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

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Date:   Wed, 13 Oct 2021 09:50:48 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     "Ivan T. Ivanov" <iivanov@...e.de>
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] Re: [PATCH] Revert "efi/random: Treat EFI_RNG_PROTOCOL
 output as bootloader randomness"

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);