Patch "drm/ttm: fix use-after-free races in vm fault handling" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    drm/ttm: fix use-after-free races in vm fault handling

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     drm-ttm-fix-use-after-free-races-in-vm-fault-handling.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 3089c1df10e2931b1d72d2ffa7d86431084c86b3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= <nicolai.haehnle@amd.com>
Date: Sat, 18 Feb 2017 22:59:56 +0100
Subject: drm/ttm: fix use-after-free races in vm fault handling
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Content-Transfer-Encoding: 8bit

From: Nicolai Hähnle <nicolai.haehnle@amd.com>

commit 3089c1df10e2931b1d72d2ffa7d86431084c86b3 upstream.

The vm fault handler relies on the fact that the VMA owns a reference
to the BO. However, once mmap_sem is released, other tasks are free to
destroy the VMA, which can lead to the BO being freed. Fix two code
paths where that can happen, both related to vm fault retries.

Found via a lock debugging warning which flagged &bo->wu_mutex as
locked while being destroyed.

Fixes: cbe12e74ee4e ("drm/ttm: Allow vm fault retries")
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/gpu/drm/ttm/ttm_bo_vm.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -66,8 +66,11 @@ static int ttm_bo_vm_fault_idle(struct t
 		if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
 			goto out_unlock;
 
+		ttm_bo_reference(bo);
 		up_read(&vma->vm_mm->mmap_sem);
 		(void) ttm_bo_wait(bo, false, true, false);
+		ttm_bo_unreserve(bo);
+		ttm_bo_unref(&bo);
 		goto out_unlock;
 	}
 
@@ -114,8 +117,10 @@ static int ttm_bo_vm_fault(struct vm_are
 
 		if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) {
 			if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
+				ttm_bo_reference(bo);
 				up_read(&vma->vm_mm->mmap_sem);
 				(void) ttm_bo_wait_unreserved(bo);
+				ttm_bo_unref(&bo);
 			}
 
 			return VM_FAULT_RETRY;
@@ -160,6 +165,13 @@ static int ttm_bo_vm_fault(struct vm_are
 	ret = ttm_bo_vm_fault_idle(bo, vma, vmf);
 	if (unlikely(ret != 0)) {
 		retval = ret;
+
+		if (retval == VM_FAULT_RETRY &&
+		    !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
+			/* The BO has already been unreserved. */
+			return retval;
+		}
+
 		goto out_unlock;
 	}
 


Patches currently in stable-queue which might be from nicolai.haehnle@amd.com are

queue-4.4/drm-ttm-fix-use-after-free-races-in-vm-fault-handling.patch