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

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

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@....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