(cc Kees)
On Thu, 18 Aug 2022 at 08:58, Daniel Marth
<daniel.marth@xxxxxxxxxxxxxxxxx> wrote:
>
> Randstruct by default randomizes structures that consist entirely of
> function pointers, even if they are not explicitly labeled for
> randomization. efi_rng_protocol contains an anonymous structure that is
> affected by this implicit selection process. Randomization of this
> structure causes a data layout inconsistency between the kernel and the
> EFI. In this scenario the Arm64 boot process fails with the following
> output:
> EFI stub: Booting Linux Kernel...
> EFI stub: ERROR: efi_get_random_bytes() failed (0x8000000000000002)
> EFI stub: Using DTB from configuration table
> EFI stub: Loaded initrd from LINUX_EFI_INITRD_MEDIA_GUID device path
> Synchronous Exception at 0x0000000081310C90
> Synchronous Exception at 0x0000000081310C90
>
> efi_get_random_bytes() fails in handle_kernel_image (arm64-stub.c)
> because it uses an incorrect structure layout for efi_call_proto. Add
> the __no_randomize_layout annotation to the anonymous structure within
> efi_rng_protocol to prevent its randomization and resolve this issue.
>
> This patch was tested for the Arm64 architecture using QEMU. In
> addition to the current next branch of this subsystem, also minor
> versions 4.16 to 5.1, 5.5 and 5.6 were tested successfully with a
> (backported) version of this patch.
>
> Signed-off-by: Daniel Marth <daniel.marth@xxxxxxxxxxxxxxxxx>
Thanks for the patch.
> ---
> drivers/firmware/efi/libstub/random.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c
> index 24aa37535372..54fa980cf1af 100644
> --- a/drivers/firmware/efi/libstub/random.c
> +++ b/drivers/firmware/efi/libstub/random.c
> @@ -18,7 +18,7 @@ union efi_rng_protocol {
> efi_status_t (__efiapi *get_rng)(efi_rng_protocol_t *,
> efi_guid_t *, unsigned long,
> u8 *out);
> - };
> + } __no_randomize_layout;
> struct {
> u32 get_info;
> u32 get_rng;
This may work around the problem, but I'd like to fix this more
thoroughly if we can. EFI protocols are not randomizable by nature, as
they are a contract between the firmware and the OS, so struct
randomization should just be disabled for the entire EFI stub, i.e.,
everything below libstub/
Kees?
