[PATCH] drm/i915: Fix CFI violation with show_dynamic_id()

From: Nathan Chancellor <nathan@kernel.org>
To: Jani Nikula <jani.nikula@linux.intel.com>,
	Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@intel.com>,
	Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Tom Rix <trix@redhat.com>,
	intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
	patches@lists.linux.dev, Nathan Chancellor <nathan@kernel.org>
Subject: [PATCH] drm/i915: Fix CFI violation with show_dynamic_id()
Date: Thu, 12 May 2022 14:17:04 -0700	[thread overview]
Message-ID: <20220512211704.3158759-1-nathan@kernel.org> (raw)

When an attribute group is created with sysfs_create_group(), the
->sysfs_ops() callback is set to kobj_sysfs_ops, which sets the ->show()
callback to kobj_attr_show(). kobj_attr_show() uses container_of() to
get the ->show() callback from the attribute it was passed, meaning the
->show() callback needs to be the same type as the ->show() callback in
'struct kobj_attribute'.

However, show_dynamic_id() has the type of the ->show() callback in
'struct device_attribute', which causes a CFI violation when opening the
'id' sysfs node under drm/card0/metrics. This happens to work because
the layout of 'struct kobj_attribute' and 'struct device_attribute' are
the same, so the container_of() cast happens to allow the ->show()
callback to still work.

Change the type of show_dynamic_id() to match the ->show() callback in
'struct kobj_attributes' and update the type of sysfs_metric_id to
match, which resolves the CFI violation.

Fixes: f89823c21224 ("drm/i915/perf: Implement I915_PERF_ADD/REMOVE_CONFIG interface")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 drivers/gpu/drm/i915/i915_perf.c       | 4 ++--
 drivers/gpu/drm/i915/i915_perf_types.h | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 0a9c3fcc09b1..1577ab6754db 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -4050,8 +4050,8 @@ static struct i915_oa_reg *alloc_oa_regs(struct i915_perf *perf,
 	return ERR_PTR(err);
 }
 
-static ssize_t show_dynamic_id(struct device *dev,
-			       struct device_attribute *attr,
+static ssize_t show_dynamic_id(struct kobject *kobj,
+			       struct kobj_attribute *attr,
 			       char *buf)
 {
 	struct i915_oa_config *oa_config =
diff --git a/drivers/gpu/drm/i915/i915_perf_types.h b/drivers/gpu/drm/i915/i915_perf_types.h
index 473a3c0544bb..05cb9a335a97 100644
--- a/drivers/gpu/drm/i915/i915_perf_types.h
+++ b/drivers/gpu/drm/i915/i915_perf_types.h
@@ -55,7 +55,7 @@ struct i915_oa_config {
 
 	struct attribute_group sysfs_metric;
 	struct attribute *attrs[2];
-	struct device_attribute sysfs_metric_id;
+	struct kobj_attribute sysfs_metric_id;
 
 	struct kref ref;
 	struct rcu_head rcu;

base-commit: 7ecc3cc8a7b39f08eee9aea7b718187583342a70
-- 
2.36.1

