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Date: Tue, 29 Apr 2014 15:27:49 +0200
From: Antonios Motakis <a.motakis@...tualopensystems.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: kvm-arm <kvmarm@...ts.cs.columbia.edu>,
Linux IOMMU <iommu@...ts.linux-foundation.org>,
VirtualOpenSystems Technical Team <tech@...tualopensystems.com>,
alvise rigo <a.rigo@...tualopensystems.com>,
KVM devel mailing list <kvm@...r.kernel.org>,
Christoffer Dall <christoffer.dall@...aro.org>,
Will Deacon <will.deacon@....com>,
Kim Phillips <kim.phillips@...escale.com>,
Stuart Yoder <stuart.yoder@...escale.com>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 07/11] VFIO_PLATFORM: Read and write support for
the device fd
On Mon, Apr 28, 2014 at 7:24 PM, Alex Williamson
<alex.williamson@...hat.com> 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@...tualopensystems.com>
>> ---
>> 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
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