linux-kernel - Re: [PATCH] vgacon: fix function prototypes

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Message-id: <4831767.IeJWIvYDSU@amdc3058>
Date:   Mon, 12 Mar 2018 15:06:12 +0100
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Joao Moreira <jmoreira@...e.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Micay <danielmicay@...il.com>,
        linux-fbdev@...r.kernel.org
Subject: Re: [PATCH] vgacon: fix function prototypes


Hi,

On Saturday, March 10, 2018 07:27:21 AM Kees Cook wrote:
> On Fri, Mar 9, 2018 at 10:40 PM, Joao Moreira <jmoreira@...e.de> wrote:
> > It is possible to indirectly invoke functions with prototypes that do not
> > match those of the respectively used function pointers by using void types.
> > Despite widely used as a feature for relaxing function invocation, this
> > should be avoided when possible as it may prevent the use of heuristics
> > such as prototype matching-based Control-Flow Integrity, which can be used
> > to prevent ROP-based attacks.
> >
> > Given the above, the current efforts to improve the Linux security, and the
> > upcoming kernel support to compilers with CFI features, fix prototypes in
> > vgacon console driver.
> >
> > Another similar fix can be seen in [1].
> >
> > [1] https://android-review.googlesource.com/c/kernel/common/+/602010
> >
> > Signed-off-by:  João Moreira <jmoreira@...e.de>
> 
> Whoops, I missed this one. :) Thanks! Greg, do you need this resent
> directly to you?

I would prefer for drivers/video/console/ changes to go through
fbdev tree (like suggested by scripts/get_maintainers.pl)..

However since Greg has already merged your CFI patches:

Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>

> Acked-by: Kees Cook <keescook@...omium.org>
> 
> -Kees
> 
> > ---
> >  drivers/video/console/vgacon.c | 18 +++++++++++++-----
> >  1 file changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> > index a17ba1465815..f00b630f6839 100644
> > --- a/drivers/video/console/vgacon.c
> > +++ b/drivers/video/console/vgacon.c
> > @@ -1407,21 +1407,29 @@ static bool vgacon_scroll(struct vc_data *c, unsigned int t, unsigned int b,
> >   *  The console `switch' structure for the VGA based console
> >   */
> >
> > -static int vgacon_dummy(struct vc_data *c)
> > +static int vgacon_clear(struct vc_data *c)
> >  {
> >         return 0;
> >  }
> >
> > -#define DUMMY (void *) vgacon_dummy
> > +static void vgacon_putc(struct vc_data *c, int a, int b, int d)
> > +{
> > +       return;
> > +}
> > +
> > +static void vgacon_putcs(struct vc_data *c, ushort *s, int a, int b, int d)
> > +{
> > +       return;
> > +}
> >
> >  const struct consw vga_con = {
> >         .owner = THIS_MODULE,
> >         .con_startup = vgacon_startup,
> >         .con_init = vgacon_init,
> >         .con_deinit = vgacon_deinit,
> > -       .con_clear = DUMMY,
> > -       .con_putc = DUMMY,
> > -       .con_putcs = DUMMY,
> > +       .con_clear = vgacon_clear,
> > +       .con_putc = vgacon_putc,
> > +       .con_putcs = vgacon_putcs,
> >         .con_cursor = vgacon_cursor,
> >         .con_scroll = vgacon_scroll,
> >         .con_switch = vgacon_switch,
> > --
> > 2.13.6

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics