Re: [PATCH 6/9] pm: hibernate: Optionally store and verify a hash of the image

[Evan Green]

On Fri, Feb 19, 2021 at 5:36 PM Matthew Garrett
<matthewgarrett@xxxxxxxxxx> wrote:
>
> Calculate and store a cryptographically secure hash of the hibernation
> image if SF_VERIFY_IMAGE is set in the hibernation flags. This allows
> detection of a corrupt image, but has the disadvantage that it requires
> the blocks be read in in linear order.
>
> Signed-off-by: Matthew Garrett <mjg59@xxxxxxxxxx>
> ---
>  kernel/power/power.h |   1 +
>  kernel/power/swap.c  | 131 +++++++++++++++++++++++++++++++++++--------
>  2 files changed, 110 insertions(+), 22 deletions(-)
>
> diff --git a/kernel/power/power.h b/kernel/power/power.h
> index 778bf431ec02..b8e00b9dcee8 100644
> --- a/kernel/power/power.h
> +++ b/kernel/power/power.h
> @@ -168,6 +168,7 @@ extern int swsusp_swap_in_use(void);
>  #define SF_PLATFORM_MODE       1
>  #define SF_NOCOMPRESS_MODE     2
>  #define SF_CRC32_MODE          4
> +#define SF_VERIFY_IMAGE         8
>
>  /* kernel/power/hibernate.c */
>  extern int swsusp_check(void);
> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
> index 72e33054a2e1..a13241a20567 100644
> --- a/kernel/power/swap.c
> +++ b/kernel/power/swap.c
> @@ -31,6 +31,8 @@
>  #include <linux/kthread.h>
>  #include <linux/crc32.h>
>  #include <linux/ktime.h>
> +#include <crypto/hash.h>
> +#include <crypto/sha2.h>
>
>  #include "power.h"
>
> @@ -95,17 +97,20 @@ struct swap_map_page_list {
>  struct swap_map_handle {
>         struct swap_map_page *cur;
>         struct swap_map_page_list *maps;
> +       struct shash_desc *desc;
>         sector_t cur_swap;
>         sector_t first_sector;
>         unsigned int k;
>         unsigned long reqd_free_pages;
>         u32 crc32;
> +       u8 digest[SHA256_DIGEST_SIZE];
>  };
>
>  struct swsusp_header {
>         char reserved[PAGE_SIZE - 20 - sizeof(sector_t) - sizeof(int) -
> -                     sizeof(u32)];
> +                     sizeof(u32) - SHA256_DIGEST_SIZE];
>         u32     crc32;
> +       u8      digest[SHA256_DIGEST_SIZE];
>         sector_t image;
>         unsigned int flags;     /* Flags to pass to the "boot" kernel */
>         char    orig_sig[10];
> @@ -305,6 +310,9 @@ static blk_status_t hib_wait_io(struct hib_bio_batch *hb)
>          * We are relying on the behavior of blk_plug that a thread with
>          * a plug will flush the plug list before sleeping.
>          */
> +       if (!hb)
> +               return 0;
> +
>         wait_event(hb->wait, atomic_read(&hb->count) == 0);
>         return blk_status_to_errno(hb->error);
>  }
> @@ -327,6 +335,8 @@ static int mark_swapfiles(struct swap_map_handle *handle, unsigned int flags)
>                 swsusp_header->flags = flags;
>                 if (flags & SF_CRC32_MODE)
>                         swsusp_header->crc32 = handle->crc32;
> +               memcpy(swsusp_header->digest, handle->digest,
> +                      SHA256_DIGEST_SIZE);
>                 error = hib_submit_io(REQ_OP_WRITE, REQ_SYNC,
>                                       swsusp_resume_block, swsusp_header, NULL);
>         } else {
> @@ -417,6 +427,7 @@ static void release_swap_writer(struct swap_map_handle *handle)
>  static int get_swap_writer(struct swap_map_handle *handle)
>  {
>         int ret;
> +       struct crypto_shash *tfm;
>
>         ret = swsusp_swap_check();
>         if (ret) {
> @@ -437,7 +448,28 @@ static int get_swap_writer(struct swap_map_handle *handle)
>         handle->k = 0;
>         handle->reqd_free_pages = reqd_free_pages();
>         handle->first_sector = handle->cur_swap;
> +
> +       tfm = crypto_alloc_shash("sha256", 0, 0);
> +       if (IS_ERR(tfm)) {
> +               ret = -EINVAL;
> +               goto err_rel;
> +       }
> +       handle->desc = kmalloc(sizeof(struct shash_desc) +
> +                              crypto_shash_descsize(tfm), GFP_KERNEL);
> +       if (!handle->desc) {
> +               ret = -ENOMEM;
> +               goto err_rel;
> +       }
> +
> +       handle->desc->tfm = tfm;
> +
> +       ret = crypto_shash_init(handle->desc);
> +       if (ret != 0)
> +               goto err_free;
> +
>         return 0;
> +err_free:
> +       kfree(handle->desc);
>  err_rel:
>         release_swap_writer(handle);
>  err_close:
> @@ -446,7 +478,7 @@ static int get_swap_writer(struct swap_map_handle *handle)
>  }
>
>  static int swap_write_page(struct swap_map_handle *handle, void *buf,
> -               struct hib_bio_batch *hb)
> +                          struct hib_bio_batch *hb, bool hash)
>  {
>         int error = 0;
>         sector_t offset;
> @@ -454,6 +486,7 @@ static int swap_write_page(struct swap_map_handle *handle, void *buf,
>         if (!handle->cur)
>                 return -EINVAL;
>         offset = alloc_swapdev_block(root_swap);
> +       crypto_shash_update(handle->desc, buf, PAGE_SIZE);

Was this supposed to be conditionalized behind the new parameter, ie:
if (hash) crypto_shash_update()? If so, the same comment would apply
to the read as well.