linux-kernel - Re: [PATCH v16 05/16] arm64: untag user pointers passed to memory syscalls

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Message-ID: <CAAeHK+wkA8PskRrdfJ7MMr+je+x71WW3yDgWajxPRPwPBRNVfA@mail.gmail.com>
Date:   Wed, 12 Jun 2019 13:13:08 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
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        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
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        Robin Murphy <robin.murphy@....com>,
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        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v16 05/16] arm64: untag user pointers passed to memory syscalls

On Tue, Jun 11, 2019 at 7:45 PM Catalin Marinas <catalin.marinas@....com> wrote:
>
> On Tue, Jun 11, 2019 at 05:35:31PM +0200, Andrey Konovalov wrote:
> > On Mon, Jun 10, 2019 at 4:28 PM Catalin Marinas <catalin.marinas@....com> wrote:
> > > On Mon, Jun 03, 2019 at 06:55:07PM +0200, Andrey Konovalov wrote:
> > > > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > > > pass tagged user pointers (with the top byte set to something else other
> > > > than 0x00) as syscall arguments.
> > > >
> > > > This patch allows tagged pointers to be passed to the following memory
> > > > syscalls: get_mempolicy, madvise, mbind, mincore, mlock, mlock2, mprotect,
> > > > mremap, msync, munlock.
> > > >
> > > > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > >
> > > I would add in the commit log (and possibly in the code with a comment)
> > > that mremap() and mmap() do not currently accept tagged hint addresses.
> > > Architectures may interpret the hint tag as a background colour for the
> > > corresponding vma. With this:
> >
> > I'll change the commit log. Where do you you think I should put this
> > comment? Before mmap and mremap definitions in mm/?
>
> On arm64 we use our own sys_mmap(). I'd say just add a comment on the
> generic mremap() just before the untagged_addr() along the lines that
> new_address is not untagged for preserving similar behaviour to mmap().

Will do in v17, thanks!

>
> --
> Catalin