linux-kernel - Re: [PATCH v14 08/17] mm, arm64: untag user pointers in get_vaddr

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Message-ID: <CAAeHK+wCyCa-5=bPNwfivP6sEODOXKE1bPjcjc2y_T4rN+-6gA@mail.gmail.com>
Date:   Mon, 6 May 2019 15:53:01 +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>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-rdma@...r.kernel.org, linux-media@...r.kernel.org,
        kvm@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>, Kuehling@...gle.com,
        Felix <Felix.Kuehling@....com>, Deucher@...gle.com,
        Alexander <Alexander.Deucher@....com>, Koenig@...gle.com,
        Christian <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Robin Murphy <robin.murphy@....com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>
Subject: Re: [PATCH v14 08/17] mm, arm64: untag user pointers in get_vaddr_frames

On Fri, May 3, 2019 at 6:51 PM Catalin Marinas <catalin.marinas@....com> wrote:
>
> On Tue, Apr 30, 2019 at 03:25:04PM +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.
> >
> > get_vaddr_frames uses provided user pointers for vma lookups, which can
> > only by done with untagged pointers. Instead of locating and changing
> > all callers of this function, perform untagging in it.
> >
> > Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> > ---
> >  mm/frame_vector.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> > index c64dca6e27c2..c431ca81dad5 100644
> > --- a/mm/frame_vector.c
> > +++ b/mm/frame_vector.c
> > @@ -46,6 +46,8 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> >       if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
> >               nr_frames = vec->nr_allocated;
> >
> > +     start = untagged_addr(start);
> > +
> >       down_read(&mm->mmap_sem);
> >       locked = 1;
> >       vma = find_vma_intersection(mm, start, start + 1);
>
> Is this some buffer that the user may have malloc'ed? I got lost when
> trying to track down the provenience of this buffer.

The caller that I found when I was looking at this:

drivers/gpu/drm/exynos/exynos_drm_g2d.c:482
exynos_g2d_set_cmdlist_ioctl()->g2d_map_cmdlist_gem()->g2d_userptr_get_dma_addr()->get_vaddr_frames()

>
> --
> Catalin