linux-kernel - Re: [PATCH v6 10/18] x86/power/64: Remove VLA usage

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Message-ID: <CAJZ5v0gVDotjufLKUW0YuQu2vA4fmU_gqia=ZA4DocW4XHxx0w@mail.gmail.com>
Date:   Wed, 25 Jul 2018 13:32:23 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Biggers <ebiggers@...gle.com>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Alasdair Kergon <agk@...hat.com>,
        Rabin Vincent <rabinv@...s.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Philipp Reisner <philipp.reisner@...bit.com>,
        Lars Ellenberg <lars.ellenberg@...bit.com>,
        Jens Axboe <axboe@...nel.dk>,
        Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Howells <dhowells@...hat.com>,
        Johannes Berg <johannes@...solutions.net>,
        Tudor-Dan Ambarus <tudor.ambarus@...rochip.com>,
        Jia-Ju Bai <baijiaju1990@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Will Deacon <will.deacon@....com>, dm-devel@...hat.com,
        Linux PM <linux-pm@...r.kernel.org>,
        linux-crypto@...r.kernel.org, drbd-dev@...ts.linbit.com,
        linux-block@...r.kernel.org, qat-linux@...el.com,
        linux-ppp@...r.kernel.org, netdev <netdev@...r.kernel.org>,
        devel@...verdev.osuosl.org, linux-afs@...ts.infradead.org,
        "open list:NETWORKING DRIVERS (WIRELESS)" 
        <linux-wireless@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 10/18] x86/power/64: Remove VLA usage

On Tue, Jul 24, 2018 at 6:49 PM, Kees Cook <keescook@...omium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> removes the discouraged use of AHASH_REQUEST_ON_STACK by switching to
> shash directly and allocating the descriptor in heap memory (which should
> be fine: the tfm has already been allocated there too).
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> Acked-by: Pavel Machek <pavel@....cz>

I think I can queue this up if there are no objections from others.

Do you want me to do that?

> ---
>  arch/x86/power/hibernate_64.c | 36 ++++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/power/hibernate_64.c b/arch/x86/power/hibernate_64.c
> index 67ccf64c8bd8..f8e3b668d20b 100644
> --- a/arch/x86/power/hibernate_64.c
> +++ b/arch/x86/power/hibernate_64.c
> @@ -233,29 +233,35 @@ struct restore_data_record {
>   */
>  static int get_e820_md5(struct e820_table *table, void *buf)
>  {
> -       struct scatterlist sg;
> -       struct crypto_ahash *tfm;
> +       struct crypto_shash *tfm;
> +       struct shash_desc *desc;
>         int size;
>         int ret = 0;
>
> -       tfm = crypto_alloc_ahash("md5", 0, CRYPTO_ALG_ASYNC);
> +       tfm = crypto_alloc_shash("md5", 0, 0);
>         if (IS_ERR(tfm))
>                 return -ENOMEM;
>
> -       {
> -               AHASH_REQUEST_ON_STACK(req, tfm);
> -               size = offsetof(struct e820_table, entries) + sizeof(struct e820_entry) * table->nr_entries;
> -               ahash_request_set_tfm(req, tfm);
> -               sg_init_one(&sg, (u8 *)table, size);
> -               ahash_request_set_callback(req, 0, NULL, NULL);
> -               ahash_request_set_crypt(req, &sg, buf, size);
> -
> -               if (crypto_ahash_digest(req))
> -                       ret = -EINVAL;
> -               ahash_request_zero(req);
> +       desc = kmalloc(sizeof(struct shash_desc) + crypto_shash_descsize(tfm),
> +                      GFP_KERNEL);
> +       if (!desc) {
> +               ret = -ENOMEM;
> +               goto free_tfm;
>         }
> -       crypto_free_ahash(tfm);
>
> +       desc->tfm = tfm;
> +       desc->flags = 0;
> +
> +       size = offsetof(struct e820_table, entries) +
> +               sizeof(struct e820_entry) * table->nr_entries;
> +
> +       if (crypto_shash_digest(desc, (u8 *)table, size, buf))
> +               ret = -EINVAL;
> +
> +       kzfree(desc);
> +
> +free_tfm:
> +       crypto_free_shash(tfm);
>         return ret;
>  }
>
> --
> 2.17.1
>