linux-kernel - Re: [RESEND RFC PATCH] x86/bugs: Add "unknown" reporting for MMIO Stale Data

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Message-ID: <20220729174521.kvbudqlpsoyvxzrv@desk>
Date:   Fri, 29 Jul 2022 10:45:21 -0700
From:   'Pawan Gupta' <pawan.kumar.gupta@...ux.intel.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Borislav Petkov <bp@...en8.de>, Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "antonio.gomez.iglesias@...ux.intel.com" 
        <antonio.gomez.iglesias@...ux.intel.com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [RESEND RFC PATCH] x86/bugs: Add "unknown" reporting for MMIO
 Stale Data

On Fri, Jul 29, 2022 at 10:40:20AM +0000, David Laight wrote:
> From: Pawan Gupta
> > Sent: 29 July 2022 03:29
> > 
> > On Thu, Jul 28, 2022 at 02:00:13PM +0200, Borislav Petkov wrote:
> > > On Thu, Jul 14, 2022 at 06:30:18PM -0700, Pawan Gupta wrote:
> > > > Older CPUs beyond its Servicing period are not listed in the affected
> > > > processor list for MMIO Stale Data vulnerabilities. These CPUs currently
> > > > report "Not affected" in sysfs, which may not be correct.
> 
> I looked this up....
> 
> The mitigations seem to rely on unprivileged code not being able
> to do MMIO accesses.
> That isn't true, device drivers can mmap PCIe addresses directly
> into user program address space.
> While unlikely, there is no reason this can't be supported for
> non-root processes.

Agree. Would it be fair to assume that processes that get direct
hardware access are trusted?