linux-kernel - Re: [RESEND] [PATCH] Revert "efi/random: Treat EFI_RNG_PROTOCOL output as bootloader randomness"

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Date:   Wed, 13 Oct 2021 12:51:57 +0300
From:   "Ivan T. Ivanov" <iivanov@...e.de>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Dominik Brodowski <linux@...inikbrodowski.net>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND] [PATCH] Revert "efi/random: Treat EFI_RNG_PROTOCOL
 output as bootloader randomness"

Hi,

> On 13 Oct 2021, at 10:50, Ard Biesheuvel <ardb@...nel.org> wrote:
> 
> On Wed, 13 Oct 2021 at 09:30, Ivan T. Ivanov <iivanov@...e.de> wrote:
>> 
>> Hi,
>> 
>> Quoting Dominik Brodowski (2021-10-12 11:40:34)
>>> Am Tue, Oct 12, 2021 at 11:27:08AM +0300 schrieb Ivan T. Ivanov:
>>>> This reverts commit 18b915ac6b0ac5ba7ded03156860f60a9f16df2b.
>>>> 
>>>> When CONFIG_RANDOM_TRUST_BOOTLOADER is enabled add_bootloader_randomness()
>>>> calls add_hwgenerator_randomness() which might sleep,
>>> 
>>> Wouldn't it be better to fix add_bootloader_randomness(), considering
>>> that
>>> calls to that function are likely to happen quite early during kernel
>>> initialization? Especially as it seems to have worked beforehand?
>> 
>> I have tried. I made wait_event_interruptible() optional, but then
>> crng_reseed() segfault badly. And I don't think crng_reseed() is
>> something that I could fix easily. Suggestions are welcomed ;-)
>> 
> 
> How about
> 
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 605969ed0f96..1828dc691ebf 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -2297,9 +2297,8 @@ EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
>  */
> void add_bootloader_randomness(const void *buf, unsigned int size)
> {
> +       add_device_randomness(buf, size);
>        if (IS_ENABLED(CONFIG_RANDOM_TRUST_BOOTLOADER))
> -               add_hwgenerator_randomness(buf, size, size * 8);
> -       else
> -               add_device_randomness(buf, size);
> +               credit_entropy(&input_pool, size * 8);
> }
> EXPORT_SYMBOL_GPL(add_bootloader_randomness);

This doesn’t boot. I just changed following and kernel panics.  

- credit_entropy
+ credit_entropy_bits

Please see attached file.

Regards,
Ivan