[v6,02/22] drm/gem: Move mapping of imported dma-bufs to drm_gem_mmap_obj()

  Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
handle imported dma-bufs properly, which results in mapping of something
else than the imported dma-buf. For example, on NVIDIA Tegra we get a hard
lockup when userspace writes to the memory mapping of a dma-buf that was
imported into Tegra's DRM GEM.

To fix this bug, move mapping of imported dma-bufs to drm_gem_mmap_obj().
Now mmaping of imported dma-bufs works properly for all DRM drivers.

Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_gem.c              | 3 +++
 drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
 drivers/gpu/drm/tegra/gem.c            | 4 ++++
 3 files changed, 7 insertions(+), 9 deletions(-)
  

On 5/27/22 01:50, Dmitry Osipenko wrote:
> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
> handle imported dma-bufs properly, which results in mapping of something
> else than the imported dma-buf. For example, on NVIDIA Tegra we get a hard
> lockup when userspace writes to the memory mapping of a dma-buf that was
> imported into Tegra's DRM GEM.
>
> To fix this bug, move mapping of imported dma-bufs to drm_gem_mmap_obj().
> Now mmaping of imported dma-bufs works properly for all DRM drivers.
Same comment about Fixes: as in patch 1,
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
> ---
>   drivers/gpu/drm/drm_gem.c              | 3 +++
>   drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
>   drivers/gpu/drm/tegra/gem.c            | 4 ++++
>   3 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 86d670c71286..7c0b025508e4 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
>   	if (obj_size < vma->vm_end - vma->vm_start)
>   		return -EINVAL;
>   
> +	if (obj->import_attach)
> +		return dma_buf_mmap(obj->dma_buf, vma, 0);

If we start enabling mmaping of imported dma-bufs on a majority of 
drivers in this way, how do we ensure that user-space is not blindly 
using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC 
which is needed before and after cpu access of mmap'ed dma-bufs?

I was under the impression (admittedly without looking) that the few 
drivers that actually called into dma_buf_mmap() had some private 
user-mode driver code in place that ensured this happened.

/Thomas


> +
>   	/* Take a ref for this mapping of the object, so that the fault
>   	 * handler can dereference the mmap offset's pointer to the object.
>   	 * This reference is cleaned up by the corresponding vm_close
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 8ad0e02991ca..6190f5018986 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -609,17 +609,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops);
>    */
>   int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma)
>   {
> -	struct drm_gem_object *obj = &shmem->base;
>   	int ret;
>   
> -	if (obj->import_attach) {
> -		/* Drop the reference drm_gem_mmap_obj() acquired.*/
> -		drm_gem_object_put(obj);
> -		vma->vm_private_data = NULL;
> -
> -		return dma_buf_mmap(obj->dma_buf, vma, 0);
> -	}
> -
>   	ret = drm_gem_shmem_get_pages(shmem);
>   	if (ret) {
>   		drm_gem_vm_close(vma);
> diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c
> index 7c7dd84e6db8..f92aa20d63bb 100644
> --- a/drivers/gpu/drm/tegra/gem.c
> +++ b/drivers/gpu/drm/tegra/gem.c
> @@ -564,6 +564,10 @@ int __tegra_gem_mmap(struct drm_gem_object *gem, struct vm_area_struct *vma)
>   {
>   	struct tegra_bo *bo = to_tegra_bo(gem);
>   
> +	/* imported dmu-buf is mapped by drm_gem_mmap_obj()  */
> +	if (gem->import_attach)
> +		return 0;
> +
>   	if (!bo->pages) {
>   		unsigned long vm_pgoff = vma->vm_pgoff;
>   		int err;
  

On 6/29/22 09:40, Thomas Hellström (Intel) wrote:
> 
> On 5/27/22 01:50, Dmitry Osipenko wrote:
>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
>> handle imported dma-bufs properly, which results in mapping of something
>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a
>> hard
>> lockup when userspace writes to the memory mapping of a dma-buf that was
>> imported into Tegra's DRM GEM.
>>
>> To fix this bug, move mapping of imported dma-bufs to drm_gem_mmap_obj().
>> Now mmaping of imported dma-bufs works properly for all DRM drivers.
> Same comment about Fixes: as in patch 1,
>>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>> ---
>>   drivers/gpu/drm/drm_gem.c              | 3 +++
>>   drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
>>   drivers/gpu/drm/tegra/gem.c            | 4 ++++
>>   3 files changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> index 86d670c71286..7c0b025508e4 100644
>> --- a/drivers/gpu/drm/drm_gem.c
>> +++ b/drivers/gpu/drm/drm_gem.c
>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj,
>> unsigned long obj_size,
>>       if (obj_size < vma->vm_end - vma->vm_start)
>>           return -EINVAL;
>>   +    if (obj->import_attach)
>> +        return dma_buf_mmap(obj->dma_buf, vma, 0);
> 
> If we start enabling mmaping of imported dma-bufs on a majority of
> drivers in this way, how do we ensure that user-space is not blindly
> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC
> which is needed before and after cpu access of mmap'ed dma-bufs?
> 
> I was under the impression (admittedly without looking) that the few
> drivers that actually called into dma_buf_mmap() had some private
> user-mode driver code in place that ensured this happened.

