linux-kernel - Re: [PATCH 5.5 regression fix 2/2] efi/libstub/helper: Initialize pointer variables to zero for mixed mode

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Date:   Thu, 12 Dec 2019 11:29:37 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 5.5 regression fix 2/2] efi/libstub/helper: Initialize
 pointer variables to zero for mixed mode

On Thu, 12 Dec 2019 at 11:32, Hans de Goede <hdegoede@...hat.com> wrote:
>
> When running in EFI mixed mode (running a 64 bit kernel on 32 bit EFI
> firmware), we _must_ initialize any pointers which are returned by
> reference by an EFI call to NULL before making the EFI call.
>
> In mixed mode pointers are 64 bit, but when running on a 32 bit firmware,
> EFI calls which return a pointer value by reference only fill the lower
> 32 bits of the passed pointer, leaving the upper 32 bits uninitialized
> unless we explicitly set them to 0 before the call.
>
> We have had this bug in the efi-stub-helper.c file reading code for
> a while now, but this has likely not been noticed sofar because
> this code only gets triggered when LILO style file=... arguments are
> present on the kernel cmdline.
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
>  drivers/firmware/efi/libstub/efi-stub-helper.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/efi-stub-helper.c b/drivers/firmware/efi/libstub/efi-stub-helper.c
> index e02579907f2e..6ca7d86743af 100644
> --- a/drivers/firmware/efi/libstub/efi-stub-helper.c
> +++ b/drivers/firmware/efi/libstub/efi-stub-helper.c
> @@ -365,7 +365,7 @@ static efi_status_t efi_file_size(efi_system_table_t *sys_table_arg, void *__fh,
>                                   u64 *file_sz)
>  {
>         efi_file_handle_t *h, *fh = __fh;

What about h? Doesn't it suffer from the same problem?

> -       efi_file_info_t *info;
> +       efi_file_info_t *info = NULL;
>         efi_status_t status;
>         efi_guid_t info_guid = EFI_FILE_INFO_ID;
>         unsigned long info_sz;

And info_sz?


> @@ -527,7 +527,7 @@ efi_status_t handle_cmdline_files(efi_system_table_t *sys_table_arg,
>                                   unsigned long *load_addr,
>                                   unsigned long *load_size)
>  {
> -       struct file_info *files;
> +       struct file_info *files = NULL;
>         unsigned long file_addr;
>         u64 file_size_total;
>         efi_file_handle_t *fh = NULL;
> --
> 2.23.0
>