Re: [PATCH v2 3/4] tee: Remove call to get_kernel_pages()

[Sumit Garg]

On Sat, 4 Feb 2023 at 09:36, Ira Weiny <ira.weiny@xxxxxxxxx> wrote:
>
> The kernel pages used by shm_get_kernel_pages() are allocated using
> GFP_KERNEL through the following call stack:
>
> trusted_instantiate()
>         trusted_payload_alloc() -> GFP_KERNEL
>         <trusted key op>
>                 tee_shm_register_kernel_buf()
>                         register_shm_helper()
>                                 shm_get_kernel_pages()
>
> Where <trusted key op> is one of:
>
>         trusted_key_unseal()
>         trusted_key_get_random()
>         trusted_key_seal()
>
> Because the pages can't be from highmem get_kernel_pages() boils down to
> a get_page() call.
>
> Remove the get_kernel_pages() call and open code the get_page().
>
> In case a highmem page does slip through warn on once for a kmap'ed
> address.
>
> Cc: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> ---
> Changes from v1:
>         Al/Christoph: Remove kiov altogether
> ---
>  drivers/tee/tee_shm.c | 21 ++++++++-------------
>  1 file changed, 8 insertions(+), 13 deletions(-)
>

Reviewed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>

-Sumit

> diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> index 527a6eabc03e..b1c6231defad 100644
> --- a/drivers/tee/tee_shm.c
> +++ b/drivers/tee/tee_shm.c
> @@ -11,6 +11,7 @@
>  #include <linux/tee_drv.h>
>  #include <linux/uaccess.h>
>  #include <linux/uio.h>
> +#include <linux/highmem.h>
>  #include "tee_private.h"
>
>  static void shm_put_kernel_pages(struct page **pages, size_t page_count)
> @@ -24,26 +25,20 @@ static void shm_put_kernel_pages(struct page **pages, size_t page_count)
>  static int shm_get_kernel_pages(unsigned long start, size_t page_count,
>                                 struct page **pages)
>  {
> -       struct kvec *kiov;
> +       struct page *page;
>         size_t n;
> -       int rc;
>
> -       if (WARN_ON_ONCE(is_vmalloc_addr((void *)start)))
> +       if (WARN_ON_ONCE(is_vmalloc_addr((void *)start) ||
> +                        is_kmap_addr((void *)start)))
>                 return -EINVAL;
>
> -       kiov = kcalloc(page_count, sizeof(*kiov), GFP_KERNEL);
> -       if (!kiov)
> -               return -ENOMEM;
> -
> +       page = virt_to_page(start);
>         for (n = 0; n < page_count; n++) {
> -               kiov[n].iov_base = (void *)(start + n * PAGE_SIZE);
> -               kiov[n].iov_len = PAGE_SIZE;
> +               pages[n] = page + n;
> +               get_page(pages[n]);
>         }
>
> -       rc = get_kernel_pages(kiov, page_count, 0, pages);
> -       kfree(kiov);
> -
> -       return rc;
> +       return page_count;
>  }
>
>  static void release_registered_pages(struct tee_shm *shm)
>
> --
> 2.39.1