From mboxrd@z Thu Jan 1 00:00:00 1970 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 C87EBC77B77 for ; Mon, 17 Apr 2023 14:02:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230430AbjDQOB6 (ORCPT ); Mon, 17 Apr 2023 10:01:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230416AbjDQOBx (ORCPT ); Mon, 17 Apr 2023 10:01:53 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DCC4E4C39 for ; Mon, 17 Apr 2023 07:00:56 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B0D011691; Mon, 17 Apr 2023 07:01:29 -0700 (PDT) Received: from [10.57.68.227] (unknown [10.57.68.227]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C23473F5A1; Mon, 17 Apr 2023 07:00:44 -0700 (PDT) Message-ID: <37412bd5-9e73-024f-26ab-a351853bc846@arm.com> Date: Mon, 17 Apr 2023 15:00:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH v3 25/60] arm64: head: Clear BSS and the kernel page tables in one go Content-Language: en-US To: Ard Biesheuvel , linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, Catalin Marinas , Will Deacon , Marc Zyngier , Mark Rutland , Anshuman Khandual , Kees Cook References: <20230307140522.2311461-1-ardb@kernel.org> <20230307140522.2311461-26-ardb@kernel.org> From: Ryan Roberts In-Reply-To: <20230307140522.2311461-26-ardb@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/03/2023 14:04, Ard Biesheuvel wrote: > We will move the CPU feature overrides into BSS in a subsequent patch, > and this requires that BSS is zeroed before the feature override > detection code runs. So let's map BSS read-write in the ID map, and zero > it via this mapping. > > Since the kernel page tables are right next to it, and also zeroed via > the ID map, let's drop the separate clear_page_tables() function, and > just zero everything in one go. > > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/kernel/head.S | 33 +++++++------------- > 1 file changed, 11 insertions(+), 22 deletions(-) > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 0fa44b3188c1e204..ade0cb99c8a83a3d 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -177,17 +177,6 @@ SYM_CODE_START_LOCAL(preserve_boot_args) > ret > SYM_CODE_END(preserve_boot_args) > > -SYM_FUNC_START_LOCAL(clear_page_tables) > - /* > - * Clear the init page tables. > - */ > - adrp x0, init_pg_dir > - adrp x1, init_pg_end > - sub x2, x1, x0 > - mov x1, xzr > - b __pi_memset // tail call > -SYM_FUNC_END(clear_page_tables) > - > /* > * Macro to populate page table entries, these entries can be pointers to the next level > * or last level entries pointing to physical memory. > @@ -386,9 +375,9 @@ SYM_FUNC_START_LOCAL(create_idmap) > > map_memory x0, x1, x3, x6, x7, x3, IDMAP_PGD_ORDER, x10, x11, x12, x13, x14, EXTRA_SHIFT > > - /* Remap the kernel page tables r/w in the ID map */ > + /* Remap BSS and the kernel page tables r/w in the ID map */ > adrp x1, _text > - adrp x2, init_pg_dir > + adrp x2, __bss_start > adrp x3, _end > bic x4, x2, #SWAPPER_BLOCK_SIZE - 1 > mov x5, SWAPPER_RW_MMUFLAGS > @@ -489,14 +478,6 @@ SYM_FUNC_START_LOCAL(__primary_switched) > mov x0, x20 > bl set_cpu_boot_mode_flag > > - // Clear BSS > - adr_l x0, __bss_start > - mov x1, xzr > - adr_l x2, __bss_stop > - sub x2, x2, x0 > - bl __pi_memset > - dsb ishst // Make zero page visible to PTW > - > #if VA_BITS > 48 > adr_l x8, vabits_actual // Set this early so KASAN early init > str x25, [x8] // ... observes the correct value > @@ -780,6 +761,15 @@ SYM_FUNC_START_LOCAL(__primary_switch) > adrp x1, reserved_pg_dir > adrp x2, init_idmap_pg_dir > bl __enable_mmu > + > + // Clear BSS > + adrp x0, __bss_start > + mov x1, xzr > + adrp x2, init_pg_end > + sub x2, x2, x0 > + bl __pi_memset > + dsb ishst // Make zero page visible to PTW Is it possible to add an assert somewhere (or at the very least a comment in vmlinux.lds.S) to ensure that nothing gets inserted between the BSS and the page tables? It feels a bit fragile otherwise. I also wonder what's the point in calling __pi_memset() from here? Why not just do it all in C? > + > #ifdef CONFIG_RELOCATABLE > adrp x23, KERNEL_START > and x23, x23, MIN_KIMG_ALIGN - 1 > @@ -794,7 +784,6 @@ SYM_FUNC_START_LOCAL(__primary_switch) > orr x23, x23, x0 // record kernel offset > #endif > #endif > - bl clear_page_tables > bl create_kernel_mapping > > adrp x1, init_pg_dir