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References: <20210211194258.4137998-1-nathan@kernel.org>
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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 22 Feb 2021 11:02:34 -0800
Message-ID: <CAKwvOdkJfJ+LDspz04tsjd=55LxF5rgTOAXt0cPxTyCCUBqgBw@mail.gmail.com>
Subject: Re: [PATCH] qemu_fw_cfg: Make fw_cfg_rev_attr a proper kobj_attribute
To:     Gabriel Somlo <somlo@cmu.edu>,
        "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Sami Tolvanen <samitolvanen@google.com>,
        Kees Cook <keescook@chromium.org>, qemu-devel@nongnu.org,
        LKML <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Nathan Chancellor <nathan@kernel.org>
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Did this happen to get picked up already? EOM

On Thu, Feb 11, 2021 at 11:43 AM Nathan Chancellor <nathan@kernel.org> 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(-)
>
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 0078260fbabe..172c751a4f6c 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -299,15 +299,13 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev)
>         return 0;
>  }
>
> -static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
> +static ssize_t fw_cfg_showrev(struct kobject *k, struct kobj_attribute *a,
> +                             char *buf)
>  {
>         return sprintf(buf, "%u\n", fw_cfg_rev);
>  }
>
> -static const struct {
> -       struct attribute attr;
> -       ssize_t (*show)(struct kobject *k, struct attribute *a, char *buf);
> -} fw_cfg_rev_attr = {
> +static const struct kobj_attribute fw_cfg_rev_attr = {
>         .attr = { .name = "rev", .mode = S_IRUSR },
>         .show = fw_cfg_showrev,
>  };
>
> base-commit: 92bf22614b21a2706f4993b278017e437f7785b3
> --
> 2.30.1
>
> --
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-- 
Thanks,
~Nick Desaulniers