent memory instructions, memory tagging, virtualization enhancements, and new random number instructions too. The first ARMv8.5 hardware should be out in 2019.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 10,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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