linux-kernel - Re: [PATCH] efi: random: fix NULL-deref when refreshing seed

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Date:   Fri, 16 Dec 2022 10:28:30 -0600
From:   Andrew Halaney <ahalaney@...hat.com>
To:     Johan Hovold <johan+linaro@...nel.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, Steev Klimaszewski <steev@...i.org>,
        Bjorn Andersson <andersson@...nel.org>
Subject: Re: [PATCH] efi: random: fix NULL-deref when refreshing seed

On Fri, Dec 16, 2022 at 10:15:14AM +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.
> 
> Fixes: e7b813b32a42 ("efi: random: refresh non-volatile random seed when RNG is initialized")
> Reported-by: Steev Klimaszewski <steev@...i.org>
> Reported-by: Bjorn Andersson <andersson@...nel.org>
> Signed-off-by: Johan Hovold <johan+linaro@...nel.org>

Tested-by: Andrew Halaney <ahalaney@...hat.com> # sc8280xp-lenovo-thinkpad-x13s

Thanks Johan, this fixes the boot issue I was blindly fighting
yesterday.

> ---
>  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 2e168e5b97de..1a9e2f70c550 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -432,7 +432,9 @@ 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
>