drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

jlahtine-intel · jnikula · commit 2e7bd10e05af · 2019-02-12T15:37:40.000+02:00
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. v2: - Refactor the compare function Fixes: 1816f92 ("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> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> #v1 Link: https://patchwork.freedesktop.org/patch/msgid/20190207085454.10598-1-joonas.lahtinen@linux.intel.com (cherry picked from commit 5c4604e) Signed-off-by: Jani Nikula <jani.nikula@intel.com>
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
@@ -1824,6 +1824,16 @@ i915_gem_sw_finish_ioctl(struct drm_device *dev, void *data,
 	return 0;
 }
 
+static inline bool
+__vma_matches(struct vm_area_struct *vma, struct file *filp,
+	      unsigned long addr, unsigned long size)
+{
+	if (vma->vm_file != filp)
+		return false;
+
+	return 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.
@@ -1882,7 +1892,7 @@ i915_gem_mmap_ioctl(struct drm_device *dev, void *data,
 			return -EINTR;
 		}
 		vma = find_vma(mm, addr);
-		if (vma)
+		if (vma && __vma_matches(vma, obj->base.filp, addr, args->size))
 			vma->vm_page_prot =
 				pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
 		else
