[PATCH 1/3] drm: Hold mode_config.lock to prevent hotplug whilst setting up crtcs

Chris Wilson
2016-11-23T14:04:15Z

The fb_helper->connector_count is modified when a new connector is
constructed following a hotplug event (e.g. DP-MST). This causes trouble
for drm_setup_crtcs() and friends that assume that fb_helper is
constant:

[ 1250.872997] BUG: KASAN: slab-out-of-bounds in drm_setup_crtcs+0x320/0xf80 at addr ffff88074cdd2608
[ 1250.873020] Write of size 40 by task kworker/u8:3/480
[ 1250.873039] CPU: 2 PID: 480 Comm: kworker/u8:3 Tainted: G U 4.9.0-rc6+ #285
[ 1250.873043] Hardware name: /NUC6i3SYB, BIOS SYSKLi35.86A.0024.2015.1027.2142 10/27/2015
[ 1250.873050] Workqueue: events_unbound async_run_entry_fn
[ 1250.873056] ffff88070f9d78f0 ffffffff814b72aa ffff88074e40c5c0 ffff88074cdd2608
[ 1250.873067] ffff88070f9d7918 ffffffff8124ff3c ffff88070f9d79b0 ffff88074cdd2600
[ 1250.873079] ffff88074e40c5c0 ffff88070f9d79a0 ffffffff812501e4 0000000000000005
[ 1250.873090] Call Trace:
[ 1250.873099] [<ffffffff814b72aa>] dump_stack+0x67/0x9d
[ 1250.873106] [<ffffffff8124ff3c>] kasan_object_err+0x1c/0x70
[ 1250.873113] [<ffffffff812501e4>] kasan_report_error+0x204/0x4f0
[ 1250.873120] [<ffffffff81698df0>] ? drm_dev_printk+0x140/0x140
[ 1250.873127] [<ffffffff81250ac3>] kasan_report+0x53/0x60
[ 1250.873134] [<ffffffff81688b40>] ? drm_setup_crtcs+0x320/0xf80
[ 1250.873142] [<ffffffff8124f18e>] check_memory_region+0x13e/0x1a0
[ 1250.873147] [<ffffffff8124f5f3>] memset+0x23/0x40
[ 1250.873154] [<ffffffff81688b40>] drm_setup_crtcs+0x320/0xf80
[ 1250.873161] [<ffffffff810be7c5>] ? wake_up_q+0x45/0x80
[ 1250.873169] [<ffffffff81b0c180>] ? mutex_lock_nested+0x5a0/0x5a0
[ 1250.873176] [<ffffffff8168a0e6>] drm_fb_helper_initial_config+0x206/0x7a0
[ 1250.873183] [<ffffffff81689ee0>] ? drm_fb_helper_set_par+0x90/0x90
[ 1250.873303] [<ffffffffa0b68690>] ? intel_fbdev_fini+0x140/0x140 [i915]
[ 1250.873387] [<ffffffffa0b686b2>] intel_fbdev_initial_config+0x22/0x40 [i915]
[ 1250.873391] [<ffffffff810b50ff>] async_run_entry_fn+0x7f/0x270
[ 1250.873394] [<ffffffff810a64b0>] process_one_work+0x3d0/0x960
[ 1250.873398] [<ffffffff810a641d>] ? process_one_work+0x33d/0x960
[ 1250.873401] [<ffffffff810a60e0>] ? max_active_store+0xf0/0xf0
[ 1250.873406] [<ffffffff810f6f9d>] ? do_raw_spin_lock+0x10d/0x1a0
[ 1250.873413] [<ffffffff810a767d>] worker_thread+0x8d/0x840
[ 1250.873419] [<ffffffff810a75f0>] ? create_worker+0x2e0/0x2e0
[ 1250.873426] [<ffffffff810b0454>] kthread+0x194/0x1c0
[ 1250.873432] [<ffffffff810b02c0>] ? kthread_park+0x60/0x60
[ 1250.873438] [<ffffffff810f095d>] ? trace_hardirqs_on+0xd/0x10
[ 1250.873446] [<ffffffff810b02c0>] ? kthread_park+0x60/0x60
[ 1250.873453] [<ffffffff810b02c0>] ? kthread_park+0x60/0x60
[ 1250.873457] [<ffffffff81b12277>] ret_from_fork+0x27/0x40
[ 1250.873460] Object at ffff88074cdd2608, in cache kmalloc-32 size: 32

