Re: [RFC][PATCH 0/3] arm64 relaxed ABI

From: Catalin Marinas <catalin.marinas@arm.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Will Deacon <will.deacon@arm.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>,
	Chintan Pandya <cpandya@codeaurora.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Jacob Bramley <Jacob.Bramley@arm.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Kees Cook <keescook@chromium.org>,
	Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
	Lee Smith <Lee.Smith@arm.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Kostya Serebryany <kcc@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Robin Murphy <robin.murphy@arm.com>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: Re: [RFC][PATCH 0/3] arm64 relaxed ABI
Date: Tue, 18 Dec 2018 17:59:38 +0000	[thread overview]
Message-ID: <20181218175938.GD20197@arrakis.emea.arm.com> (raw)
In-Reply-To: <CAAeHK+zxYJDJ7DJuDAOuOMgGvckFwMAoVUTDJzb6MX3WsXhRTQ@mail.gmail.com>

On Tue, Dec 18, 2018 at 04:03:38PM +0100, Andrey Konovalov wrote:
> On Wed, Dec 12, 2018 at 4:02 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > The summary of our internal discussions (mostly between kernel
> > developers) is that we can't properly describe a user ABI that covers
> > future syscalls or syscall extensions while not all syscalls accept
> > tagged pointers. So we tweaked the requirements slightly to only allow
> > tagged pointers back into the kernel *if* the originating address is
> > from an anonymous mmap() or below sbrk(0). This should cover some of the
> > ioctls or getsockopt(TCP_ZEROCOPY_RECEIVE) where the user passes a
> > pointer to a buffer obtained via mmap() on the device operations.
> >
> > (sorry for not being clear on what Vincenzo's proposal implies)
> 
> OK, I see. So I need to make the following changes to my patchset AFAIU.
> 
> 1. Make sure that we only allow tagged user addresses that originate
> from an anonymous mmap() or below sbrk(0). How exactly should this
> check be performed?

I don't think we should perform such checks. That's rather stating that
the kernel only guarantees that the tagged pointers work if they
originated from these memory ranges.

> 2. Allow tagged addressed passed to memory syscalls (as long as (1) is
> satisfied). Do I understand correctly that this means that I need to
> locate all find_vma() callers outside of mm/ and fix them up as well?

Yes (unless anyone as a better idea or objections to this approach).

BTW, I'll be off until the new year, so won't be able to follow up.

-- 
Catalin