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From: Andrey Konovalov <andreyknvl@google.com>
Date: Fri, 9 Mar 2018 18:58:00 +0100
Message-ID: <CAAeHK+xTEp-jcMDxNK4kCKcNtVbu4s4VXxzThsKMMFaTdBv0RQ@mail.gmail.com>
Subject: Re: [RFC PATCH 0/6] arm64: untag user pointers passed to the kernel
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To: Robin Murphy <robin.murphy@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Mark Rutland <mark.rutland@arm.com>, Al Viro <viro@zeniv.linux.org.uk>, Philippe Ombredanne <pombredanne@nexb.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Thomas Gleixner <tglx@linutronix.de>, Kate Stewart <kstewart@linuxfoundation.org>, Andrew Morton <akpm@linux-foundation.org>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Ingo Molnar <mingo@kernel.org>, "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>, Minchan Kim <minchan@kernel.org>, Michal Hocko <mhocko@suse.com>, Shaohua Li <shli@fb.com>, Andrea Arcangeli <aarcange@redhat.com>, Anshuman Khandual <khandual@linux.vnet.ibm.com>, Mike Rapoport <rppt@linux.vnet.ibm.com>, Vlastimil Babka <vbabka@suse.cz>, Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, Shakeel Butt <shakeelb@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Hugh Dickins <hughd@google.com>, Mel Gorman <mgorman@techsingularity.net>, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, Mike Kravetz <mike.kravetz@oracle.com>, Zi Yan <zi.yan@cs.rutgers.edu>, Linux ARM <linux-arm-kernel@lists.infradead.org>, LKML <linux-kernel@vger.kernel.org>, Linux Memory Management List <linux-mm@kvack.org>, Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Vineet Gupta <vgupta@synopsys.com>, Russell King <linux@armlinux.org.uk>, Mark Salter <msalter@redhat.com>, Aurelien Jacquiot <jacquiot.aurelien@gmail.com>, Mikael Starvik <starvik@axis.com>, Jesper Nilsson <jesper.nilsson@axis.com>, Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>, Geert Uytterhoeven <geert@linux-m68k.org>, James Hogan <jhogan@kernel.org>, Michal Simek <monstr@monstr.eu>, Ralf Baechle <ralf@linux-mips.org>, David Howells <dhowells@redhat.com>, Ley Foon Tan <lftan@altera.com>, Jonas Bonn <jonas@southpole.se>, Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>, Stafford Horne <shorne@gmail.com>, "James E . J . Bottomley" <jejb@parisc-linux.org>, Helge Deller <deller@gmx.de>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>, Palmer Dabbelt <palmer@sifive.com>, Albert Ou <albert@sifive.com>, Chen Liqin <liqin.linux@gmail.com>, Lennox Wu <lennox.wu@gmail.com>, Yoshinori Sato <ysato@users.sourceforge.jp>, Rich Felker <dalias@libc.org>, "David S . Miller" <davem@davemloft.net>, Ingo Molnar <mingo@redhat.com>, the arch/x86 maintainers <x86@kernel.org>, Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>, Arnd Bergmann <arnd@arndb.de>, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, adi-buildroot-devel@lists.sourceforge.net, linux-c6x-dev@linux-c6x.org, linux-cris-kernel@axis.com, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-metag@vger.kernel.org, linux-mips@linux-mips.org, linux-am33-list@redhat.com, nios2-dev@lists.rocketboards.org, openrisc@lists.librecores.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Dmitry Vyukov <dvyukov@google.com>, Kostya Serebryany <kcc@google.com>, Evgeniy Stepanov <eugenis@google.com>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>

On Fri, Mar 9, 2018 at 3:15 PM, Robin Murphy <robin.murphy@arm.com> wrote:
> Hi Andrey,
>
> On 09/03/18 14:01, Andrey Konovalov wrote:
>>
>> arm64 has a feature called Top Byte Ignore, which allows to embed pointer
>> tags into the top byte of each pointer. Userspace programs (such as
>> HWASan, a memory debugging tool [1]) might use this feature and pass
>> tagged user pointers to the kernel through syscalls or other interfaces.
>
>
> If you propose changing the ABI, then
> Documentation/arm64/tagged-pointers.txt needs to reflect the new one, since
> passing nonzero tags via syscalls is currently explicitly forbidden.
>
> Robin.

Hi Robin!

I will include changes to Documentation/arm64/tagged-pointers.txt in
the next version.

Thanks!