Since it's a userspace who does the mapping, then it should be a
responsibility of userspace to do all the necessary syncing. I'm not
sure whether anyone in userspace really needs to map imported dma-bufs
in practice. Nevertheless, this use-case is broken and should be fixed
by either allowing to do the mapping or prohibiting it.
  

On 6/29/22 10:22, Dmitry Osipenko wrote:
> On 6/29/22 09:40, Thomas Hellström (Intel) wrote:
>> On 5/27/22 01:50, Dmitry Osipenko wrote:
>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
>>> handle imported dma-bufs properly, which results in mapping of something
>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a
>>> hard
>>> lockup when userspace writes to the memory mapping of a dma-buf that was
>>> imported into Tegra's DRM GEM.
>>>
>>> To fix this bug, move mapping of imported dma-bufs to drm_gem_mmap_obj().
>>> Now mmaping of imported dma-bufs works properly for all DRM drivers.
>> Same comment about Fixes: as in patch 1,
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>> ---
>>>    drivers/gpu/drm/drm_gem.c              | 3 +++
>>>    drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
>>>    drivers/gpu/drm/tegra/gem.c            | 4 ++++
>>>    3 files changed, 7 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>> index 86d670c71286..7c0b025508e4 100644
>>> --- a/drivers/gpu/drm/drm_gem.c
>>> +++ b/drivers/gpu/drm/drm_gem.c
>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj,
>>> unsigned long obj_size,
>>>        if (obj_size < vma->vm_end - vma->vm_start)
>>>            return -EINVAL;
>>>    +    if (obj->import_attach)
>>> +        return dma_buf_mmap(obj->dma_buf, vma, 0);
>> If we start enabling mmaping of imported dma-bufs on a majority of
>> drivers in this way, how do we ensure that user-space is not blindly
>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC
>> which is needed before and after cpu access of mmap'ed dma-bufs?
>>
>> I was under the impression (admittedly without looking) that the few
>> drivers that actually called into dma_buf_mmap() had some private
>> user-mode driver code in place that ensured this happened.
> Since it's a userspace who does the mapping, then it should be a
> responsibility of userspace to do all the necessary syncing.

Sure, but nothing prohibits user-space to ignore the syncing thinking 
"It works anyway", testing those drivers where the syncing is a NOP. And 
when a driver that finally needs syncing is tested it's too late to fix 
all broken user-space.

>   I'm not
> sure whether anyone in userspace really needs to map imported dma-bufs
> in practice. Nevertheless, this use-case is broken and should be fixed
> by either allowing to do the mapping or prohibiting it.
>
Then I'd vote for prohibiting it, at least for now. And for the future 
moving forward we could perhaps revisit the dma-buf need for syncing, 
requiring those drivers that actually need it to implement emulated 
coherent memory which can be done not too inefficiently (vmwgfx being 
one example).

