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

From: Hans de Goede
Date: Thu Dec 12 2019 - 07:45:15 EST


On 12-12-2019 12:29, Ard Biesheuvel wrote:
On Thu, 12 Dec 2019 at 11:32, Hans de Goede <hdegoede@xxxxxxxxxx> 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@xxxxxxxxxxxxxxx
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
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?

And "efi_file_io_interface_t *io" and "efi_file_handle_t *fh"
in efi_open_volume().

I think that is all of them.