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Date: Sat, 10 Mar 2018 07:27:21 -0800
From: Kees Cook <keescook@...omium.org>
To: Joao Moreira <jmoreira@...e.de>, Greg KH <gregkh@...uxfoundation.org>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
LKML <linux-kernel@...r.kernel.org>, Daniel Micay <danielmicay@...il.com>
Subject: Re: [PATCH] vgacon: fix function prototypes
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?
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
>
--
Kees Cook
Pixel Security
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