[PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Joonas Lahtinen]

Make sure the underlying VMA in the process address space is the
same as it was during vm_mmap to avoid applying WC to wrong VMA.

A more long-term solution would be to have vm_mmap_locked variant
in linux/mmap.h for when caller wants to hold mmap_sem for an
extended duration.

Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
Reported-by: Adam Zabrocki <adamza@microsoft.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.0+
Cc: Akash Goel <akash.goel@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Adam Zabrocki <adamza@microsoft.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 062c8395557c..f1d594a53978 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1680,6 +1680,15 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
 	return 0;
 }
 
+static inline bool
+match_gem_vma(struct vm_area_struct *vma, struct file *filp,
+	      unsigned long addr, unsigned long size)
+{
+	return vma && vma->vm_file == filp &&
+	       vma->vm_start == addr &&
+	       (vma->vm_end - vma->vm_start) == size;
+}
+
 /**
  * i915_gem_mmap_ioctl - Maps the contents of an object, returning the address
  *			 it is mapped to.
@@ -1738,7 +1747,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 			return -EINTR;
 		}
 		vma = find_vma(mm, addr);
-		if (vma)
+		if (match_gem_vma(vma, obj->base.filp, addr, args->size))
 			vma->vm_page_prot =
 				pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
 		else
-- 
2.17.2

[PATCH 2/2] drm/i915: Handle vm_mmap error during I915_GEM_MMAP ioctl with WC set

[Joonas Lahtinen]

Add err goto label and use it when VMA can't be established or changes
underneath.

Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
Reported-by: Adam Zabrocki <adamza@microsoft.com>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.0+
Cc: Akash Goel <akash.goel@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Adam Zabrocki <adamza@microsoft.com>
---
 drivers/gpu/drm/i915/i915_gem.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f1d594a53978..97cbc0e27e3e 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1738,6 +1738,9 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 	addr = vm_mmap(obj->base.filp, 0, args->size,
 		       PROT_READ | PROT_WRITE, MAP_SHARED,
 		       args->offset);
+	if (IS_ERR((void *)addr))
+		goto err;
+
 	if (args->flags & I915_MMAP_WC) {
 		struct mm_struct *mm = current->mm;
 		struct vm_area_struct *vma;
@@ -1753,17 +1756,22 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 		else
 			addr = -ENOMEM;
 		up_write(&mm->mmap_sem);
+		if (IS_ERR((void *)addr))
+			goto err;
 
 		/* This may race, but that's ok, it only gets set */
 		WRITE_ONCE(obj->frontbuffer_ggtt_origin, ORIGIN_CPU);
 	}
 	i915_gem_object_put(obj);
-	if (IS_ERR((void *)addr))
-		return addr;
 
 	args->addr_ptr = (uint64_t) addr;
 
 	return 0;
+
+err:
+	i915_gem_object_put(obj);
+
+	return addr;
 }
 
 static unsigned int tile_row_pages(const struct drm_i915_gem_object *obj)
-- 
2.17.2

Re: [PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Chris Wilson]

Quoting Joonas Lahtinen (2019-01-07 08:56:55)
> Make sure the underlying VMA in the process address space is the
> same as it was during vm_mmap to avoid applying WC to wrong VMA.
> 
> A more long-term solution would be to have vm_mmap_locked variant
> in linux/mmap.h for when caller wants to hold mmap_sem for an
> extended duration.
> 
> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 062c8395557c..f1d594a53978 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1680,6 +1680,15 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
>         return 0;
>  }
>  
> +static inline bool
> +match_gem_vma(struct vm_area_struct *vma, struct file *filp,
> +             unsigned long addr, unsigned long size)

With the exception of there isn't anything gem specific here,

> +{
> +       return vma && vma->vm_file == filp &&
> +              vma->vm_start == addr &&
> +              (vma->vm_end - vma->vm_start) == size;

and we can break this up into separate ifs with a forgiving compiler,

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

I still couldn't see an easy way of passing pgprot bits into do_mmap to
avoid the race entirely.
-Chris

Re: [PATCH 2/2] drm/i915: Handle vm_mmap error during I915_GEM_MMAP ioctl with WC set

[Chris Wilson]

Quoting Joonas Lahtinen (2019-01-07 08:56:56)
> Add err goto label and use it when VMA can't be established or changes
> underneath.
> 
> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")

Dubious. All it changes is one branch where the error is forced to
-ENOMEM.

> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index f1d594a53978..97cbc0e27e3e 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1738,6 +1738,9 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>         addr = vm_mmap(obj->base.filp, 0, args->size,
>                        PROT_READ | PROT_WRITE, MAP_SHARED,
>                        args->offset);
> +       if (IS_ERR((void *)addr))
> +               goto err;
> +
>         if (args->flags & I915_MMAP_WC) {
>                 struct mm_struct *mm = current->mm;
>                 struct vm_area_struct *vma;
> @@ -1753,17 +1756,22 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                 else
>                         addr = -ENOMEM;
>                 up_write(&mm->mmap_sem);
> +               if (IS_ERR((void *)addr))
> +                       goto err;

The issue still remains that we are returning having called vm_mmap and
leaving the vma intact. And we've established above that calling
vm_munmap() is a race.
-Chris

Re: [PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Tvrtko Ursulin]

On 07/01/2019 08:56, Joonas Lahtinen wrote:
> Make sure the underlying VMA in the process address space is the
> same as it was during vm_mmap to avoid applying WC to wrong VMA.
> 
> A more long-term solution would be to have vm_mmap_locked variant
> in linux/mmap.h for when caller wants to hold mmap_sem for an
> extended duration.
> 
> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 062c8395557c..f1d594a53978 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1680,6 +1680,15 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
>   	return 0;
>   }
>   
> +static inline bool
> +match_gem_vma(struct vm_area_struct *vma, struct file *filp,
> +	      unsigned long addr, unsigned long size)
> +{
> +	return vma && vma->vm_file == filp &&
> +	       vma->vm_start == addr &&
> +	       (vma->vm_end - vma->vm_start) == size;
> +}
> +
>   /**
>    * i915_gem_mmap_ioctl - Maps the contents of an object, returning the address
>    *			 it is mapped to.
> @@ -1738,7 +1747,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>   			return -EINTR;
>   		}
>   		vma = find_vma(mm, addr);
> -		if (vma)
> +		if (match_gem_vma(vma, obj->base.filp, addr, args->size))
>   			vma->vm_page_prot =
>   				pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
>   		else
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

Re: [PATCH 2/2] drm/i915: Handle vm_mmap error during I915_GEM_MMAP ioctl with WC set

[Tvrtko Ursulin]

On 07/01/2019 08:56, Joonas Lahtinen wrote:
> Add err goto label and use it when VMA can't be established or changes
> underneath.
> 
> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 12 ++++++++++--
>   1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index f1d594a53978..97cbc0e27e3e 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1738,6 +1738,9 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>   	addr = vm_mmap(obj->base.filp, 0, args->size,
>   		       PROT_READ | PROT_WRITE, MAP_SHARED,
>   		       args->offset);
> +	if (IS_ERR((void *)addr))
> +		goto err;
> +
>   	if (args->flags & I915_MMAP_WC) {
>   		struct mm_struct *mm = current->mm;
>   		struct vm_area_struct *vma;
> @@ -1753,17 +1756,22 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>   		else
>   			addr = -ENOMEM;
>   		up_write(&mm->mmap_sem);
> +		if (IS_ERR((void *)addr))
> +			goto err;
>   
>   		/* This may race, but that's ok, it only gets set */
>   		WRITE_ONCE(obj->frontbuffer_ggtt_origin, ORIGIN_CPU);
>   	}
>   	i915_gem_object_put(obj);
> -	if (IS_ERR((void *)addr))
> -		return addr;
>   
>   	args->addr_ptr = (uint64_t) addr;
>   
>   	return 0;
> +
> +err:
> +	i915_gem_object_put(obj);
> +
> +	return addr;
>   }
>   
>   static unsigned int tile_row_pages(const struct drm_i915_gem_object *obj)
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

