linux-kernel - Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

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Date:   Mon, 8 Jan 2018 08:33:43 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dominik Brodowski <linux@...inikbrodowski.net>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Dave Hansen <dave.hansen@...el.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [patch V2 1/2] sysfs/cpu: Add vulnerability folder

On Mon, 8 Jan 2018, Dominik Brodowski wrote:
> On Sun, Jan 07, 2018 at 10:48:00PM +0100, Thomas Gleixner wrote:
> > As the meltdown/spectre problem affects several CPU architectures, it makes
> > sense to have common way to express whether a system is affected by a
> > particular vulnerability or not. If affected the way to express the
> > mitigation should be common as well.
> > 
> > Create /sys/devices/system/cpu/vulnerabilities folder and files for
> > meltdown, spectre_v1 and spectre_v2.
> > 
> > Allow architectures to override the show function.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  Documentation/ABI/testing/sysfs-devices-system-cpu |   16 +++++++
> >  drivers/base/Kconfig                               |    3 +
> >  drivers/base/cpu.c                                 |   48 +++++++++++++++++++++
> >  include/linux/cpu.h                                |    7 +++
> >  4 files changed, 74 insertions(+)
> > 
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -373,3 +373,19 @@ Contact:	Linux kernel mailing list <linu
> >  Description:	information about CPUs heterogeneity.
> >  
> >  		cpu_capacity: capacity of cpu#.
> > +
> > +What:		/sys/devices/system/cpu/vulnerabilities
> > +		/sys/devices/system/cpu/vulnerabilities/meltdown
> > +		/sys/devices/system/cpu/vulnerabilities/spectre_v1
> > +		/sys/devices/system/cpu/vulnerabilities/spectre_v2
> > +Date:		Januar 2018
> > +Contact:	Linux kernel mailing list <linux-kernel@...r.kernel.org>
> > +Description:	Information about CPU vulnerabilities
> > +
> > +		The files are named after the code names of CPU
> > +		vulnerabilities. The output of those files reflects the
> > +		state of the CPUs in the system.
> 
> Currently, your code sets X86_BUG_SPECTRE_V[12] unconditionally on x86
> CPUs. However, to my understanding some CPUs which do not execute code
> out-of-order aren't affected. As it is better to err on the safe side for
> now, what about adding a disclaimer at the end of this sentence, such as:
> 
> 	", but may contain false positives"

We do that in the same way as we did with BUG_INSECURE (now MELTDOWN). Err
out on the safe side and get the exceptions in place when people are
confident about them. It's not going to take long I assume.

Thanks,

	tglx