drm/msm: protect against faults from copy_from_user() in submit ioctl

commit d78d383ab354b0b9e1d23404ae0d9fbdeb9aa035 upstream.

An evil userspace could try to cause deadlock by passing an unfaulted-in
GEM bo as submit->bos (or submit->cmds) table.  Which will trigger
msm_gem_fault() while we already hold struct_mutex.  See:

https://github.com/freedreno/msmtest/blob/master/evilsubmittest.c

Signed-off-by: Rob Clark <robdclark@gmail.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
index 8a2c5fd0893e07f824b46e2d2d7528e96eca2ace..cb4a95b75dd727a5e20799526989ea74fecc07bb 100644 (file)
--- a/drivers/gpu/drm/msm/msm_drv.h
+++ b/drivers/gpu/drm/msm/msm_drv.h
@@ -124,6 +124,12 @@ struct msm_drm_private {
                 */
                struct drm_mm mm;
        } vram;
+
+       /* task holding struct_mutex.. currently only used in submit path
+        * to detect and reject faults from copy_from_user() for submit
+        * ioctl.
+        */
+       struct task_struct *struct_mutex_task;
 };
 
 struct msm_format {

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 690d7e7b6d1e8296891dde245d871850b0631715..f611b079a360c20023e16ec92e87be0b6593c68c 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -188,11 +188,20 @@ int msm_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
        struct drm_gem_object *obj = vma->vm_private_data;
        struct drm_device *dev = obj->dev;
+       struct msm_drm_private *priv = dev->dev_private;
        struct page **pages;
        unsigned long pfn;
        pgoff_t pgoff;
        int ret;
 
+       /* This should only happen if userspace tries to pass a mmap'd
+        * but unfaulted gem bo vaddr into submit ioctl, triggering
+        * a page fault while struct_mutex is already held.  This is
+        * not a valid use-case so just bail.
+        */
+       if (priv->struct_mutex_task == current)
+               return VM_FAULT_SIGBUS;
+
        /* Make sure we don't parallel update on a fault, nor move or remove
         * something from beneath our feet
         */

diff --git a/drivers/gpu/drm/msm/msm_gem_submit.c b/drivers/gpu/drm/msm/msm_gem_submit.c
index 0c0eacd9dd840a1f2a05afb080d272e46a6ce66b..0579511631268acb71be8276bf819dbed598a902 100644 (file)
--- a/drivers/gpu/drm/msm/msm_gem_submit.c
+++ b/drivers/gpu/drm/msm/msm_gem_submit.c
@@ -360,6 +360,8 @@ int msm_ioctl_gem_submit(struct drm_device *dev, void *data,
        if (ret)
                return ret;
 
+       priv->struct_mutex_task = current;
+
        submit = submit_create(dev, gpu, args->nr_bos);
        if (!submit) {
                ret = -ENOMEM;
@@ -442,6 +444,7 @@ out:
        if (submit)
                submit_cleanup(submit, !!ret);
 out_unlock:
+       priv->struct_mutex_task = NULL;
        mutex_unlock(&dev->struct_mutex);
        return ret;
 }