Re: [PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Joonas Lahtinen]

Quoting Joonas Lahtinen (2019-01-07 10:56:55)
> Make sure the underlying VMA in the process address space is the
> same as it was during vm_mmap to avoid applying WC to wrong VMA.
> 
> A more long-term solution would be to have vm_mmap_locked variant
> in linux/mmap.h for when caller wants to hold mmap_sem for an
> extended duration.

These are now merged to drm-tip, and will head to 5.1 and then
to stable kernels.

Thanks for the report and reviews!

Regards, Joonas

> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 062c8395557c..f1d594a53978 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1680,6 +1680,15 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
>         return 0;
>  }
>  
> +static inline bool
> +match_gem_vma(struct vm_area_struct *vma, struct file *filp,
> +             unsigned long addr, unsigned long size)
> +{
> +       return vma && vma->vm_file == filp &&
> +              vma->vm_start == addr &&
> +              (vma->vm_end - vma->vm_start) == size;
> +}
> +
>  /**
>   * i915_gem_mmap_ioctl - Maps the contents of an object, returning the address
>   *                      it is mapped to.
> @@ -1738,7 +1747,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                         return -EINTR;
>                 }
>                 vma = find_vma(mm, addr);
> -               if (vma)
> +               if (match_gem_vma(vma, obj->base.filp, addr, args->size))
>                         vma->vm_page_prot =
>                                 pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
>                 else
> -- 
> 2.17.2
> 

RE: [PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

[Adam Zabrocki]

Thanks for the patch for both issues!

Best regards,
Adam

-----Original Message-----
From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> 
Sent: Thursday, February 7, 2019 5:39 AM
To: Intel graphics driver community testing & development <intel-gfx@lists.freedesktop.org>
Cc: stable@vger.kernel.org; Akash Goel <akash.goel@intel.com>; Chris Wilson <chris@chris-wilson.co.uk>; Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>; Adam Zabrocki <adamza@microsoft.com>
Subject: Re: [PATCH 1/2] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

Quoting Joonas Lahtinen (2019-01-07 10:56:55)
> Make sure the underlying VMA in the process address space is the same 
> as it was during vm_mmap to avoid applying WC to wrong VMA.
> 
> A more long-term solution would be to have vm_mmap_locked variant in 
> linux/mmap.h for when caller wants to hold mmap_sem for an extended 
> duration.

These are now merged to drm-tip, and will head to 5.1 and then to stable kernels.

Thanks for the report and reviews!

Regards, Joonas

> Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user 
> mappings for objects")
> Reported-by: Adam Zabrocki <adamza@microsoft.com>
> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: <stable@vger.kernel.org> # v4.0+
> Cc: Akash Goel <akash.goel@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Adam Zabrocki <adamza@microsoft.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c 
> b/drivers/gpu/drm/i915/i915_gem.c index 062c8395557c..f1d594a53978 
> 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1680,6 +1680,15 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
>         return 0;
>  }
>  
> +static inline bool
> +match_gem_vma(struct vm_area_struct *vma, struct file *filp,
> +             unsigned long addr, unsigned long size) {
> +       return vma && vma->vm_file == filp &&
> +              vma->vm_start == addr &&
> +              (vma->vm_end - vma->vm_start) == size; }
> +
>  /**
>   * i915_gem_mmap_ioctl - Maps the contents of an object, returning the address
>   *                      it is mapped to.
> @@ -1738,7 +1747,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
>                         return -EINTR;
>                 }
>                 vma = find_vma(mm, addr);
> -               if (vma)
> +               if (match_gem_vma(vma, obj->base.filp, addr, 
> + args->size))
>                         vma->vm_page_prot =
>                                 pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
>                 else
> --
> 2.17.2
>