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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Fri, 31 May 2019 18:24:06 +0200
Message-ID: <CAAeHK+zRDD7ZPPUA9cpwHOdgTRrJLWAby8Wg9oPgmhqMpHwvFw@mail.gmail.com>
Subject: Re: [PATCH v15 00/17] arm64: untag user pointers passed to the kernel
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Evgenii Stepanov <eugenis@google.com>,
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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?

>
> Thanks.
>
> --
> Catalin