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

From: Kees Cook <keescook@chromium.org>
To: Nathan Chancellor <nathan@kernel.org>,
	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: Tom Rix <trix@redhat.com>,
	intel-gfx@lists.freedesktop.org, llvm@lists.linux.dev,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	patches@lists.linux.dev, Sami Tolvanen <samitolvanen@google.com>
Subject: Re: [PATCH] drm/i915: Fix CFI violation with show_dynamic_id()
Date: Thu, 12 May 2022 14:30:17 -0700	[thread overview]
Message-ID: <DEB6A9AC-845E-4656-A596-E6341D3C287F@chromium.org> (raw)
In-Reply-To: <20220512211704.3158759-1-nathan@kernel.org>

On May 12, 2022 2:17:04 PM PDT, Nathan Chancellor <nathan@kernel.org> wrote:
>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>

This matches my own investigation into the error. Thanks for putting the patch together! :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook