linux-kernel - Re: [RFC PATCH v3] sparc64: Add support for Application Data Integrity (ADI)

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Message-ID: <6fcaab9f-40fb-fdfb-2c7e-bf21a862ab7c@linux.intel.com>
Date:   Wed, 4 Jan 2017 15:27:35 -0800
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Khalid Aziz <khalid.aziz@...cle.com>, davem@...emloft.net,
        corbet@....net, arnd@...db.de, akpm@...ux-foundation.org
Cc:     hpa@...or.com, viro@...iv.linux.org.uk, nitin.m.gupta@...cle.com,
        chris.hyser@...cle.com, tushar.n.dave@...cle.com,
        sowmini.varadhan@...cle.com, mike.kravetz@...cle.com,
        adam.buchbinder@...il.com, minchan@...nel.org, hughd@...gle.com,
        kirill.shutemov@...ux.intel.com, keescook@...omium.org,
        allen.pais@...cle.com, aryabinin@...tuozzo.com,
        atish.patra@...cle.com, joe@...ches.com, pmladek@...e.com,
        jslaby@...e.cz, cmetcalf@...lanox.com,
        paul.gortmaker@...driver.com, mhocko@...e.com, jmarchan@...hat.com,
        lstoakes@...il.com, 0x7f454c46@...il.com, vbabka@...e.cz,
        tglx@...utronix.de, mingo@...hat.com, dan.j.williams@...el.com,
        iamjoonsoo.kim@....com, mgorman@...hsingularity.net,
        vdavydov.dev@...il.com, hannes@...xchg.org, namit@...are.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
        x86@...nel.org, linux-mm@...ck.org,
        Khalid Aziz <khalid@...ehiking.org>
Subject: Re: [RFC PATCH v3] sparc64: Add support for Application Data
 Integrity (ADI)

On 01/04/2017 02:46 PM, Khalid Aziz wrote:
> This patch extends mprotect to enable ADI (TSTATE.mcde), enable/disable
> MCD (Memory Corruption Detection) on selected memory ranges, enable
> TTE.mcd in PTEs, return ADI parameters to userspace and save/restore ADI
> version tags on page swap out/in. 

I'm a bit confused why we need all the mechanics with set_swp_pte_at().
For pkeys, for instance, all of the PTEs under a given VMA share a pkey.
 When swapping something in, we just get the pkey out of the VMA and
populate the PTE.

ADI doesn't seem to have a similar restriction.  The feature is turned
on or off at a VMA granularity, but we do not (or can enforce that all
pages under a given VMA must share a tag.

But this leads to an interesting question: is the tag associated with
the (populated?) pte, or the virtual address?  Can you have tags
associated with non-present addresses?  What's the mechanism that clears
the tags at munmap() or MADV_FREE time?

Is the tag storage a precious resource?  Can it be exhausted?