From patchwork Thu Oct 20 08:39:10 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 616956 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CEC5CC433FE for ; Thu, 20 Oct 2022 08:40:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229956AbiJTIkp (ORCPT ); Thu, 20 Oct 2022 04:40:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230285AbiJTIkm (ORCPT ); Thu, 20 Oct 2022 04:40:42 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1E67FFBCFC for ; Thu, 20 Oct 2022 01:40:32 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 317D561A7B for ; Thu, 20 Oct 2022 08:40:32 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 653B8C433B5; Thu, 20 Oct 2022 08:40:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666255231; bh=DidgXi01vs3QJl79fyJMKey6h/6Z2yoooMXAGEGQbow=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=m7LzqgqVvMu7nn9U+HYnAtm98jxrS4jEaqCs4h1wMIwew/WjzhAzGATI81nHR1rt9 n4zElTkByRzWgcoawhMwLEPp+4KFpzbRPAceg+/WMWctdu0bPcDfpk4yRfJvhcyYCH gp2OPD9Go0pvWTRbW24IDGlerOkR32xeGkYZQGN63oj+Ha+pOSSAgE78zG7Pn5Vep/ 5muDCkuM6I8jDw09hnk5I3xVeCo8sYUy2uKZwYGMcwEedUWMitxdCIMlkHfXCuBs2Y oxgK7vfMKquPVRmSH1FmRZTuqJVDiQwAZ8hq/+jX5G0dnBJ0OR3X/ahHQEXJrInmia IEt3zVFFNahcQ== From: Ard Biesheuvel To: linux-efi@vger.kernel.org Cc: Ard Biesheuvel , Ilias Apalodimas , "Jason A . Donenfeld" , Lennart Poettering Subject: [PATCH v3 3/3] efi: random: combine bootloader provided RNG seed with RNG protocol output Date: Thu, 20 Oct 2022 10:39:10 +0200 Message-Id: <20221020083910.1902009-4-ardb@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20221020083910.1902009-1-ardb@kernel.org> References: <20221020083910.1902009-1-ardb@kernel.org> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4851; i=ardb@kernel.org; h=from:subject; bh=DidgXi01vs3QJl79fyJMKey6h/6Z2yoooMXAGEGQbow=; b=owEB7QES/pANAwAKAcNPIjmS2Y8kAcsmYgBjUQktk5UXFUYdATXiXa5lDEJuzxwgsQagUOLcYPvL 4zN6F3OJAbMEAAEKAB0WIQT72WJ8QGnJQhU3VynDTyI5ktmPJAUCY1EJLQAKCRDDTyI5ktmPJH4JDA C7pruCaWEkzlKz1sBf0/C3n3u/EdIxPemexn/uXwibNGWozqWqrPX3At4F27NaTy+hXnQaLgG47TYW TxBd4FVvARI+5jl0lmJeJgv64pn1NmDbgiDy8k1DPoCX0z34Cc7JrwdIymfylHsCv4laJEAvI1ONsA Od89CIuTGb52GpR+DIWLRzKmQ2lWRRt5BFMNVH3lrtZr6HipMZD3fG6JaV+tJN4+5tyT69sRoDP1Pv HAbKB/PoEsbTK3NVeH5lO3J2Bsu04+vzaK6XaEBs80XFvGOOqI3Ab5EgyOKGIvo1Nscg4vMlSXWsDn 9QxfKo3AyfdzsWYwda0XnYavJ9dWHzMX5KDp0iyYLyTdm0V4APQ8+VB34O9Y9EmnHIBdaLRCZtpmyJ 9Yx6rt1lekD3vqr+4Ol0WJuuJaK4rgZQcx50xBOV8AgjSJxglImquIFouJOAEPwt9ggl5buMcnP89y IGCRX6frHfNHryuaqyA1FLSjlI73HCAPiClVrvwoleGS4= X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 Precedence: bulk List-ID: X-Mailing-List: linux-efi@vger.kernel.org Instead of blindly creating the EFI random seed configuration table if the RNG protocol is implemented and works, check whether such a EFI configuration table was provided by an earlier boot stage and if so, concatenate the existing and the new seeds, leaving it up to the core code to mix it in and credit it the way it sees fit. This can be used for, e.g., systemd-boot, to pass an additional seed to Linux in a way that can be consumed by the kernel very early. In that case, the following definitions should be used to pass the seed to the EFI stub: struct linux_efi_random_seed { u32 size; // of the 'seed' array in bytes u8 seed[]; }; The memory for the struct must be allocated as EFI_ACPI_RECLAIM_MEMORY pool memory, and the address of the struct in memory should be installed as a EFI configuration table using the following GUID: LINUX_EFI_RANDOM_SEED_TABLE_GUID 1ce1e5bc-7ceb-42f2-81e5-8aadf180f57b Note that doing so is safe even