linux-kernel - Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel

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Message-ID: <20190523201105.oifkksus4rzcwqt4@mbp>
Date:   Thu, 23 May 2019 21:11:05 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Khalid Aziz <khalid.aziz@...cle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-rdma@...r.kernel.org, linux-media@...r.kernel.org,
        kvm@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
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        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Elliott Hughes <enh@...gle.com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel

Hi Khalid,

On Thu, May 23, 2019 at 11:51:40AM -0600, Khalid Aziz wrote:
> On 5/21/19 6:04 PM, Kees Cook wrote:
> > As an aside: I think Sparc ADI support in Linux actually side-stepped
> > this[1] (i.e. chose "solution 1"): "All addresses passed to kernel must
> > be non-ADI tagged addresses." (And sadly, "Kernel does not enable ADI
> > for kernel code.") I think this was a mistake we should not repeat for
> > arm64 (we do seem to be at least in agreement about this, I think).
> > 
> > [1] https://lore.kernel.org/patchwork/patch/654481/
> 
> That is a very early version of the sparc ADI patch. Support for tagged
> addresses in syscalls was added in later versions and is in the patch
> that is in the kernel.

I tried to figure out but I'm not familiar with the sparc port. How did
you solve the tagged address going into various syscall implementations
in the kernel (e.g. sys_write)? Is the tag removed on kernel entry or it
ends up deeper in the core code?

Thanks.

-- 
Catalin