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Subject[PATCH 3.16 229/346] drm/msm: protect against faults from copy_from_user() in submit ioctl
3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Rob Clark <robdclark@gmail.com>

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>
---
drivers/gpu/drm/msm/msm_drv.h | 6 ++++++
drivers/gpu/drm/msm/msm_gem.c | 9 +++++++++
drivers/gpu/drm/msm/msm_gem_submit.c | 3 +++
3 files changed, 18 insertions(+)

--- 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 {
--- 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
{
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
*/
--- 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_devi
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;
}
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