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

Rafael J. Wysocki
2018-07-25T11:32:23Z

On Tue, Jul 24, 2018 at 6:49 PM, Kees Cook <keescook@chromium.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@chromium.org>
> Acked-by: Pavel Machek <pavel@ucw.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
>