Re: [PATCH] ARM: orion: avoid VLA in orion_mpp_conf

[Kees Cook]

On Fri, Oct 5, 2018 at 9:15 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> Testing randconfig builds found an instance of a VLA that was
> missed when determining that we have removed them all:
>
> arch/arm/plat-orion/mpp.c: In function 'orion_mpp_conf':
> arch/arm/plat-orion/mpp.c:31:2: error: ISO C90 forbids variable length array 'mpp_ctrl' [-Werror=vla]

Ah! Thanks for catching this. It seems "allmodconfig" isn't quite "all". ;)

> This one is fairly straightforward: we know what all three
> callers are, and the maximum length is not very long.
>
> Fixes: 68664695ae57 ("Makefile: Globally enable VLA warning")
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  arch/arm/plat-orion/mpp.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/plat-orion/mpp.c b/arch/arm/plat-orion/mpp.c
> index 5b4ff9373c89..8a6880d528b6 100644
> --- a/arch/arm/plat-orion/mpp.c
> +++ b/arch/arm/plat-orion/mpp.c
> @@ -28,10 +28,15 @@ void __init orion_mpp_conf(unsigned int *mpp_list, unsigned int variant_mask,
>                            unsigned int mpp_max, void __iomem *dev_bus)

arch/arm/mach-dove/mpp.c:       orion_mpp_conf(mpp_list, 0, MPP_MAX,
DOVE_MPP_VIRT_BASE);
arch/arm/mach-dove/mpp.c-
--
arch/arm/mach-mv78xx0/mpp.c:    orion_mpp_conf(mpp_list, mv78xx0_variant(),
arch/arm/mach-mv78xx0/mpp.c-                   MPP_MAX, DEV_BUS_VIRT_BASE);
--
arch/arm/mach-orion5x/mpp.c:    orion_mpp_conf(mpp_list, orion5x_variant(),
arch/arm/mach-orion5x/mpp.c-                   MPP_MAX,
ORION5X_DEV_BUS_VIRT_BASE);

arch/arm/mach-dove/mpp.h:#define MPP_MAX                        23
arch/arm/mach-mv78xx0/mpp.h:#define MPP_MAX            49
arch/arm/mach-orion5x/mpp.h:#define MPP_MAX                     19

>  {
>         unsigned int mpp_nr_regs = (1 + mpp_max/8);
> -       u32 mpp_ctrl[mpp_nr_regs];
> +       u32 mpp_ctrl[8];

Largest possible is 1 + 49 / 8 == 7. But 8 makes it nice an round. :)

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

>         int i;
>
>         printk(KERN_DEBUG "initial MPP regs:");
> +       if (mpp_nr_regs > ARRAY_SIZE(mpp_ctrl)) {
> +               printk(KERN_ERR "orion_mpp_conf: invalid mpp_max\n");
> +               return;
> +       }
> +
>         for (i = 0; i < mpp_nr_regs; i++) {
>                 mpp_ctrl[i] = readl(mpp_ctrl_addr(i, dev_bus));
>                 printk(" %08x", mpp_ctrl[i]);
> --
> 2.18.0
>

-Kees

-- 
Kees Cook
Pixel Security