Linux Readying Spectre V2 Userspace-Userspace Protection

[phoronix]

Phoronix: Linux Readying Spectre V2 Userspace-Userspace Protection

While the Linux kernel has been patched for months (and updated CPU microcode available) to mitigate Spectre Variant Two "Branch Target Injection" this has been focused on kernel-space protection while patches are pending now for userspace-userspace protection...

http://www.phoronix.com/scan.php?page=news_item&px=Linux-Spectre-V2-Userspace

[ms178]

I hope the hardware fixes will be available in the not too distant future to make all of this performance reducing work obsolete. Considering all of the time and effort (costs) going into these mitigations which could have been spend on performance improvements instead makes me a little sad.

[dsmithhfx]

What a mess.

[Illasera]

Can we opt-out of the whole spectre/meltdown fixes when we update the kernel?

they don't help and only slow things down, this is based on experimentation i made with spectre in previous versions...

It is useless to fight back, Only new architecture will help.

[Tomin]

Can we opt-out of the whole spectre/meltdown fixes when we update the kernel?

You can always tell your kernel to not to use these fixes with boot parameters. You can find it easily by searching internet but for your convenience, here is what Michael wrote about it a short while ago:

https://www.phoronix.com/scan.php?page=news_item&px=Global-Switch-Skip-Spectre-Melt

I don't know if there is config option for disabling these in case you are compiling your own kernels. I imagined that you use some prepackaged kernel of distribution of your choice since you had to ask here.

[DrYak]

Note that, as of today, Intel are the only CPUs where the spectre-v2 address table poisoning has been demonstrated successfully.

There are a few AMD the could in theory be affected (they to indirect branch prediction speculation) but it apparently it's much more complicated to actually pull an exploit.