Re: [PATCH v8 18/22] tpm: add session encryption protection to tpm2_get_random()

James Bottomley
2024-05-17T14:25:43Z

On Fri, 2024-05-17 at 15:43 +0200, Ard Biesheuvel wrote:
> On Fri, 17 May 2024 at 15:35, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
[...]
> > Thanks for the analysis.  If I look at how CRYPTO_ECC does it, that
> > selects CRYPTO_RNG_DEFAULT which pulls in CRYPTO_DRBG, so the fix
> > would be the attached.  Does that look right to you Ard?
>
> No it doesn't - it's CRYPTO_RNG_DEFAULT not CRYTPO_RNG_DEFAULT :-)
>
> With that fixed,
>
> Acked-by: Ard Biesheuvel <ardb@kernel.org>

Erm, oops, sorry about that; so attached is the update.

James

---8>8>8><8<8<8---

From 2ac337a33e6416ef806e2c692b9239d193e8468f Mon Sep 17 00:00:00 2001
From: James Bottomley <James.Bottomley@HansenPartnership.com>
Date: Fri, 17 May 2024 06:29:31 -0700
Subject: [PATCH] tpm: Fix sessions cryptography requirement for Random Numbers
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The ECDH code in tpm2-sessions.c requires an initial random number
generator to generate the key pair. If the configuration doesn't have
CONFIG_RNG_DEFAULT, it will try to pull this in as a module (which is
impossible for the early kernel boot where the TPM starts). Fix this
by selecting the required RNG.

Reported-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Fixes: 1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()")
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
---
drivers/char/tpm/Kconfig | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
index 4f83ee7021d0..ecdd3db4be2b 100644
--- a/drivers/char/tpm/Kconfig
+++ b/drivers/char/tpm/Kconfig
@@ -31,6 +31,7 @@ config TCG_TPM2_HMAC
bool "Use HMAC and encrypted transactions on the TPM bus"
default y
select CRYPTO_ECDH
+ select CRYPTO_RNG_DEFAULT
select CRYPTO_LIB_AESCFB
select CRYPTO_LIB_SHA256
help
--
2.35.3