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Subject: Re: [PATCH] qemu_fw_cfg: Make fw_cfg_rev_attr a proper kobj_attribute
To:     Nathan Chancellor <nathan@kernel.org>,
        Gabriel Somlo <somlo@cmu.edu>,
        "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Kees Cook <keescook@chromium.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
        clang-built-linux@googlegroups.com,
        Sami Tolvanen <samitolvanen@google.com>
References: <20210211194258.4137998-1-nathan@kernel.org>
From:   =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <philmd@redhat.com>
Message-ID: <6ac57db8-3866-297a-dc37-87c565b51ee2@redhat.com>
Date:   Thu, 25 Feb 2021 11:41:58 +0100
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On 2/11/21 8:42 PM, Nathan Chancellor wrote:
> fw_cfg_showrev() is called by an indirect call in kobj_attr_show(),
> which violates clang's CFI checking because fw_cfg_showrev()'s second
> parameter is 'struct attribute', whereas the ->show() member of 'struct
> kobj_structure' expects the second parameter to be of type 'struct
> kobj_attribute'.
> 
> $ cat /sys/firmware/qemu_fw_cfg/rev
> 3
> 
> $ dmesg | grep "CFI failure"
> [   26.016832] CFI failure (target: fw_cfg_showrev+0x0/0x8):
> 
> Fix this by converting fw_cfg_rev_attr to 'struct kobj_attribute' where
> this would have been caught automatically by the incompatible pointer
> types compiler warning. Update fw_cfg_showrev() accordingly.
> 
> Fixes: 75f3e8e47f38 ("firmware: introduce sysfs driver for QEMU's fw_cfg device")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1299
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> ---
>  drivers/firmware/qemu_fw_cfg.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>