Re: [RFC PATCH v5 07/11] VFIO_PLATFORM: Read and write support for the device fd

[Antonios Motakis]

On Mon, Apr 28, 2014 at 7:24 PM, Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
> On Mon, 2014-04-28 at 17:52 +0200, Antonios Motakis wrote:
>> VFIO returns a file descriptor which we can use to manipulate the memory
>> regions of the device. Since some memory regions we cannot mmap due to
>> security concerns, we also allow to read and write to this file descriptor
>> directly.
>
> If there are regions we cannot mmap for security, why do we provide full
> read/write access to them?

What I refer to here is to the problem of mmaping an MMIO region that
is not page-sized. For example if it is just a small number of
registers which are not aligned on a page boundary, mmaping them would
still make the whole page accessible to the guest, with unpredictable
outcomes. But in these cases read/write is still OK.

>
>> Signed-off-by: Antonios Motakis <a.motakis@xxxxxxxxxxxxxxxxxxxxxx>
>> ---
>>  drivers/vfio/platform/vfio_platform.c | 110 +++++++++++++++++++++++++++++++++-
>>  1 file changed, 107 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vfio/platform/vfio_platform.c b/drivers/vfio/platform/vfio_platform.c
>> index 5430cbe..7c01ced 100644
>> --- a/drivers/vfio/platform/vfio_platform.c
>> +++ b/drivers/vfio/platform/vfio_platform.c
>> @@ -55,7 +55,8 @@ static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
>>
>>               region.addr = res->start;
>>               region.size = resource_size(res);
>> -             region.flags = 0;
>> +             region.flags = VFIO_REGION_INFO_FLAG_READ
>> +                             | VFIO_REGION_INFO_FLAG_WRITE;
>>
>>               vdev->region[i] = region;
>>       }
>> @@ -153,13 +154,116 @@ static long vfio_platform_ioctl(void *device_data,
>>  static ssize_t vfio_platform_read(void *device_data, char __user *buf,
>>                            size_t count, loff_t *ppos)
>>  {
>> -     return 0;
>> +     struct vfio_platform_device *vdev = device_data;
>> +     unsigned int index = VFIO_PLATFORM_OFFSET_TO_INDEX(*ppos);
>> +     loff_t off = *ppos & VFIO_PLATFORM_OFFSET_MASK;
>> +     unsigned int done = 0;
>> +     void __iomem *io;
>> +
>> +     if (index >= vdev->num_regions)
>> +             return -EINVAL;
>> +
>> +     io = ioremap_nocache(vdev->region[index].addr,
>> +                          vdev->region[index].size);
>
> I haven't looked at ioremap on arm, but if it's remotely non-trivially,
> it's probably a good idea to do this only on first access, cache it, and
> unmap it on region cleanup.  Thanks,

Ack.

>
> Alex
>
>> +
>> +     while (count) {
>> +             size_t filled;
>> +
>> +             if (count >= 4 && !(off % 4)) {
>> +                     u32 val;
>> +
>> +                     val = ioread32(io + off);
>> +                     if (copy_to_user(buf, &val, 4))
>> +                             goto err;
>> +
>> +                     filled = 4;
>> +             } else if (count >= 2 && !(off % 2)) {
>> +                     u16 val;
>> +
>> +                     val = ioread16(io + off);
>> +                     if (copy_to_user(buf, &val, 2))
>> +                             goto err;
>> +
>> +                     filled = 2;
>> +             } else {
>> +                     u8 val;
>> +
>> +                     val = ioread8(io + off);
>> +                     if (copy_to_user(buf, &val, 1))
>> +                             goto err;
>> +
>> +                     filled = 1;
>> +             }
>> +
>> +
>> +             count -= filled;
>> +             done += filled;
>> +             off += filled;
>> +             buf += filled;
>> +     }
>> +
>> +     iounmap(io);
>> +     return done;
>> +err:
>> +     iounmap(io);
>> +     return -EFAULT;
>>  }
>>
>>  static ssize_t vfio_platform_write(void *device_data, const char __user *buf,
>>                             size_t count, loff_t *ppos)
>>  {
>> -     return 0;
>> +     struct vfio_platform_device *vdev = device_data;
>> +     unsigned int index = VFIO_PLATFORM_OFFSET_TO_INDEX(*ppos);
>> +     loff_t off = *ppos & VFIO_PLATFORM_OFFSET_MASK;
>> +     unsigned int done = 0;
>> +     void __iomem *io;
>> +
>> +     if (index >= vdev->num_regions)
>> +             return -EINVAL;
>> +
>> +     io = ioremap_nocache(vdev->region[index].addr,
>> +                          vdev->region[index].size);
>> +
>> +     while (count) {
>> +             size_t filled;
>> +
>> +             if (count >= 4 && !(off % 4)) {
>> +                     u32 val;
>> +
>> +                     if (copy_from_user(&val, buf, 4))
>> +                             goto err;
>> +                     iowrite32(val, io + off);
>> +
>> +                     filled = 4;
>> +             } else if (count >= 2 && !(off % 2)) {
>> +                     u16 val;
>> +
>> +                     if (copy_from_user(&val, buf, 2))
>> +                             goto err;
>> +                     iowrite16(val, io + off);
>> +
>> +                     filled = 2;
>> +             } else {
>> +                     u8 val;
>> +
>> +                     if (copy_from_user(&val, buf, 1))
>> +                             goto err;
>> +                     iowrite8(val, io + off);
>> +
>> +                     filled = 1;
>> +             }
>> +
>> +             count -= filled;
>> +             done += filled;
>> +             off += filled;
>> +             buf += filled;
>> +     }
>> +
>> +     iounmap(io);
>> +     return done;
>> +err:
>> +     iounmap(io);
>> +     return -EFAULT;
>>  }
>>
>>  static int vfio_platform_mmap(void *device_data, struct vm_area_struct *vma)
>
>
>



-- 
Antonios Motakis
Virtual Open Systems
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/