Requirements for retpoline in Linux 4.15 (was: Re: Linux 4.15)

[Martin Steigerwald]

Hi Linus, hi everyone,

Linus Torvalds - 28.01.18, 22:52:
> details), and perhaps equally importantly, to actually get the biggest
> fix for the indirect branch mitigations, you need not just the kernel
> updates, you need to have a compiler with support for the "retpoline"
> indirect branch model.
> 
> You can do
> 
>     cat /sys/devices/system/cpu/vulnerabilities/spectre_v2
> 
> and if you don't have a compiler that supports the retpoline
> mitigations, you'll get:
> 
>     Vulnerable: Minimal generic ASM retpoline
> 
> because only the assembly code (not the C code) will have the
> retpoline mitigation. So keep that in mind.

I have:

% cat /proc/version
Linux version 4.15.0-tp520-btrfstrim+ ([â]) (gcc version 7.3.0 (Debian 
7.3.0-1)) #38 SMP PREEMPT Mon Jan 29 09:38:44 CET 2018

% grep RETPO /boot/config-4.15.0-tp520-btrfstrim+
CONFIG_RETPOLINE=y

% gcc --version | head -1
gcc (Debian 7.3.0-1) 7.3.0

% apt changelog gcc-7
gcc-7 (7.3.0-1) unstable; urgency=medium

  * GCC 7.3.0 release.
  * Ignore bootstrap comparison failures in gcc/d on alpha. Addresses: 
#888394.

 -- Matthias Klose [â]  Thu, 25 Jan 2018 12:07:10 +0100


Yet:

% grep . /sys/devices/system/cpu/vulnerabilities/*
/sys/devices/system/cpu/vulnerabilities/meltdown:Mitigation: PTI
/sys/devices/system/cpu/vulnerabilities/spectre_v1:Vulnerable
/sys/devices/system/cpu/vulnerabilities/spectre_v2:Vulnerable: Minimal generic 
ASM retpoline


>From what I read gcc 7.3 was supposed to include back ported retpoline 
patches. What am I missing here?

Thanks,
-- 
Martin