[v2] efi: random: fix NULL-deref when refreshing seed

Do not try to refresh the RNG seed in case the firmware does not support
setting variables.

This is specifically needed to prevent a NULL-pointer dereference on the
Lenovo X13s with some firmware revisions, or more generally, whenever
the runtime services have been disabled (e.g. efi=noruntime or with
PREEMPT_RT).

Fixes: e7b813b32a42 ("efi: random: refresh non-volatile random seed when RNG is initialized")
Reported-by: Steev Klimaszewski <steev@kali.org>
Reported-by: Bjorn Andersson <andersson@kernel.org>
Tested-by: Andrew Halaney <ahalaney@redhat.com> # sc8280xp-lenovo-thinkpad-x13s
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---

Changes in v2
 - amend commit message with a comment on this being needed whenever the
   runtime services have been disabled


 drivers/firmware/efi/efi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

On Mon, Dec 19, 2022 at 03:00:17PM +0100, Jason A. Donenfeld wrote:
> On Mon, Dec 19, 2022 at 11:12:37AM +0100, Johan Hovold wrote:
> > Do not try to refresh the RNG seed in case the firmware does not support
> > setting variables.
> > 
> > This is specifically needed to prevent a NULL-pointer dereference on the
> > Lenovo X13s with some firmware revisions, or more generally, whenever
> > the runtime services have been disabled (e.g. efi=noruntime or with
> > PREEMPT_RT).
> > 
> > Fixes: e7b813b32a42 ("efi: random: refresh non-volatile random seed when RNG is initialized")
> > Reported-by: Steev Klimaszewski <steev@kali.org>
> > Reported-by: Bjorn Andersson <andersson@kernel.org>
> > Tested-by: Andrew Halaney <ahalaney@redhat.com> # sc8280xp-lenovo-thinkpad-x13s
> > Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> > ---
> > 
> > Changes in v2
> >  - amend commit message with a comment on this being needed whenever the
> >    runtime services have been disabled
> 
> I'll queue up the one with the amended commit message.

Perfect, thanks!

Johan

On Mon, Dec 19, 2022 at 4:13 AM Johan Hovold <johan+linaro@kernel.org> wrote:
>
> Do not try to refresh the RNG seed in case the firmware does not support
> setting variables.
>
> This is specifically needed to prevent a NULL-pointer dereference on the
> Lenovo X13s with some firmware revisions, or more generally, whenever
> the runtime services have been disabled (e.g. efi=noruntime or with
> PREEMPT_RT).
>
> Fixes: e7b813b32a42 ("efi: random: refresh non-volatile random seed when RNG is initialized")
> Reported-by: Steev Klimaszewski <steev@kali.org>
> Reported-by: Bjorn Andersson <andersson@kernel.org>
> Tested-by: Andrew Halaney <ahalaney@redhat.com> # sc8280xp-lenovo-thinkpad-x13s
> Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
> ---
>
> Changes in v2
>  - amend commit message with a comment on this being needed whenever the
>    runtime services have been disabled
>
>
>  drivers/firmware/efi/efi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 31a4090c66b3..09716eebe8ac 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -429,7 +429,9 @@ static int __init efisubsys_init(void)
>                 platform_device_register_simple("efi_secret", 0, NULL, 0);
>  #endif
>
> -       execute_with_initialized_rng(&refresh_nv_rng_seed_nb);
> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_SET_VARIABLE))
> +               execute_with_initialized_rng(&refresh_nv_rng_seed_nb);
> +
>         return 0;
>
>  err_remove_group:
> --
> 2.37.4
>
Andrew already sent one, but also confirming since I reported it, this
fixes the issue for me as well.
Tested-by: Steev Klimaszewski <steev@kali.org>