On Tue, Sep 06, 2022 at 12:36:56PM +0200, Jason A. Donenfeld wrote:
> It's only safe to modify the setup_data pointer on newer kernels where
> the EFI stub loader will ignore it. So condition setting that offset on
> the newer boot protocol version. While we're at it, gate this on SEV too.
> This depends on the kernel commit linked below going upstream.
>
> Cc: Gerd Hoffmann <[email protected]>
> Cc: Laurent Vivier <[email protected]>
> Cc: Michael S. Tsirkin <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Peter Maydell <[email protected]>
> Cc: Philippe Mathieu-Daudé <[email protected]>
> Cc: Richard Henderson <[email protected]>
> Cc: Ard Biesheuvel <[email protected]>
> Link:
> https://lore.kernel.org/linux-efi/[email protected]/
> Signed-off-by: Jason A. Donenfeld <[email protected]>
BTW what does it have to do with SEV?
Is this because SEV is not going to trust the data to be random anyway?
> ---
> hw/i386/x86.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/hw/i386/x86.c b/hw/i386/x86.c
> index 050eedc0c8..fddc20df03 100644
> --- a/hw/i386/x86.c
> +++ b/hw/i386/x86.c
> @@ -1088,8 +1088,15 @@ void x86_load_linux(X86MachineState *x86ms,
> qemu_guest_getrandom_nofail(setup_data->data, RNG_SEED_LENGTH);
> }
>
> - /* Offset 0x250 is a pointer to the first setup_data link. */
> - stq_p(header + 0x250, first_setup_data);
> + /*
> + * Only modify the header if doing so won't crash EFI boot, which is the
> + * case only for newer boot protocols, and don't do so either if SEV is
> + * enabled.
> + */
> + if (protocol >= 0x210 && !sev_enabled()) {
> + /* Offset 0x250 is a pointer to the first setup_data link. */
> + stq_p(header + 0x250, first_setup_data);
> + }
>
> /*
> * If we're starting an encrypted VM, it will be OVMF based, which uses
> the
> --
> 2.37.3
