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From: Heinrich Schuchardt <xypron.glpk@gmx.de>
To: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: ardb@kernel.org, mark.kettenis@xs4all.nl,
	Alexander Graf <agraf@csgraf.de>,
	u-boot@lists.denx.de
Subject: Re: [PATCH v2] efi_loader: Get rid of kaslr-seed
Date: Fri, 17 Dec 2021 11:59:42 +0100	[thread overview]
Message-ID: <a2cc0b09-3bdd-f721-eb67-cd81076aded7@gmx.de> (raw)
In-Reply-To: <20211217070644.2458603-1-ilias.apalodimas@linaro.org>

On 12/17/21 08:06, Ilias Apalodimas wrote:
> Right now we unconditionally pass a 'kaslr-seed' property to the kernel
> if the DTB we ended up in EFI includes the entry.  However the kernel
> EFI stub completely ignores it and only relies on EFI_RNG_PROTOCOL for
> it's own randomness needs (i.e the randomization of the physical
> placement of the kernel).
> So let's get rid of it if EFI_RNG_PPROTOCOL is installed.
>
> It's worth noting that TPMs also provide an RNG.  So if we tweak our
> EFI_RNG_PROTOCOL slightly and install the protocol when a TPM device
> is present the 'kaslr-seed' property will always be removed, allowing
> us to reliably measure our DTB as well.
>
> Acked-by: Ard Biesheuvel <ardb@kernel.org>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
> ---
> changes since v1:
> - Only removing the property if EFI_RNG_PROTOCOL is installed, since some
>    OS'es rely on kaslr-seed

Each TPMv2 provides a hardware RNG. So you can unconditionally remove
the kaslr-seed and create a new one by calling TPM2_GetRandom().

It would further be useful to provide a DM RNG driver using
TPM2_GetRandom().

Best regards

Heinrich

  reply	other threads:[~2021-12-17 10:59 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-17  7:06 [PATCH v2] efi_loader: Get rid of kaslr-seed Ilias Apalodimas
2021-12-17 10:59 ` Heinrich Schuchardt [this message]
2021-12-17 11:13   ` Ilias Apalodimas
2021-12-17 11:13 ` Mark Kettenis
2021-12-17 11:23   ` Ilias Apalodimas
2021-12-17 11:33     ` Mark Kettenis
2022-01-02 10:05       ` Heinrich Schuchardt
2022-01-02 20:50         ` Ilias Apalodimas
2022-01-02 21:06           ` Heinrich Schuchardt
2022-01-02 21:27             ` Mark Kettenis
2022-01-03  7:30               ` Ilias Apalodimas
2022-01-03  7:27             ` Ilias Apalodimas

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