From nobody Fri Dec 19 01:10:38 2025 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 71FEEC001E0 for ; Mon, 23 Oct 2023 14:44:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233801AbjJWOoO (ORCPT ); Mon, 23 Oct 2023 10:44:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50008 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233698AbjJWOnt (ORCPT ); Mon, 23 Oct 2023 10:43:49 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7BC1426A4 for ; Mon, 23 Oct 2023 07:42:29 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 17B541FE26; Mon, 23 Oct 2023 14:42:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1698072148; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iKEUG9SHB6x+trsiRcHBTizDjwB2rC51Fj16Z+SAh18=; b=ZiOCAb8terQeWFu0Gp5FoprPiJsiQ3xSPzR2zvqOyloHHkz2+BgO9CTMpDQIG8xptvpcl6 AUUi8sw6p9HMOn+Szbj2g/ggFZcMNFQ+9rqo6xDw69lSkJ4N7zQDTF0IrZs0Es9DXdDyBN hIO56oQg5WXvA4kFIATudttPc18+x+Y= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id E62B5139C2; Mon, 23 Oct 2023 14:42:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id mLeKNlOGNmXLdgAAMHmgww (envelope-from ); Mon, 23 Oct 2023 14:42:27 +0000 From: Andrea della Porta To: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: nik.borisov@suse.com, arnd@arndb.de, mark.rutland@arm.com, Andrea della Porta Subject: [PATCH v2 4/4] arm64: Make Aarch32 support boot time configurable Date: Mon, 23 Oct 2023 16:42:23 +0200 Message-ID: X-Mailer: git-send-email 2.41.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Authentication-Results: smtp-out2.suse.de; none X-Spamd-Result: default: False [-5.70 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; BAYES_HAM(-3.00)[100.00%]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; R_MISSING_CHARSET(2.50)[]; MIME_GOOD(-0.10)[text/plain]; BROKEN_CONTENT_TYPE(1.50)[]; REPLY(-4.00)[]; NEURAL_HAM_LONG(-3.00)[-1.000]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; NEURAL_HAM_SHORT(-1.00)[-1.000]; RCPT_COUNT_SEVEN(0.00)[8]; MID_CONTAINS_FROM(1.00)[]; FORGED_SENDER(0.30)[andrea.porta@suse.com,aporta@suse.de]; MIME_TRACE(0.00)[0:+]; RCVD_COUNT_TWO(0.00)[2]; FROM_NEQ_ENVFROM(0.10)[andrea.porta@suse.com,aporta@suse.de]; RCVD_TLS_ALL(0.00)[] Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Distributions would like to reduce their attack surface as much as possible but at the same time they'd want to retain flexibility to cater to a variety of legacy software. This stems from the conjecture that compat layer is likely rarely tested and could have latent security bugs. Ideally distributions will set their default policy and also give users the ability to override it as appropriate. To enable this use case, introduce CONFIG_AARCH32_SUPPORT_DEFAULT_DISABLED compile time option, which controls whether 32bit processes/exceptions should be allowed or not. This option is aimed mainly at distributions to set their preferred default behavior in their kernels. To allow users to override the distro's policy, introduce the 'allow_32bit_el0' parameter which allows overriding CONFIG_AARCH32_SUPPORT_DEFAULT_DISABLED state at boot time. Signed-off-by: Andrea della Porta --- Documentation/admin-guide/kernel-parameters.txt | 7 +++++++ arch/arm64/Kconfig | 9 +++++++++ arch/arm64/kernel/entry-common.c | 8 +++++++- 3 files changed, 23 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 0a1731a0f0ef..9752c4640bd7 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1,3 +1,10 @@ + allow_32bit_el0=3D [ARM64] + Format: + When true, allows loading 32-bit programs and executing + 32-bit syscalls and exceptions, essentially overriding + AARCH32_SUPPORT_DEFAULT_DISABLED at boot time. when false, + unconditionally disables AARCH32 support. + acpi=3D [HW,ACPI,X86,ARM64,RISCV64] Advanced Configuration and Power Interface Format: { force | on | off | strict | noirq | rsdt | diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index b10515c0200b..c8e1b3535018 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1725,6 +1725,15 @@ config SETEND_EMULATION If unsure, say Y endif # ARMV8_DEPRECATED =20 +config AARCH32_SUPPORT_DEFAULT_DISABLED + bool "Aarch32 support disabled by default" + default n + depends on COMPAT + help + Make Aarch32 support disabled by default. This prevents loading 32-bit + processes and access to 32-bit syscalls and exceptions. + + If unsure, leave it to its default value. endif # COMPAT =20 menu "ARMv8.1 architectural features" diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-com= mon.c index 32761760d9dd..7698057ef4ce 100644 --- a/arch/arm64/kernel/entry-common.c +++ b/arch/arm64/kernel/entry-common.c @@ -897,7 +897,13 @@ asmlinkage void noinstr el0t_32_error_handler(struct p= t_regs *regs) __el0_error_handler_common(regs); } =20 -bool __aarch32_enabled __ro_after_init =3D true; +bool __aarch32_enabled __ro_after_init =3D !IS_ENABLED(CONFIG_AARCH32_SUPP= ORT_DEFAULT_DISABLED); + +static int aarch32_support_override_cmdline(char *arg) +{ + return kstrtobool(arg, &__aarch32_enabled); +} +early_param("allow_32bit_el0", aarch32_support_override_cmdline); #else /* CONFIG_COMPAT */ UNHANDLED(el0t, 32, sync) UNHANDLED(el0t, 32, irq) --=20 2.35.3