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    SubjectRe: [PATCH] qemu_fw_cfg: Make fw_cfg_rev_attr a proper kobj_attribute
    On Thu, Feb 11, 2021 at 12:42:58PM -0700, 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>

    Ah, nice, yes.

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

    Michael, are you able to take this? I can snag it if needed.

    -Kees

    > ---
    > 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
    >

    --
    Kees Cook

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