[PATCH 2/5] vfio: introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag

[PATCH 2/5] vfio: introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Antonios Motakis]

We introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag to the VFIO dma map call,
and expose its availability via the capability VFIO_DMA_NOEXEC_IOMMU.
This way the user can control whether the XN flag will be set on the
requested mappings. The IOMMU_NOEXEC flag needs to be available for all
the IOMMUs of the container used.

Signed-off-by: Antonios Motakis <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>
---
 include/uapi/linux/vfio.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 6612974..111b5e8 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -29,6 +29,7 @@
  * capability is subject to change as groups are added or removed.
  */
 #define VFIO_DMA_CC_IOMMU		4
+#define VFIO_DMA_NOEXEC_IOMMU		5
 
 /* Check if EEH is supported */
 #define VFIO_EEH			5
@@ -401,6 +402,7 @@ struct vfio_iommu_type1_dma_map {
 	__u32	flags;
 #define VFIO_DMA_MAP_FLAG_READ (1 << 0)		/* readable from device */
 #define VFIO_DMA_MAP_FLAG_WRITE (1 << 1)	/* writable from device */
+#define VFIO_DMA_MAP_FLAG_NOEXEC (1 << 2)	/* not executable from device */
 	__u64	vaddr;				/* Process virtual address */
 	__u64	iova;				/* IO virtual address */
 	__u64	size;				/* Size of mapping (bytes) */
-- 
2.1.1

Re: [PATCH 2/5] vfio: introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Alex Williamson]

On Mon, 2014-10-13 at 15:09 +0200, Antonios Motakis wrote:
> We introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag to the VFIO dma map call,
> and expose its availability via the capability VFIO_DMA_NOEXEC_IOMMU.
> This way the user can control whether the XN flag will be set on the
> requested mappings. The IOMMU_NOEXEC flag needs to be available for all
> the IOMMUs of the container used.
> 
> Signed-off-by: Antonios Motakis <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>
> ---
>  include/uapi/linux/vfio.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 6612974..111b5e8 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -29,6 +29,7 @@
>   * capability is subject to change as groups are added or removed.
>   */
>  #define VFIO_DMA_CC_IOMMU		4
> +#define VFIO_DMA_NOEXEC_IOMMU		5
>  
>  /* Check if EEH is supported */
>  #define VFIO_EEH			5
                                    ^^
5 is still already used.  Feel free to convert to enum so we stop making
this mistake.

> @@ -401,6 +402,7 @@ struct vfio_iommu_type1_dma_map {
>  	__u32	flags;
>  #define VFIO_DMA_MAP_FLAG_READ (1 << 0)		/* readable from device */
>  #define VFIO_DMA_MAP_FLAG_WRITE (1 << 1)	/* writable from device */
> +#define VFIO_DMA_MAP_FLAG_NOEXEC (1 << 2)	/* not executable from device */
>  	__u64	vaddr;				/* Process virtual address */
>  	__u64	iova;				/* IO virtual address */
>  	__u64	size;				/* Size of mapping (bytes) */

Re: [PATCH 2/5] vfio: introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Andy Lutomirski]

On Mon, Oct 13, 2014 at 6:09 AM, Antonios Motakis
<a.motakis@virtualopensystems.com> wrote:
> We introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag to the VFIO dma map call,
> and expose its availability via the capability VFIO_DMA_NOEXEC_IOMMU.
> This way the user can control whether the XN flag will be set on the
> requested mappings. The IOMMU_NOEXEC flag needs to be available for all
> the IOMMUs of the container used.

Since you sent this to the linux-api list, I'll bite: what's the XN
flag?  I know what PROT_EXEC does when you mmap something, and I
presume that vfio is mmappable, but I don't actually have any clue
what this patch does.

I assume that this does not have anything to do with a non-CPU DMA
master executing code in main memory, because that makes rather little
sense.  (Or maybe it really does, in which case: weird.)

--Andy

Re: [PATCH 2/5] vfio: introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Antonios Motakis]

On Mon, Oct 20, 2014 at 11:29 PM, Alex Williamson
<alex.williamson@redhat.com> wrote:
> On Mon, 2014-10-13 at 15:09 +0200, Antonios Motakis wrote:
>> We introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag to the VFIO dma map call,
>> and expose its availability via the capability VFIO_DMA_NOEXEC_IOMMU.
>> This way the user can control whether the XN flag will be set on the
>> requested mappings. The IOMMU_NOEXEC flag needs to be available for all
>> the IOMMUs of the container used.
>>
>> Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
>> ---
>>  include/uapi/linux/vfio.h | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
>> index 6612974..111b5e8 100644
>> --- a/include/uapi/linux/vfio.h
>> +++ b/include/uapi/linux/vfio.h
>> @@ -29,6 +29,7 @@
>>   * capability is subject to change as groups are added or removed.
>>   */
>>  #define VFIO_DMA_CC_IOMMU            4
>> +#define VFIO_DMA_NOEXEC_IOMMU                5
>>
>>  /* Check if EEH is supported */
>>  #define VFIO_EEH                     5
>                                     ^^
> 5 is still already used.  Feel free to convert to enum so we stop making
> this mistake.

Oops :) will do.

>
>> @@ -401,6 +402,7 @@ struct vfio_iommu_type1_dma_map {
>>       __u32   flags;
>>  #define VFIO_DMA_MAP_FLAG_READ (1 << 0)              /* readable from device */
>>  #define VFIO_DMA_MAP_FLAG_WRITE (1 << 1)     /* writable from device */
>> +#define VFIO_DMA_MAP_FLAG_NOEXEC (1 << 2)    /* not executable from device */
>>       __u64   vaddr;                          /* Process virtual address */
>>       __u64   iova;                           /* IO virtual address */
>>       __u64   size;                           /* Size of mapping (bytes) */
>
>
>



-- 
Antonios Motakis
Virtual Open Systems

Re: [PATCH 2/5] vfio: introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag

[Antonios Motakis]

On Mon, Oct 20, 2014 at 11:37 PM, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org> wrote:
> On Mon, Oct 13, 2014 at 6:09 AM, Antonios Motakis
> <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org> wrote:
>> We introduce the VFIO_DMA_MAP_FLAG_NOEXEC flag to the VFIO dma map call,
>> and expose its availability via the capability VFIO_DMA_NOEXEC_IOMMU.
>> This way the user can control whether the XN flag will be set on the
>> requested mappings. The IOMMU_NOEXEC flag needs to be available for all
>> the IOMMUs of the container used.
>
> Since you sent this to the linux-api list, I'll bite: what's the XN
> flag?  I know what PROT_EXEC does when you mmap something, and I
> presume that vfio is mmappable, but I don't actually have any clue
> what this patch does.
>
> I assume that this does not have anything to do with a non-CPU DMA
> master executing code in main memory, because that makes rather little
> sense.  (Or maybe it really does, in which case: weird.)

It does actually. For example, the ARM PL330 DMA controller will fetch
from memory code with DMA instructions, and it will respect this flag.
It is not code that can be executed on the CPU of course, but it is
executable on the DMAC.


>
> --Andy



-- 
Antonios Motakis
Virtual Open Systems