linux-kernel - [PATCH v2] efi: random: fix NULL-deref when refreshing seed

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Message-Id: <20221219101237.9872-1-johan+linaro@kernel.org>
Date:   Mon, 19 Dec 2022 11:12:37 +0100
From:   Johan Hovold <johan+linaro@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Johan Hovold <johan+linaro@...nel.org>,
        Steev Klimaszewski <steev@...i.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Andrew Halaney <ahalaney@...hat.com>
Subject: [PATCH v2] efi: random: fix NULL-deref when refreshing seed

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, or more generally, whenever
the runtime services have been disabled (e.g. efi=noruntime or with
PREEMPT_RT).

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>
Tested-by: Andrew Halaney <ahalaney@...hat.com> # sc8280xp-lenovo-thinkpad-x13s
Signed-off-by: Johan Hovold <johan+linaro@...nel.org>
---

Changes in v2
 - amend commit message with a comment on this being needed whenever the
   runtime services have been disabled


 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 31a4090c66b3..09716eebe8ac 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -429,7 +429,9 @@ 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