linux-kernel - Re: [PATCH] Ability to read the MKTME status from userspace

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Message-ID: <20200619134432.GE32683@zn.tnic>
Date:   Fri, 19 Jun 2020 15:44:32 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Richard Hughes <hughsient@...il.com>
Cc:     Daniel Gutson <daniel@...ypsium.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>, Tony Luck <tony.luck@...el.com>,
        Rahul Tanwar <rahul.tanwar@...ux.intel.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Ability to read the MKTME status from userspace

On Fri, Jun 19, 2020 at 02:31:11PM +0100, Richard Hughes wrote:
> 1. that the CPU supports TME (->cpuid, already done)
> 2. that the platform has not disabled TME in some way

Yes, this is what I'm proposing with clearing the flag in /proc/cpuinfo.
The needed information is there:

1. TME in CPUID
2. TME *not* in /proc/cpuinfo

which means the platform doesn't support it.

If we are going to export a list of features which the OS
kernel/platform has enabled - and this means a contract between kernel
and userspace - then this should not be a misc driver which gets loaded
as a module but builtin, maybe a proper sysfs layout similar to

/sys/devices/system/cpu/vulnerabilities

which userspace can use. Along with proper ABI definition, design,
documentation and all that belongs to a proper interface with userspace.
Because once userspace uses it, it is practically cast in stone.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette