[PATCH 4.20 92/92] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set

From: Greg Kroah-Hartman
Date: Mon Feb 18 2019 - 08:49:47 EST

4.20-stable review patch. If anyone has any objections, please let me know.


From: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>

commit 2e7bd10e05afb866b5fb13eda25095c35d7a27cc upstream.

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.

- Refactor the compare function

Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user mappings for objects")
Reported-by: Adam Zabrocki <adamza@xxxxxxxxxxxxx>
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.0+
Cc: Akash Goel <akash.goel@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: Adam Zabrocki <adamza@xxxxxxxxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20190207085454.10598-1-joonas.lahtinen@xxxxxxxxxxxxxxx
(cherry picked from commit 5c4604e757ba9b193b09768d75a7d2105a5b883f)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

drivers/gpu/drm/i915/i915_gem.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1826,6 +1826,16 @@ i915_gem_sw_finish_ioctl(struct drm_devi
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.
@@ -1884,7 +1894,7 @@ i915_gem_mmap_ioctl(struct drm_device *d
return -EINTR;
vma = find_vma(mm, addr);
- if (vma)
+ if (vma && __vma_matches(vma, obj->base.filp, addr, args->size))
vma->vm_page_prot =