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From: Andrey Konovalov <andreyknvl@google.com>
Date: Thu, 3 May 2018 16:09:56 +0200
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Subject: Re: [PATCH 4/6] mm, arm64: untag user addresses in mm/gup.c
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Jonathan Corbet <corbet@lwn.net>, Mark Rutland <mark.rutland@arm.com>, Robin Murphy <robin.murphy@arm.com>, Al Viro <viro@zeniv.linux.org.uk>, James Morse <james.morse@arm.com>, Kees Cook <keescook@chromium.org>, Bart Van Assche <bart.vanassche@wdc.com>, Kate Stewart <kstewart@linuxfoundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Thomas Gleixner <tglx@linutronix.de>, Philippe Ombredanne <pombredanne@nexb.com>, Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@kernel.org>, Dan Williams <dan.j.williams@intel.com>, "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>, Zi Yan <zi.yan@cs.rutgers.edu>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, Linux Memory Management List <linux-mm@kvack.org>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Lee Smith <Lee.Smith@arm.com>, Kostya Serebryany <kcc@google.com>, Dmitry Vyukov <dvyukov@google.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Evgeniy Stepanov <eugenis@google.com>

On Wed, May 2, 2018 at 7:25 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> On Wed, May 2, 2018 at 5:36 PM, Kirill A. Shutemov
> <kirill.shutemov@linux.intel.com> wrote:
>> On Wed, May 02, 2018 at 02:38:42PM +0000, Andrey Konovalov wrote:
>>> > Does having a tagged address here makes any difference? I couldn't hit a
>>> > failure with my simple tests (LD_PRELOAD a library that randomly adds
>>> > tags to pointers returned by malloc).
>>>
>>> I think you're right, follow_page_mask is only called from
>>> __get_user_pages, which already untagged the address. I'll remove
>>> untagging here.
>>
>> It also called from follow_page(). Have you covered all its callers?
>
> Oh, missed that, will take a look.

I wasn't able to find anything that calls follow_page with pointers
passed from userspace except for the memory subsystem syscalls, and we
deliberately don't add untagging in those.