diff mbox series

[v4,1/4] dma-buf: Require VM_PFNMAP vma for mmap

Message ID 20210713205153.1896059-2-daniel.vetter@ffwll.ch (mailing list archive)
State New, archived
Headers show
Series shmem helpers for vgem | expand

Commit Message

Daniel Vetter July 13, 2021, 8:51 p.m. UTC
tldr; DMA buffers aren't normal memory, expecting that you can use
them like that (like calling get_user_pages works, or that they're
accounting like any other normal memory) cannot be guaranteed.

Since some userspace only runs on integrated devices, where all
buffers are actually all resident system memory, there's a huge
temptation to assume that a struct page is always present and useable
like for any more pagecache backed mmap. This has the potential to
result in a uapi nightmare.

To stop this gap require that DMA buffer mmaps are VM_PFNMAP, which
blocks get_user_pages and all the other struct page based
infrastructure for everyone. In spirit this is the uapi counterpart to
the kernel-internal CONFIG_DMABUF_DEBUG.

Motivated by a recent patch which wanted to swich the system dma-buf
heap to vm_insert_page instead of vm_insert_pfn.

v2:

Jason brought up that we also want to guarantee that all ptes have the
pte_special flag set, to catch fast get_user_pages (on architectures
that support this). Allowing VM_MIXEDMAP (like VM_SPECIAL does) would
still allow vm_insert_page, but limiting to VM_PFNMAP will catch that.

From auditing the various functions to insert pfn pte entires
(vm_insert_pfn_prot, remap_pfn_range and all it's callers like
dma_mmap_wc) it looks like VM_PFNMAP is already required anyway, so
this should be the correct flag to check for.

References: https://lore.kernel.org/lkml/CAKMK7uHi+mG0z0HUmNt13QCCvutuRVjpcR0NjRL12k-WbWzkRg@mail.gmail.com/
Acked-by: Christian König <christian.koenig@amd.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
--
Resending this so I can test the next two patches for vgem/shmem in
intel-gfx-ci. Last round failed somehow, but I can't repro that at all
locally here.

No immediate plans to merge this patch here since ttm isn't addressed
yet (and there we have the hugepte issue, for which I don't think we
have a clear consensus yet).
-Daniel
---
 drivers/dma-buf/dma-buf.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

Comments

Thomas Zimmermann July 23, 2021, 6:45 p.m. UTC | #1
Hi

Am 13.07.21 um 22:51 schrieb Daniel Vetter:
> tldr; DMA buffers aren't normal memory, expecting that you can use
> them like that (like calling get_user_pages works, or that they're
> accounting like any other normal memory) cannot be guaranteed.
> 
> Since some userspace only runs on integrated devices, where all
> buffers are actually all resident system memory, there's a huge
> temptation to assume that a struct page is always present and useable
> like for any more pagecache backed mmap. This has the potential to
> result in a uapi nightmare.
> 
> To stop this gap require that DMA buffer mmaps are VM_PFNMAP, which
> blocks get_user_pages and all the other struct page based
> infrastructure for everyone. In spirit this is the uapi counterpart to
> the kernel-internal CONFIG_DMABUF_DEBUG.
> 
> Motivated by a recent patch which wanted to swich the system dma-buf
> heap to vm_insert_page instead of vm_insert_pfn.
> 
> v2:
> 
> Jason brought up that we also want to guarantee that all ptes have the
> pte_special flag set, to catch fast get_user_pages (on architectures
> that support this). Allowing VM_MIXEDMAP (like VM_SPECIAL does) would
> still allow vm_insert_page, but limiting to VM_PFNMAP will catch that.
> 
>  From auditing the various functions to insert pfn pte entires
> (vm_insert_pfn_prot, remap_pfn_range and all it's callers like
> dma_mmap_wc) it looks like VM_PFNMAP is already required anyway, so
> this should be the correct flag to check for.
> 
> References: https://lore.kernel.org/lkml/CAKMK7uHi+mG0z0HUmNt13QCCvutuRVjpcR0NjRL12k-WbWzkRg@mail.gmail.com/
> Acked-by: Christian König <christian.koenig@amd.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: John Stultz <john.stultz@linaro.org>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: "Christian König" <christian.koenig@amd.com>
> Cc: linux-media@vger.kernel.org
> Cc: linaro-mm-sig@lists.linaro.org
> --
> Resending this so I can test the next two patches for vgem/shmem in
> intel-gfx-ci. Last round failed somehow, but I can't repro that at all
> locally here.
> 
> No immediate plans to merge this patch here since ttm isn't addressed
> yet (and there we have the hugepte issue, for which I don't think we
> have a clear consensus yet).
> -Daniel
> ---
>   drivers/dma-buf/dma-buf.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 510b42771974..65cbd7f0f16a 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -130,6 +130,7 @@ static struct file_system_type dma_buf_fs_type = {
>   static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
>   {
>   	struct dma_buf *dmabuf;
> +	int ret;
>   
>   	if (!is_dma_buf_file(file))
>   		return -EINVAL;
> @@ -145,7 +146,11 @@ static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
>   	    dmabuf->size >> PAGE_SHIFT)
>   		return -EINVAL;
>   
> -	return dmabuf->ops->mmap(dmabuf, vma);
> +	ret = dmabuf->ops->mmap(dmabuf, vma);
> +
> +	WARN_ON(!(vma->vm_flags & VM_PFNMAP));

Maybe change this to WARN_ON_ONCE(), so it doesn't fill up the kernel 
log. Same comment below.

For either version

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

Best regards
Thomas

> +
> +	return ret;
>   }
>   
>   static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
> @@ -1276,6 +1281,8 @@ EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
>   int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>   		 unsigned long pgoff)
>   {
> +	int ret;
> +
>   	if (WARN_ON(!dmabuf || !vma))
>   		return -EINVAL;
>   
> @@ -1296,7 +1303,11 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>   	vma_set_file(vma, dmabuf->file);
>   	vma->vm_pgoff = pgoff;
>   
> -	return dmabuf->ops->mmap(dmabuf, vma);
> +	ret = dmabuf->ops->mmap(dmabuf, vma);
> +
> +	WARN_ON(!(vma->vm_flags & VM_PFNMAP));
> +
> +	return ret;
>   }
>   EXPORT_SYMBOL_GPL(dma_buf_mmap);
>   
>
diff mbox series

Patch

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 510b42771974..65cbd7f0f16a 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -130,6 +130,7 @@  static struct file_system_type dma_buf_fs_type = {
 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 {
 	struct dma_buf *dmabuf;
+	int ret;
 
 	if (!is_dma_buf_file(file))
 		return -EINVAL;
@@ -145,7 +146,11 @@  static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 	    dmabuf->size >> PAGE_SHIFT)
 		return -EINVAL;
 
-	return dmabuf->ops->mmap(dmabuf, vma);
+	ret = dmabuf->ops->mmap(dmabuf, vma);
+
+	WARN_ON(!(vma->vm_flags & VM_PFNMAP));
+
+	return ret;
 }
 
 static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
@@ -1276,6 +1281,8 @@  EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
 int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 		 unsigned long pgoff)
 {
+	int ret;
+
 	if (WARN_ON(!dmabuf || !vma))
 		return -EINVAL;
 
@@ -1296,7 +1303,11 @@  int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
 	vma_set_file(vma, dmabuf->file);
 	vma->vm_pgoff = pgoff;
 
-	return dmabuf->ops->mmap(dmabuf, vma);
+	ret = dmabuf->ops->mmap(dmabuf, vma);
+
+	WARN_ON(!(vma->vm_flags & VM_PFNMAP));
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(dma_buf_mmap);