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    Subject[PATCH 4.14 216/315] qemu_fw_cfg: Make fw_cfg_rev_attr a proper kobj_attribute
    Date
    From: Nathan Chancellor <nathan@kernel.org>

    commit fca41af18e10318e4de090db47d9fa7169e1bf2f upstream.

    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>
    Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
    Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
    Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
    Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
    Signed-off-by: Kees Cook <keescook@chromium.org>
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20210211194258.4137998-1-nathan@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/firmware/qemu_fw_cfg.c | 8 +++-----
    1 file changed, 3 insertions(+), 5 deletions(-)

    --- a/drivers/firmware/qemu_fw_cfg.c
    +++ b/drivers/firmware/qemu_fw_cfg.c
    @@ -192,15 +192,13 @@ static int fw_cfg_do_platform_probe(stru
    /* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
    static u32 fw_cfg_rev;

    -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,
    };

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