/Thomas
  

On 6/29/22 11:43, Thomas Hellström (Intel) wrote:
> 
> On 6/29/22 10:22, Dmitry Osipenko wrote:
>> On 6/29/22 09:40, Thomas Hellström (Intel) wrote:
>>> On 5/27/22 01:50, Dmitry Osipenko wrote:
>>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
>>>> handle imported dma-bufs properly, which results in mapping of
>>>> something
>>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a
>>>> hard
>>>> lockup when userspace writes to the memory mapping of a dma-buf that
>>>> was
>>>> imported into Tegra's DRM GEM.
>>>>
>>>> To fix this bug, move mapping of imported dma-bufs to
>>>> drm_gem_mmap_obj().
>>>> Now mmaping of imported dma-bufs works properly for all DRM drivers.
>>> Same comment about Fixes: as in patch 1,
>>>> Cc: stable@vger.kernel.org
>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>>> ---
>>>>    drivers/gpu/drm/drm_gem.c              | 3 +++
>>>>    drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
>>>>    drivers/gpu/drm/tegra/gem.c            | 4 ++++
>>>>    3 files changed, 7 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>>> index 86d670c71286..7c0b025508e4 100644
>>>> --- a/drivers/gpu/drm/drm_gem.c
>>>> +++ b/drivers/gpu/drm/drm_gem.c
>>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj,
>>>> unsigned long obj_size,
>>>>        if (obj_size < vma->vm_end - vma->vm_start)
>>>>            return -EINVAL;
>>>>    +    if (obj->import_attach)
>>>> +        return dma_buf_mmap(obj->dma_buf, vma, 0);
>>> If we start enabling mmaping of imported dma-bufs on a majority of
>>> drivers in this way, how do we ensure that user-space is not blindly
>>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC
>>> which is needed before and after cpu access of mmap'ed dma-bufs?
>>>
>>> I was under the impression (admittedly without looking) that the few
>>> drivers that actually called into dma_buf_mmap() had some private
>>> user-mode driver code in place that ensured this happened.
>> Since it's a userspace who does the mapping, then it should be a
>> responsibility of userspace to do all the necessary syncing.
> 
> Sure, but nothing prohibits user-space to ignore the syncing thinking
> "It works anyway", testing those drivers where the syncing is a NOP. And
> when a driver that finally needs syncing is tested it's too late to fix
> all broken user-space.
> 
>>   I'm not
>> sure whether anyone in userspace really needs to map imported dma-bufs
>> in practice. Nevertheless, this use-case is broken and should be fixed
>> by either allowing to do the mapping or prohibiting it.
>>
> Then I'd vote for prohibiting it, at least for now. And for the future
> moving forward we could perhaps revisit the dma-buf need for syncing,
> requiring those drivers that actually need it to implement emulated
> coherent memory which can be done not too inefficiently (vmwgfx being
> one example).

Alright, I'll change it to prohibit the mapping. This indeed should be a
better option.
  

Am 30.06.22 um 01:06 schrieb Dmitry Osipenko:
> On 6/29/22 11:43, Thomas Hellström (Intel) wrote:
>> On 6/29/22 10:22, Dmitry Osipenko wrote:
>>> On 6/29/22 09:40, Thomas Hellström (Intel) wrote:
>>>> On 5/27/22 01:50, Dmitry Osipenko wrote:
>>>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
>>>>> handle imported dma-bufs properly, which results in mapping of
>>>>> something
>>>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a
>>>>> hard
>>>>> lockup when userspace writes to the memory mapping of a dma-buf that
>>>>> was
>>>>> imported into Tegra's DRM GEM.
>>>>>
>>>>> To fix this bug, move mapping of imported dma-bufs to
>>>>> drm_gem_mmap_obj().
>>>>> Now mmaping of imported dma-bufs works properly for all DRM drivers.
>>>> Same comment about Fixes: as in patch 1,
>>>>> Cc: stable@vger.kernel.org
>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>>>> ---
>>>>>     drivers/gpu/drm/drm_gem.c              | 3 +++
>>>>>     drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
>>>>>     drivers/gpu/drm/tegra/gem.c            | 4 ++++
>>>>>     3 files changed, 7 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>>>> index 86d670c71286..7c0b025508e4 100644
>>>>> --- a/drivers/gpu/drm/drm_gem.c
>>>>> +++ b/drivers/gpu/drm/drm_gem.c
>>>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj,
>>>>> unsigned long obj_size,
>>>>>         if (obj_size < vma->vm_end - vma->vm_start)
>>>>>             return -EINVAL;
>>>>>     +    if (obj->import_attach)
>>>>> +        return dma_buf_mmap(obj->dma_buf, vma, 0);
>>>> If we start enabling mmaping of imported dma-bufs on a majority of
>>>> drivers in this way, how do we ensure that user-space is not blindly
>>>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC
>>>> which is needed before and after cpu access of mmap'ed dma-bufs?
>>>>
>>>> I was under the impression (admittedly without looking) that the few
>>>> drivers that actually called into dma_buf_mmap() had some private
>>>> user-mode driver code in place that ensured this happened.
>>> Since it's a userspace who does the mapping, then it should be a
>>> responsibility of userspace to do all the necessary syncing.
>> Sure, but nothing prohibits user-space to ignore the syncing thinking
>> "It works anyway", testing those drivers where the syncing is a NOP. And
>> when a driver that finally needs syncing is tested it's too late to fix
>> all broken user-space.
>>
>>>    I'm not
>>> sure whether anyone in userspace really needs to map imported dma-bufs
>>> in practice. Nevertheless, this use-case is broken and should be fixed
>>> by either allowing to do the mapping or prohibiting it.
>>>
>> Then I'd vote for prohibiting it, at least for now. And for the future
>> moving forward we could perhaps revisit the dma-buf need for syncing,
>> requiring those drivers that actually need it to implement emulated
>> coherent memory which can be done not too inefficiently (vmwgfx being
>> one example).
> Alright, I'll change it to prohibit the mapping. This indeed should be a
> better option.

