linux-kernel - Re: Limits for ION Memory Allocator

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Date:   Wed, 24 Jul 2019 13:23:50 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     alex.popov@...ux.com, Sumit Semwal <sumit.semwal@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <christian@...uner.io>,
        Riley Andrews <riandrews@...roid.com>,
        driverdevel <devel@...verdev.osuosl.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Brian Starkey <brian.starkey@....com>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Mark Brown <broonie@...nel.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Linux-MM <linux-mm@...ck.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Alistair Delva <adelva@...gle.com>
Subject: Re: Limits for ION Memory Allocator

On Wed, Jul 24, 2019 at 1:18 PM John Stultz <john.stultz@...aro.org> wrote:
>
> On Wed, Jul 24, 2019 at 12:36 PM Laura Abbott <labbott@...hat.com> wrote:
> >
> > On 7/17/19 12:31 PM, Alexander Popov wrote:
> > > Hello!
> > >
> > > The syzkaller [1] has a trouble with fuzzing the Linux kernel with ION Memory
> > > Allocator.
> > >
> > > Syzkaller uses several methods [2] to limit memory consumption of the userspace
> > > processes calling the syscalls for testing the kernel:
> > >   - setrlimit(),
> > >   - cgroups,
> > >   - various sysctl.
> > > But these methods don't work for ION Memory Allocator, so any userspace process
> > > that has access to /dev/ion can bring the system to the out-of-memory state.
> > >
> > > An example of a program doing that:
> > >
> > >
> > > #include <sys/types.h>
> > > #include <sys/stat.h>
> > > #include <fcntl.h>
> > > #include <stdio.h>
> > > #include <linux/types.h>
> > > #include <sys/ioctl.h>
> > >
> > > #define ION_IOC_MAGIC         'I'
> > > #define ION_IOC_ALLOC         _IOWR(ION_IOC_MAGIC, 0, \
> > >                                     struct ion_allocation_data)
> > >
> > > struct ion_allocation_data {
> > >       __u64 len;
> > >       __u32 heap_id_mask;
> > >       __u32 flags;
> > >       __u32 fd;
> > >       __u32 unused;
> > > };
> > >
> > > int main(void)
> > > {
> > >       unsigned long i = 0;
> > >       int fd = -1;
> > >       struct ion_allocation_data data = {
> > >               .len = 0x13f65d8c,
> > >               .heap_id_mask = 1,
> > >               .flags = 0,
> > >               .fd = -1,
> > >               .unused = 0
> > >       };
> > >
> > >       fd = open("/dev/ion", 0);
> > >       if (fd == -1) {
> > >               perror("[-] open /dev/ion");
> > >               return 1;
> > >       }
> > >
> > >       while (1) {
> > >               printf("iter %lu\n", i);
> > >               ioctl(fd, ION_IOC_ALLOC, &data);
> > >               i++;
> > >       }
> > >
> > >       return 0;
> > > }
> > >
> > >
> > > I looked through the code of ion_alloc() and didn't find any limit checks.
> > > Is it currently possible to limit ION kernel allocations for some process?
> > >
> > > If not, is it a right idea to do that?
> > > Thanks!
> > >
> >
> > Yes, I do think that's the right approach. We're working on moving Ion
> > out of staging and this is something I mentioned to John Stultz. I don't
> > think we've thought too hard about how to do the actual limiting so
> > suggestions are welcome.
>
> In part the dmabuf heaps allow for separate heap devices, so we can
> have finer grained permissions to the specific heaps.  But that
> doesn't provide any controls on how much memory one process could
> allocate using the device if it has permission.
>
> I suspect the same issue is present with any of the dmabuf exporters
> (gpu/display drivers, etc), so this is less of an ION/dmabuf heap
> issue and more of a dmabuf core accounting issue.
>

Also, do unmapped memfd buffers have similar accounting issues?

thanks
-john