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98826
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
drivers/gpu/drm/drm_fb_helper.c | 73 ++++++++++++++++++++++-------------------
1 file changed, 40 insertions(+), 33 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 14547817566d..d13c85682891 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -97,6 +97,10 @@ static LIST_HEAD(kernel_fb_helper_list);
* mmap page writes.
*/

+#define drm_fb_helper_for_each_connector(fbh, i__) \
+ for (({lockdep_assert_held(&(fbh)->dev->mode_config.mutex); 1;}), \
+ i__ = 0; i__ < (fbh)->connector_count; i__++)
+
/**
* drm_fb_helper_single_add_all_connectors() - add all connectors to fbdev
* emulation helper
@@ -130,7 +134,7 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
mutex_unlock(&dev->mode_config.mutex);
return 0;
fail:
- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
struct drm_fb_helper_connector *fb_helper_connector =
fb_helper->connector_info[i];

@@ -565,7 +569,7 @@ static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
continue;

/* Walk the connectors & encoders on this fb turning them on/off */
- for (j = 0; j < fb_helper->connector_count; j++) {
+ drm_fb_helper_for_each_connector(fb_helper, j) {
connector = fb_helper->connector_info[j]->connector;
connector->funcs->dpms(connector, dpms_mode);
drm_object_property_set_value(&connector->base,
@@ -1469,7 +1473,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
int ret = 0;
int crtc_count = 0;
int i;
- struct fb_info *info;
struct drm_fb_helper_surface_size sizes;
int gamma_size = 0;

@@ -1485,7 +1488,7 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
sizes.surface_depth = sizes.surface_bpp = preferred_bpp;

/* first up get a count of crtcs now in use and new min/maxes width/heights */
- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
struct drm_fb_helper_connector *fb_helper_conn = fb_helper->connector_info[i];
struct drm_cmdline_mode *cmdline_mode;

@@ -1572,8 +1575,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
if (ret < 0)
return ret;

- info = fb_helper->fbdev;
-
/*
* Set the fb pointer - usually drm_setup_crtcs does this for hotplug
* events, but at init time drm_setup_crtcs needs to be called before
@@ -1585,20 +1586,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
if (fb_helper->crtc_info[i].mode_set.num_connectors)
fb_helper->crtc_info[i].mode_set.fb = fb_helper->fb;

-
- info->var.pixclock = 0;
- if (register_framebuffer(info) < 0)
- return -EINVAL;
-
- dev_info(fb_helper->dev->dev, "fb%d: %s frame buffer device\n",
- info->node, info->fix.id);
-
- if (list_empty(&kernel_fb_helper_list)) {
- register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
- }
-
- list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
-
return 0;
}

@@ -1730,7 +1717,7 @@ static int drm_fb_helper_probe_connector_modes(struct drm_fb_helper *fb_helper,
int count = 0;
int i;

- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
connector = fb_helper->connector_info[i]->connector;
count += connector->funcs->fill_modes(connector, maxX, maxY);
}
@@ -1830,7 +1817,7 @@ static void drm_enable_connectors(struct drm_fb_helper *fb_helper,
struct drm_connector *connector;
int i = 0;

- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
connector = fb_helper->connector_info[i]->connector;
enabled[i] = drm_connector_enabled(connector, true);
DRM_DEBUG_KMS("connector %d enabled? %s\n", connector->base.id,
@@ -1841,7 +1828,7 @@ static void drm_enable_connectors(struct drm_fb_helper *fb_helper,
if (any_enabled)
return;

- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
connector = fb_helper->connector_info[i]->connector;
enabled[i] = drm_connector_enabled(connector, false);
}
@@ -1862,7 +1849,7 @@ static bool drm_target_cloned(struct drm_fb_helper *fb_helper,
return false;

count = 0;
- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
if (enabled[i])
count++;
}
@@ -1873,7 +1860,7 @@ static bool drm_target_cloned(struct drm_fb_helper *fb_helper,

