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Subject[PATCH 4.19 84/85] drm/i915: Prevent a race during I915_GEM_MMAP ioctl with WC set
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

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.

v2:
- Refactor the compare function

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>
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 5c4604e757ba9b193b09768d75a7d2105a5b883f)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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
@@ -1821,6 +1821,16 @@ 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.
@@ -1879,7 +1889,7 @@ 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 =
pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
else

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