linux-kernel - Re: [PATCH] powerpc/msi: Remove VLA usage

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Message-ID: <CAGXu5jKV-YAQZtN2heFdmiD9EOZ-AqrBc-NjC8fRYLSafovuyQ@mail.gmail.com>
Date:   Mon, 16 Jul 2018 20:56:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>,
        Rob Herring <robh@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        PowerPC <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/msi: Remove VLA usage

On Fri, Jun 29, 2018 at 11:52 AM, Kees Cook <keescook@...omium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> switches from an unchanging variable to a constant expression to eliminate
> the VLA generation.
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Friendly ping! Michael, can you take this?

-Kees


> ---
>  arch/powerpc/sysdev/msi_bitmap.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/sysdev/msi_bitmap.c b/arch/powerpc/sysdev/msi_bitmap.c
> index 6243a7e537d0..e64a411d1a00 100644
> --- a/arch/powerpc/sysdev/msi_bitmap.c
> +++ b/arch/powerpc/sysdev/msi_bitmap.c
> @@ -225,22 +225,23 @@ static void __init test_of_node(void)
>         struct device_node of_node;
>         struct property prop;
>         struct msi_bitmap bmp;
> -       int size = 256;
> -       DECLARE_BITMAP(expected, size);
> +#define SIZE_EXPECTED 256
> +       DECLARE_BITMAP(expected, SIZE_EXPECTED);
>
>         /* There should really be a struct device_node allocator */
>         memset(&of_node, 0, sizeof(of_node));
>         of_node_init(&of_node);
>         of_node.full_name = node_name;
>
> -       WARN_ON(msi_bitmap_alloc(&bmp, size, &of_node));
> +       WARN_ON(msi_bitmap_alloc(&bmp, SIZE_EXPECTED, &of_node));
>
>         /* No msi-available-ranges, so expect > 0 */
>         WARN_ON(msi_bitmap_reserve_dt_hwirqs(&bmp) <= 0);
>
>         /* Should all still be free */
> -       WARN_ON(bitmap_find_free_region(bmp.bitmap, size, get_count_order(size)));
> -       bitmap_release_region(bmp.bitmap, 0, get_count_order(size));
> +       WARN_ON(bitmap_find_free_region(bmp.bitmap, SIZE_EXPECTED,
> +                                       get_count_order(SIZE_EXPECTED)));
> +       bitmap_release_region(bmp.bitmap, 0, get_count_order(SIZE_EXPECTED));
>
>         /* Now create a fake msi-available-ranges property */
>
> @@ -256,8 +257,8 @@ static void __init test_of_node(void)
>         WARN_ON(msi_bitmap_reserve_dt_hwirqs(&bmp));
>
>         /* Check we got the expected result */
> -       WARN_ON(bitmap_parselist(expected_str, expected, size));
> -       WARN_ON(!bitmap_equal(expected, bmp.bitmap, size));
> +       WARN_ON(bitmap_parselist(expected_str, expected, SIZE_EXPECTED));
> +       WARN_ON(!bitmap_equal(expected, bmp.bitmap, SIZE_EXPECTED));
>
>         msi_bitmap_free(&bmp);
>         kfree(bmp.bitmap);
> --
> 2.17.1
>
>
> --
> Kees Cook
> Pixel Security



-- 
Kees Cook
Pixel Security