[PATCH 4.4 161/192] drm/msm: fix use of copy_from_user() while holding spinlock

[Greg Kroah-Hartman]

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

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

From: Rob Clark <robdcl...@gmail.com>

commit 89f82cbb0d5c0ab768c8d02914188aa2211cd2e3 upstream.

Use instead __copy_from_user_inatomic() and fallback to slow-path where
we drop and re-aquire the lock in case of fault.

Reported-by: Vaishali Thakkar <vaishali.thak...@oracle.com>
Signed-off-by: Rob Clark <robdcl...@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/gpu/drm/msm/msm_gem_submit.c |   27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -55,6 +55,14 @@ static struct msm_gem_submit *submit_cre
        return submit;
 }
 
+static inline unsigned long __must_check
+copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
+{
+       if (access_ok(VERIFY_READ, from, n))
+               return __copy_from_user_inatomic(to, from, n);
+       return -EFAULT;
+}
+
 static int submit_lookup_objects(struct msm_gem_submit *submit,
                struct drm_msm_gem_submit *args, struct drm_file *file)
 {
@@ -62,6 +70,7 @@ static int submit_lookup_objects(struct
        int ret = 0;
 
        spin_lock(&file->table_lock);
+       pagefault_disable();
 
        for (i = 0; i < args->nr_bos; i++) {
                struct drm_msm_gem_submit_bo submit_bo;
@@ -70,10 +79,15 @@ static int submit_lookup_objects(struct
                void __user *userptr =
                        to_user_ptr(args->bos + (i * sizeof(submit_bo)));
 
-               ret = copy_from_user(&submit_bo, userptr, sizeof(submit_bo));
-               if (ret) {
-                       ret = -EFAULT;
-                       goto out_unlock;
+               ret = copy_from_user_inatomic(&submit_bo, userptr, 
sizeof(submit_bo));
+               if (unlikely(ret)) {
+                       pagefault_enable();
+                       spin_unlock(&file->table_lock);
+                       ret = copy_from_user(&submit_bo, userptr, 
sizeof(submit_bo));
+                       if (ret)
+                               goto out;
+                       spin_lock(&file->table_lock);
+                       pagefault_disable();
                }
 
                if (submit_bo.flags & ~MSM_SUBMIT_BO_FLAGS) {
@@ -113,9 +127,12 @@ static int submit_lookup_objects(struct
        }
 
 out_unlock:
-       submit->nr_bos = i;
+       pagefault_enable();
        spin_unlock(&file->table_lock);
 
+out:
+       submit->nr_bos = i;
+
        return ret;
 }