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Date:   Fri, 31 May 2019 17:46:05 +0100
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     Andrey Konovalov <andreyknvl@google.com>
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Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel
Message-ID: <20190531164605.GC3568@arrakis.emea.arm.com>
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On Fri, May 31, 2019 at 06:24:06PM +0200, Andrey Konovalov wrote:
> On Fri, May 31, 2019 at 6:20 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > On Fri, May 31, 2019 at 04:29:10PM +0200, Andrey Konovalov wrote:
> > > On Thu, May 30, 2019 at 7:15 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > > On Tue, May 28, 2019 at 04:14:45PM +0200, Andrey Konovalov wrote:
> > > > > Thanks for a lot of valuable input! I've read through all the replies
> > > > > and got somewhat lost. What are the changes I need to do to this
> > > > > series?
> > > > >
> > > > > 1. Should I move untagging for memory syscalls back to the generic
> > > > > code so other arches would make use of it as well, or should I keep
> > > > > the arm64 specific memory syscalls wrappers and address the comments
> > > > > on that patch?
> > > >
> > > > Keep them generic again but make sure we get agreement with Khalid on
> > > > the actual ABI implications for sparc.
> > >
> > > OK, will do. I find it hard to understand what the ABI implications
> > > are. I'll post the next version without untagging in brk, mmap,
> > > munmap, mremap (for new_address), mmap_pgoff, remap_file_pages, shmat
> > > and shmdt.
> >
> > It's more about not relaxing the ABI to accept non-zero top-byte unless
> > we have a use-case for it. For mmap() etc., I don't think that's needed
> > but if you think otherwise, please raise it.
> >
> > > > > 2. Should I make untagging opt-in and controlled by a command line argument?
> > > >
> > > > Opt-in, yes, but per task rather than kernel command line option.
> > > > prctl() is a possibility of opting in.
> > >
> > > OK. Should I store a flag somewhere in task_struct? Should it be
> > > inheritable on clone?
> >
> > A TIF flag would do but I'd say leave it out for now (default opted in)
> > until we figure out the best way to do this (can be a patch on top of
> > this series).
> 
> You mean leave the whole opt-in/prctl part out? So the only change
> would be to move untagging for memory syscalls into generic code?

Yes (or just wait until next week to see if the discussion settles
down).

-- 
Catalin