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

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Date:   Tue, 12 Oct 2021 11:27:08 +0300
From:   "Ivan T. Ivanov" <iivanov@...e.de>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Dominik Brodowski <linux@...inikbrodowski.net>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Ivan T. Ivanov" <iivanov@...e.de>
Subject: [PATCH] Revert "efi/random: Treat EFI_RNG_PROTOCOL output as bootloader randomness"

This reverts commit 18b915ac6b0ac5ba7ded03156860f60a9f16df2b.

When CONFIG_RANDOM_TRUST_BOOTLOADER is enabled add_bootloader_randomness()
calls add_hwgenerator_randomness() which might sleep, but this is not
possible during early kernel initialization. This revert fixes following
NULL pointer deference:

[    0.000000] efi: seeding entropy pool
[    0.000000] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
...
[    0.000000] pc : kthread_should_stop+0x2c/0x60
[    0.000000] lr : add_hwgenerator_randomness+0x58/0x178
...
[    0.000000] Call trace:
[    0.000000]  kthread_should_stop+0x2c/0x60
[    0.000000]  add_bootloader_randomness+0x2c/0x38
[    0.000000]  efi_config_parse_tables+0x120/0x250
[    0.000000]  efi_init+0x138/0x1e0
[    0.000000]  setup_arch+0x394/0x778
[    0.000000]  start_kernel+0x90/0x568

Signed-off-by: Ivan T. Ivanov <iivanov@...e.de>
---
 drivers/firmware/efi/efi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 847f33ffc4ae..8aad3c524947 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -600,7 +600,7 @@ int __init efi_config_parse_tables(const efi_config_table_t *config_tables,
 					      sizeof(*seed) + size);
 			if (seed != NULL) {
 				pr_notice("seeding entropy pool\n");
-				add_bootloader_randomness(seed->bits, size);
+				add_device_randomness(seed->bits, size);
 				early_memunmap(seed, sizeof(*seed) + size);
 			} else {
 				pr_err("Could not map UEFI random seed!\n");
-- 
2.33.0