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Date:   Mon, 22 Feb 2021 12:08:06 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     Gabriel Somlo <somlo@cmu.edu>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        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>
Subject: Re: [PATCH] qemu_fw_cfg: Make fw_cfg_rev_attr a proper kobj_attribute
Message-ID: <20210222190806.GA41637@24bbad8f3778>
References: <20210211194258.4137998-1-nathan@kernel.org>
 <CAKwvOdkJfJ+LDspz04tsjd=55LxF5rgTOAXt0cPxTyCCUBqgBw@mail.gmail.com>
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On Mon, Feb 22, 2021 at 11:02:34AM -0800, Nick Desaulniers wrote:
> Did this happen to get picked up already? EOM

I have not gotten an email saying it has been picked up nor does it
appear to be in -next.

Cheers,
Nathan

> 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
> >