/* check the command line or if nothing common pick 1024x768 */
can_clone = true;
- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
if (!enabled[i])
continue;
fb_helper_conn = fb_helper->connector_info[i];
@@ -1899,8 +1886,7 @@ static bool drm_target_cloned(struct drm_fb_helper *fb_helper,
can_clone = true;
dmt_mode = drm_mode_find_dmt(fb_helper->dev, 1024, 768, 60, false);

- for (i = 0; i < fb_helper->connector_count; i++) {
-
+ drm_fb_helper_for_each_connector(fb_helper, i) {
if (!enabled[i])
continue;

@@ -1931,7 +1917,7 @@ static int drm_get_tile_offsets(struct drm_fb_helper *fb_helper,
int i;
int hoffset = 0, voffset = 0;

- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
fb_helper_conn = fb_helper->connector_info[i];
if (!fb_helper_conn->connector->has_tile)
continue;
@@ -1964,7 +1950,7 @@ static bool drm_target_preferred(struct drm_fb_helper *fb_helper,
int tile_pass = 0;
mask = (1 << fb_helper->connector_count) - 1;
retry:
- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
fb_helper_conn = fb_helper->connector_info[i];

if (conn_configured & (1 << i))
@@ -2127,6 +2113,9 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper)
width = dev->mode_config.max_width;
height = dev->mode_config.max_height;

+ /* prevent concurrent modification of connector_count by hotplug */
+ lockdep_assert_held(&fb_helper->dev->mode_config.mutex);
+
crtcs = kcalloc(fb_helper->connector_count,
sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
modes = kcalloc(fb_helper->connector_count,
@@ -2140,7 +2129,6 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper)
goto out;
}

-
drm_enable_connectors(fb_helper, enabled);

if (!(fb_helper->funcs->initial_config &&
@@ -2169,7 +2157,7 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper)
drm_fb_helper_modeset_release(fb_helper,
&fb_helper->crtc_info[i].mode_set);

- for (i = 0; i < fb_helper->connector_count; i++) {
+ drm_fb_helper_for_each_connector(fb_helper, i) {
struct drm_display_mode *mode = modes[i];
struct drm_fb_helper_crtc *fb_crtc = crtcs[i];
struct drm_fb_offset *offset = &offsets[i];
@@ -2246,7 +2234,9 @@ static void drm_setup_crtcs(struct drm_fb_helper *fb_helper)
int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
{
struct drm_device *dev = fb_helper->dev;
+ struct fb_info *info;
int count = 0;
+ int ret;

if (!drm_fbdev_emulation)
return 0;
@@ -2255,7 +2245,6 @@ int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
count = drm_fb_helper_probe_connector_modes(fb_helper,
dev->mode_config.max_width,
dev->mode_config.max_height);
- mutex_unlock(&dev->mode_config.mutex);
/*
* we shouldn't end up with no modes here.
*/
@@ -2263,8 +2252,26 @@ int drm_fb_helper_initial_config(struct drm_fb_helper *fb_helper, int bpp_sel)
dev_info(fb_helper->dev->dev, "No connectors reported connected with modes\n");

drm_setup_crtcs(fb_helper);
+ ret = drm_fb_helper_single_fb_probe(fb_helper, bpp_sel);
+ mutex_unlock(&dev->mode_config.mutex);
+ if (ret)
+ return ret;

- return drm_fb_helper_single_fb_probe(fb_helper, bpp_sel);
+ info = fb_helper->fbdev;
+ info->var.pixclock = 0;
+ ret = register_framebuffer(info);
+ if (ret < 0)
+ return ret;
+
+ dev_info(dev->dev, "fb%d: %s frame buffer device\n",
+ info->node, info->fix.id);
+
+ if (list_empty(&kernel_fb_helper_list))
+ register_sysrq_key('v', &sysrq_drm_fb_helper_restore_op);
+
+ list_add(&fb_helper->kernel_fb_list, &kernel_fb_helper_list);
+
+ return 0;
}
EXPORT_SYMBOL(drm_fb_helper_initial_config);

--
2.10.2