Re: [gentoo-user] x86.c:(.text+0xb2): undefined reference to `l1tf_vmx_mitigation' with linux kernel 4.18.1

[Alexander Kapshuk]

On Fri, Aug 17, 2018 at 8:10 AM <tuxic@××××××.de> wrote:
>
> On 08/17 02:53, Adam Carter wrote:
> > On Fri, Aug 17, 2018 at 1:15 PM, <tuxic@××××××.de> wrote:
> >
> > > Hi,
> > >
> > > CPU bugs seem to be more and more common:
> > > https://www.heise.de/security/meldung/Linux-Kernel-und-
> > > Distributionen-schuetzen-vor-Prozessorluecke-Foreshadow-L1TF-4137264.html
> > > https://www.heise.de/security/meldung/Spectre-NG-Foreshadow-
> > > gefaehrdet-Intel-Prozessoren-4137209.html
> > > (sorry, I only know of this german spoken references...)
> > >
> > > With Linux kernel 4.18.1 Linus has introduced a fix (aka workaround)
> > > of the  Foreshadow bug.
> > >
> >
> >  4.18, 4.17, 4.14, 4.9, and 4.4 have all had the fixes applied.
> >
> > >
> > > Unfortunately compiling that kernel (as downloaded from
> > > https://mirrors.edge.kernel.org/pub/linux/kernel/v4.x/ )
> > >
> > > gives me this bug:
> > >
> >
> > gentoo-sources with gcc 7.3 builds fine for me.
> >
> > Intel: grep . /sys/devices/system/cpu/vulnerabilities/*
> > /sys/devices/system/cpu/vulnerabilities/l1tf:Mitigation: PTE Inversion
> > /sys/devices/system/cpu/vulnerabilities/meltdown:Mitigation: PTI
> > /sys/devices/system/cpu/vulnerabilities/spec_store_bypass:Mitigation:
> > Speculative Store Bypass disabled via prctl and seccomp
> > /sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: __user
> > pointer sanitization
> > /sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full generic
> > retpoline, IBPB, IBRS_FW
> >
> > AMD: grep . /sys/devices/system/cpu/vulnerabilities/*
> > /sys/devices/system/cpu/vulnerabilities/l1tf:Not affected
> > /sys/devices/system/cpu/vulnerabilities/meltdown:Not affected
> > /sys/devices/system/cpu/vulnerabilities/spec_store_bypass:Mitigation:
> > Speculative Store Bypass disabled via prctl and seccomp
> > /sys/devices/system/cpu/vulnerabilities/spectre_v1:Mitigation: __user
> > pointer sanitization
> > /sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full AMD
> > retpoline, IBPB
>
> Hi,
>
> I am happy, that other sources do work for you Adam.
>
> Interesting would be, why the original sources does not compile for
> me.
> Any idea?
>
>
>

This problem has been reported upstream. See below.
https://lkml.org/lkml/2018/8/15/118

In particular:

Build is successful with
CONFIG_KVM=y
CONFIG_KVM_INTEL=y
CONFIG_KVM_AMD=y
but fails if only
CONFIG_KVM=y
CONFIG_KVM_AMD=y
are selected.