[PATCH] drm/nouveau: Fix out-of-bounds access when deferencing MMU type

[Thomas Zimmermann]

The value of struct drm_device.ttm.type_vram can become -1 for unknown
types of memory (see nouveau_ttm_init()). This leads to an out-of-bounds
error when accessing struct nvif_mmu.type[]:

  [   18.304116] ==================================================================
  [   18.311649] BUG: KASAN: slab-out-of-bounds in nouveau_ttm_io_mem_reserve+0x17a/0x7e0 [nouveau]
  [   18.320415] Read of size 1 at addr ffff88810ffac1fe by task systemd-udevd/342
  [   18.327681]
  [   18.329208] CPU: 1 PID: 342 Comm: systemd-udevd Tainted: G            E     5.10.0-rc2-1-default+ #581
  [   18.338681] Hardware name: Dell Inc. OptiPlex 9020/0N4YC8, BIOS A24 10/24/2018
  [   18.346032] Call Trace:
  [   18.348536]  dump_stack+0xae/0xe5
  [   18.351919]  print_address_description.constprop.0+0x17/0xf0
  [   18.357787]  ? nouveau_ttm_io_mem_reserve+0x17a/0x7e0 [nouveau]
  [   18.363818]  __kasan_report.cold+0x20/0x38
  [   18.368099]  ? nouveau_ttm_io_mem_reserve+0x17a/0x7e0 [nouveau]
  [   18.374133]  kasan_report+0x3a/0x50
  [   18.377789]  nouveau_ttm_io_mem_reserve+0x17a/0x7e0 [nouveau]
  <...>
  [   18.767690] Allocated by task 342:
  [   18.773087]  kasan_save_stack+0x1b/0x40
  [   18.778890]  __kasan_kmalloc.constprop.0+0xbf/0xd0
  [   18.785646]  __kmalloc_track_caller+0x1be/0x390
  [   18.792165]  kstrdup_const+0x46/0x70
  [   18.797686]  kobject_set_name_vargs+0x2f/0xb0
  [   18.803992]  kobject_init_and_add+0x9d/0xf0
  [   18.810117]  ttm_mem_global_init+0x12c/0x210 [ttm]
  [   18.816853]  ttm_bo_global_init+0x4a/0x160 [ttm]
  [   18.823420]  ttm_bo_device_init+0x39/0x220 [ttm]
  [   18.830046]  nouveau_ttm_init+0x2c3/0x830 [nouveau]
  [   18.836929]  nouveau_drm_device_init+0x1b4/0x3f0 [nouveau]
  <...>
  [   19.105336] ==================================================================

Fix this error, by not using type_vram as an index if it's negative.
Assume default values instead.

The error was seen on Nvidia G72 hardware.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Fixes: 1cf65c45183a ("drm/ttm: add caching state to ttm_bus_placement")
Cc: Christian König <christian.koenig at amd.com>
Cc: Michael J. Ruhl <michael.j.ruhl at intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <mripard at kernel.org>
Cc: Thomas Zimmermann <tzimmermann at suse.de>
Cc: David Airlie <airlied at linux.ie>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: Ben Skeggs <bskeggs at redhat.com>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: "Christian König" <christian.koenig at amd.com>
Cc: VMware Graphics <linux-graphics-maintainer at vmware.com>
Cc: Roland Scheidegger <sroland at vmware.com>
Cc: Huang Rui <ray.huang at amd.com>
Cc: Felix Kuehling <Felix.Kuehling at amd.com>
Cc: Hawking Zhang <Hawking.Zhang at amd.com>
Cc: Jason Gunthorpe <jgg at ziepe.ca>
Cc: Likun Gao <Likun.Gao at amd.com>
Cc: dri-devel at lists.freedesktop.org
Cc: nouveau at lists.freedesktop.org
Cc: virtualization at lists.linux-foundation.org
Cc: spice-devel at lists.freedesktop.org
Cc: amd-gfx at lists.freedesktop.org
---
 drivers/gpu/drm/nouveau/nouveau_bo.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
index 8133377d865d..fe15299d417e 100644
--- a/drivers/gpu/drm/nouveau/nouveau_bo.c
+++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
@@ -1142,9 +1142,12 @@ nouveau_ttm_io_mem_reserve(struct ttm_bo_device *bdev, struct ttm_resource *reg)
 	struct nvkm_device *device = nvxx_device(&drm->client.device);
 	struct nouveau_mem *mem = nouveau_mem(reg);
 	struct nvif_mmu *mmu = &drm->client.mmu;
-	const u8 type = mmu->type[drm->ttm.type_vram].type;
+	u8 type = 0;
 	int ret;
 
+	if (drm->ttm.type_vram >= 0)
+		type = mmu->type[drm->ttm.type_vram].type;
+
 	mutex_lock(&drm->ttm.io_reserve_mutex);
 retry:
 	switch (reg->mem_type) {
-- 
2.29.2