on kernels that were built without this patch applied, but the seed will simply be overwritten with a seed derived from the EFI RNG protocol, if available. The recommended seed size is 32 bytes, anything beyond that is disregarded when the seeds are concatenated. Signed-off-by: Ard Biesheuvel --- drivers/firmware/efi/libstub/efistub.h | 2 ++ drivers/firmware/efi/libstub/random.c | 29 ++++++++++++++++++-- include/linux/efi.h | 2 -- 3 files changed, 28 insertions(+), 5 deletions(-) diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h index a30fb5d8ef05..75280b800eee 100644 --- a/drivers/firmware/efi/libstub/efistub.h +++ b/drivers/firmware/efi/libstub/efistub.h @@ -882,6 +882,8 @@ efi_status_t efi_get_random_bytes(unsigned long size, u8 *out); efi_status_t efi_random_alloc(unsigned long size, unsigned long align, unsigned long *addr, unsigned long random_seed); +efi_status_t efi_random_get_seed(void); + efi_status_t check_platform_features(void); void *get_efi_config_table(efi_guid_t guid); diff --git a/drivers/firmware/efi/libstub/random.c b/drivers/firmware/efi/libstub/random.c index 183dc5cdb8ed..080012e837c3 100644 --- a/drivers/firmware/efi/libstub/random.c +++ b/drivers/firmware/efi/libstub/random.c @@ -67,16 +67,28 @@ efi_status_t efi_random_get_seed(void) efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID; efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW; efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID; + struct linux_efi_random_seed *prev_seed, *seed = NULL; + int prev_seed_size, seed_size = EFI_RANDOM_SEED_SIZE; efi_rng_protocol_t *rng = NULL; - struct linux_efi_random_seed *seed = NULL; efi_status_t status; status = efi_bs_call(locate_protocol, &rng_proto, NULL, (void **)&rng); if (status != EFI_SUCCESS) return status; + /* + * Check whether a seed was provided by a prior boot stage. In that + * case, instead of overwriting it, let's create a new buffer that can + * hold both, and concatenate the existing and the new seeds. + */ + prev_seed = get_efi_config_table(LINUX_EFI_RANDOM_SEED_TABLE_GUID); + if (prev_seed) { + prev_seed_size = min(prev_seed->size, EFI_RANDOM_SEED_SIZE); + seed_size += prev_seed_size; + } + status = efi_bs_call(allocate_pool, EFI_ACPI_RECLAIM_MEMORY, - sizeof(*seed) + EFI_RANDOM_SEED_SIZE, + struct_size(seed, bits, seed_size), (void **)&seed); if (status != EFI_SUCCESS) return status; @@ -95,14 +107,25 @@ efi_status_t efi_random_get_seed(void) if (status != EFI_SUCCESS) goto err_freepool; - seed->size = EFI_RANDOM_SEED_SIZE; + seed->size = seed_size; + if (prev_seed) + memcpy(seed->bits + EFI_RANDOM_SEED_SIZE, prev_seed->bits, + prev_seed_size); + status = efi_bs_call(install_configuration_table, &rng_table_guid, seed); if (status != EFI_SUCCESS) goto err_freepool; + if (prev_seed) { + /* wipe and free the old seed if we managed to install the new one */ + memzero_explicit(prev_seed->bits, prev_seed_size); + efi_bs_call(free_pool, prev_seed); + } return EFI_SUCCESS; err_freepool: + efi_warn("Failed to obtain seed from EFI_RNG_PROTOCOL%s\n", + prev_seed ? ", retaining bootloader supplied seed only" : ""); efi_bs_call(free_pool, seed); return status; } diff --git a/include/linux/efi.h b/include/linux/efi.h index cf96f8d5f15f..69454a7ccc6f 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -1172,8 +1172,6 @@ void efi_check_for_embedded_firmwares(void); static inline void efi_check_for_embedded_firmwares(void) { } #endif -efi_status_t efi_random_get_seed(void); - #define arch_efi_call_virt(p, f, args...) ((p)->f(args)) /*