linux-kernel - Re: [PATCH v7 0/5] Add Intel IOMMU debugfs support

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Message-ID: <20180329084824.fvy7cg2wban4by4n@8bytes.org>
Date:   Thu, 29 Mar 2018 10:48:24 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     Gary R Hook <gary.hook@....com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Sohil Mehta <sohil.mehta@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Gayatri Kammela <gayatri.kammela@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v7 0/5] Add Intel IOMMU debugfs support

[ Adding Gary from AMD to Cc ]

On Mon, Mar 19, 2018 at 09:37:14AM -0700, Jacob Pan wrote:
> On Thu, 15 Mar 2018 14:18:54 +0100
> Joerg Roedel <joro@...tes.org> wrote:
> 
> > On Thu, Feb 15, 2018 at 08:38:11AM -0800, Jacob Pan wrote:
> > > Just wondering if your concern is on the implementation or the
> > > debugfs idea in general. Perhaps have some common IOMMU debugfs?  
> > 
> > My concern mainly is that we add interfaces which reveal
> > potentially security relevant information
> I don;t think security is any worse than existing kernel page table in
> debugfs. i.e. /sys/kernel/debug/page_tables
> This is a debug feature.

Okay, so here is the way to go: Please introduce a basic debugfs
facility to the core iommu code. It should basically only create a
'iommu/' directory in debugfs where drivers can create their own
sub-directories. This must be enabled by a new kconfig option
(CONFIG_IOMMU_DEBUGFS) and the kernel should print a big fat warning at
boot when it is enabled. This hopefully prevents anyone from enabling it
for production kernels.

Then in the next cycle I will review again more closely what information
about VT-d and AMD-Vi is revealed there and will probably apply what I
can live with.

Thanks,

	Joerg