Oh, yes please. But I would expect that some people start screaming.

Over time I've got tons of TTM patches because people illegally tried to 
mmap() imported DMA-bufs in their driver.

Anyway this is probably the right thing to do and we can work on fixing 
the fallout later on.

Regards,
Christian.
  

On 7/4/22 15:33, Christian König wrote:
> Am 30.06.22 um 01:06 schrieb Dmitry Osipenko:
>> On 6/29/22 11:43, Thomas Hellström (Intel) wrote:
>>> On 6/29/22 10:22, Dmitry Osipenko wrote:
>>>> On 6/29/22 09:40, Thomas Hellström (Intel) wrote:
>>>>> On 5/27/22 01:50, Dmitry Osipenko wrote:
>>>>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't
>>>>>> handle imported dma-bufs properly, which results in mapping of
>>>>>> something
>>>>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a
>>>>>> hard
>>>>>> lockup when userspace writes to the memory mapping of a dma-buf that
>>>>>> was
>>>>>> imported into Tegra's DRM GEM.
>>>>>>
>>>>>> To fix this bug, move mapping of imported dma-bufs to
>>>>>> drm_gem_mmap_obj().
>>>>>> Now mmaping of imported dma-bufs works properly for all DRM drivers.
>>>>> Same comment about Fixes: as in patch 1,
>>>>>> Cc: stable@vger.kernel.org
>>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>>>>>> ---
>>>>>>     drivers/gpu/drm/drm_gem.c              | 3 +++
>>>>>>     drivers/gpu/drm/drm_gem_shmem_helper.c | 9 ---------
>>>>>>     drivers/gpu/drm/tegra/gem.c            | 4 ++++
>>>>>>     3 files changed, 7 insertions(+), 9 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>>>>>> index 86d670c71286..7c0b025508e4 100644
>>>>>> --- a/drivers/gpu/drm/drm_gem.c
>>>>>> +++ b/drivers/gpu/drm/drm_gem.c
>>>>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object
>>>>>> *obj,
>>>>>> unsigned long obj_size,
>>>>>>         if (obj_size < vma->vm_end - vma->vm_start)
>>>>>>             return -EINVAL;
>>>>>>     +    if (obj->import_attach)
>>>>>> +        return dma_buf_mmap(obj->dma_buf, vma, 0);
>>>>> If we start enabling mmaping of imported dma-bufs on a majority of
>>>>> drivers in this way, how do we ensure that user-space is not blindly
>>>>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC
>>>>> which is needed before and after cpu access of mmap'ed dma-bufs?
>>>>>
>>>>> I was under the impression (admittedly without looking) that the few
>>>>> drivers that actually called into dma_buf_mmap() had some private
>>>>> user-mode driver code in place that ensured this happened.
>>>> Since it's a userspace who does the mapping, then it should be a
>>>> responsibility of userspace to do all the necessary syncing.
>>> Sure, but nothing prohibits user-space to ignore the syncing thinking
>>> "It works anyway", testing those drivers where the syncing is a NOP. And
>>> when a driver that finally needs syncing is tested it's too late to fix
>>> all broken user-space.
>>>
>>>>    I'm not
>>>> sure whether anyone in userspace really needs to map imported dma-bufs
>>>> in practice. Nevertheless, this use-case is broken and should be fixed
>>>> by either allowing to do the mapping or prohibiting it.
>>>>
>>> Then I'd vote for prohibiting it, at least for now. And for the future
>>> moving forward we could perhaps revisit the dma-buf need for syncing,
>>> requiring those drivers that actually need it to implement emulated
>>> coherent memory which can be done not too inefficiently (vmwgfx being
>>> one example).
>> Alright, I'll change it to prohibit the mapping. This indeed should be a
>> better option.
> 
> Oh, yes please. But I would expect that some people start screaming.
> 
> Over time I've got tons of TTM patches because people illegally tried to
> mmap() imported DMA-bufs in their driver.
> 
> Anyway this is probably the right thing to do and we can work on fixing
> the fallout later on.

I already sent out the patch [1] that prohibits the mapping. Would be
great if you all could take a look and give a r-b, thanks in advance.

[1] https://patchwork.freedesktop.org/patch/492148/