drm/i915: Fix CFI violations in gt_sysfs

When booting with CONFIG_CFI_CLANG, there are numerous violations when
accessing the files under
/sys/devices/pci0000:00/0000:00:02.0/drm/card0/gt/gt0:

  $ cd /sys/devices/pci0000:00/0000:00:02.0/drm/card0/gt/gt0

  $ grep . *
  id:0
  punit_req_freq_mhz:350
  rc6_enable:1
  rc6_residency_ms:214934
  rps_act_freq_mhz:1300
  rps_boost_freq_mhz:1300
  rps_cur_freq_mhz:350
  rps_max_freq_mhz:1300
  rps_min_freq_mhz:350
  rps_RP0_freq_mhz:1300
  rps_RP1_freq_mhz:350
  rps_RPn_freq_mhz:350
  throttle_reason_pl1:0
  throttle_reason_pl2:0
  throttle_reason_pl4:0
  throttle_reason_prochot:0
  throttle_reason_ratl:0
  throttle_reason_status:0
  throttle_reason_thermal:0
  throttle_reason_vr_tdc:0
  throttle_reason_vr_thermalert:0

  $ sudo dmesg &| grep "CFI failure at"
  [  214.595903] CFI failure at kobj_attr_show+0x19/0x30 (target: id_show+0x0/0x70 [i915]; expected type: 0xc527b809)
  [  214.596064] CFI failure at kobj_attr_show+0x19/0x30 (target: punit_req_freq_mhz_show+0x0/0x40 [i915]; expected type: 0xc527b809)
  [  214.596407] CFI failure at kobj_attr_show+0x19/0x30 (target: rc6_enable_show+0x0/0x40 [i915]; expected type: 0xc527b809)
  [  214.596528] CFI failure at kobj_attr_show+0x19/0x30 (target: rc6_residency_ms_show+0x0/0x270 [i915]; expected type: 0xc527b809)
  [  214.596682] CFI failure at kobj_attr_show+0x19/0x30 (target: act_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.596792] CFI failure at kobj_attr_show+0x19/0x30 (target: boost_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.596893] CFI failure at kobj_attr_show+0x19/0x30 (target: cur_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.596996] CFI failure at kobj_attr_show+0x19/0x30 (target: max_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.597099] CFI failure at kobj_attr_show+0x19/0x30 (target: min_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.597198] CFI failure at kobj_attr_show+0x19/0x30 (target: RP0_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.597301] CFI failure at kobj_attr_show+0x19/0x30 (target: RP1_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.597405] CFI failure at kobj_attr_show+0x19/0x30 (target: RPn_freq_mhz_show+0x0/0xe0 [i915]; expected type: 0xc527b809)
  [  214.597538] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.597701] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.597836] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.597952] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.598071] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.598177] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.598307] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.598439] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)
  [  214.598542] CFI failure at kobj_attr_show+0x19/0x30 (target: throttle_reason_bool_show+0x0/0x50 [i915]; expected type: 0xc527b809)

With kCFI, indirect calls are validated against their expected type
versus actual type and failures occur when the two types do not match.
The ultimate issue is that these sysfs functions are expecting to be
called via dev_attr_show() but they may also be called via
kobj_attr_show(), as certain files are created under two different
kobjects that have two different sysfs_ops in intel_gt_sysfs_register(),
hence the warnings above. When accessing the gt_ files under
/sys/devices/pci0000:00/0000:00:02.0/drm/card0, which are using the same
sysfs functions, there are no violations, meaning the functions are
being called with the proper type.

To make everything work properly, adjust certain functions to match the
type of the ->show() and ->store() members in 'struct kobj_attribute'.
Add a macro to generate functions for that can be called via both
dev_attr_{show,store}() or kobj_attr_{show,store}() so that they can be
called through both kobject locations without violating kCFI and adjust
the attribute groups to account for this.

Link: https://github.com/ClangBuiltLinux/linux/issues/1716
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221013205909.1282545-1-nathan@kernel.org

1 files changed, 7 insertions, 8 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c b/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c
index d651ccd0ab20..9486dd3bed99 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_sysfs.c
@@ -22,11 +22,9 @@ bool is_object_gt(struct kobject *kobj)
 	return !strncmp(kobj->name, "gt", 2);
 }
 
-struct intel_gt *intel_gt_sysfs_get_drvdata(struct device *dev,
+struct intel_gt *intel_gt_sysfs_get_drvdata(struct kobject *kobj,
 					    const char *name)
 {
-	struct kobject *kobj = &dev->kobj;
-
 	/*
 	 * We are interested at knowing from where the interface
 	 * has been called, whether it's called from gt/ or from
@@ -38,6 +36,7 @@ struct intel_gt *intel_gt_sysfs_get_drvdata(struct device *dev,
 	 * "struct drm_i915_private *" type.
 	 */
 	if (!is_object_gt(kobj)) {
+		struct device *dev = kobj_to_dev(kobj);
 		struct drm_i915_private *i915 = kdev_minor_to_i915(dev);
 
 		return to_gt(i915);
@@ -51,18 +50,18 @@ static struct kobject *gt_get_parent_obj(struct intel_gt *gt)
 	return &gt->i915->drm.primary->kdev->kobj;
 }
 
-static ssize_t id_show(struct device *dev,
-		       struct device_attribute *attr,
+static ssize_t id_show(struct kobject *kobj,
+		       struct kobj_attribute *attr,
 		       char *buf)
 {
-	struct intel_gt *gt = intel_gt_sysfs_get_drvdata(dev, attr->attr.name);
+	struct intel_gt *gt = intel_gt_sysfs_get_drvdata(kobj, attr->attr.name);
 
 	return sysfs_emit(buf, "%u\n", gt->info.id);
 }
-static DEVICE_ATTR_RO(id);
+static struct kobj_attribute attr_id = __ATTR_RO(id);
 
 static struct attribute *id_attrs[] = {
-	&dev_attr_id.attr,
+	&attr_id.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(id);