From 1d23296c44671877ecb159fd1ac4087c7b67467f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= <thomas.hellstrom@linux.intel.com>
Date: Mon, 20 Jun 2022 14:36:59 +0200
Subject: drm/i915: Fix vm use-after-free in vma destruction
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Alt-commit: 1926a6b75954fc1a8b44d10bd0c67db957b78cf7
Alt-commit: 48da0f67c53eecd2594c302be6c8a665b7740eaf
Git-commit: 12058077b2e963d16d2d673d46233a7f46add7c9
Patch-mainline: v5.19-rc7
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225

In vma destruction, the following race may occur:

Thread 1:	    		  Thread 2:
i915_vma_destroy();

  ...
  list_del_init(vma->vm_link);
  ...
  mutex_unlock(vma->vm->mutex);
				  __i915_vm_release();
release_references();

And in release_reference() we dereference vma->vm to get to the
vm gt pointer, leading to a use-after free.

However, __i915_vm_release() grabs the vm->mutex so the vm won't be
destroyed before vma->vm->mutex is released, so extract the gt pointer
under the vm->mutex to avoid the vma->vm dereference in
release_references().

v2: Fix a typo in the commit message (Andi Shyti)

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/5944
Fixes: e1a7ab4fca0c ("drm/i915: Remove the vm open count")

Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.con>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220620123659.381772-1-thomas.hellstrom@linux.intel.com
(cherry picked from commit 1926a6b75954fc1a8b44d10bd0c67db957b78cf7)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/i915/i915_vma.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 0bffb70b3c5f..04d12f278f57 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1637,10 +1637,10 @@ static void force_unbind(struct i915_vma *vma)
 	GEM_BUG_ON(drm_mm_node_allocated(&vma->node));
 }
 
-static void release_references(struct i915_vma *vma, bool vm_ddestroy)
+static void release_references(struct i915_vma *vma, struct intel_gt *gt,
+			       bool vm_ddestroy)
 {
 	struct drm_i915_gem_object *obj = vma->obj;
-	struct intel_gt *gt = vma->vm->gt;
 
 	GEM_BUG_ON(i915_vma_is_active(vma));
 
@@ -1695,11 +1695,12 @@ void i915_vma_destroy_locked(struct i915_vma *vma)
 
 	force_unbind(vma);
 	list_del_init(&vma->vm_link);
-	release_references(vma, false);
+	release_references(vma, vma->vm->gt, false);
 }
 
 void i915_vma_destroy(struct i915_vma *vma)
 {
+	struct intel_gt *gt;
 	bool vm_ddestroy;
 
 	mutex_lock(&vma->vm->mutex);
@@ -1707,8 +1708,11 @@ void i915_vma_destroy(struct i915_vma *vma)
 	list_del_init(&vma->vm_link);
 	vm_ddestroy = vma->vm_ddestroy;
 	vma->vm_ddestroy = false;
+
+	/* vma->vm may be freed when releasing vma->vm->mutex. */
+	gt = vma->vm->gt;
 	mutex_unlock(&vma->vm->mutex);
-	release_references(vma, vm_ddestroy);
+	release_references(vma, gt, vm_ddestroy);
 }
 
 void i915_vma_parked(struct intel_gt *gt)
-- 
2.38.1