From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id A7419319847; Wed, 29 Apr 2026 13:52:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777470763; cv=none; b=iZUtlh8xviEElkS1q74MKlIQCGZVAA5yXwFI+krD6HVrMUWtiyUd+mmEtsgjFzIX0y6WOrcQDsg7FxrrbYIjqnt7T/s2+hiadAFj1mYlr8bgy9Fg1/LCVyQpCVeNEQWmTjecesOlA8SJZt1pzbgdsrRJG5bsProxom3u4GnX5QI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777470763; c=relaxed/simple; bh=s0tgitch6tjt2iSC+ew5SbhvP7lh6LqBU7/+wo85gzU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=HInYSyiaKIUycYhSxm5yOK1Zi4nKJAZEWGmiAL4e07vcx1LcrfGjM7Zg6hN8cgBWWdCWhOPHuBu9l/+HRQPypxPjFH/as1tzXePCHJHas+Cfw/TB6s5NkwUGKYmSJVDC/0NVcDlgBdUw7NgZaJsahNaDIg3AB24cAgfXnC8ELW8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=HgLY0Rjc; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="HgLY0Rjc" 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 A548C1C01; Wed, 29 Apr 2026 06:52:33 -0700 (PDT) Received: from [10.57.62.76] (unknown [10.57.62.76]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D42303FB90; Wed, 29 Apr 2026 06:52:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1777470759; bh=s0tgitch6tjt2iSC+ew5SbhvP7lh6LqBU7/+wo85gzU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HgLY0RjcX26UI051X7p0jTvCIxdqYVMTsc8814Yedfgp0bzVK7UFbv8tvL3cLRx6u iDWC3D+nLEDNCb2TZLk5lDi5Udldgc4oVV5EETWkYfWURPnuXnXWyavWHFha+ew//E 2S5LwNp+WnBIoW+zr84x3BSUsI6BHHiVLKyfK5Og= Message-ID: <382872b6-748b-41de-b3f5-728964bbd82a@arm.com> Date: Wed, 29 Apr 2026 15:52:33 +0200 Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 10/15] arm64: Move fixmap page tables to end of kernel image To: Ard Biesheuvel , linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, will@kernel.org, catalin.marinas@arm.com, mark.rutland@arm.com, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , Mike Rapoport , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-hardening@vger.kernel.org References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-27-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260427153416.2103979-27-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 27/04/2026 17:34, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > Move the fixmap page tables out of the BSS section, and place them at > the end of the image, right before the init_pg_dir section where some of > the other statically allocated page tables live. > > These page tables are currently the only data objects in vmlinux that > are meant to be accessed via the kernel image's linear alias, and so > placing them together allows the remainder of the data/bss section to be > remapped read-only or unmapped entirely. > > Signed-off-by: Ard Biesheuvel Reviewed-by: Kevin Brodsky > --- > arch/arm64/kernel/vmlinux.lds.S | 5 +++++ > arch/arm64/mm/fixmap.c | 7 ++++--- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S > index e1ac876200a3..2dca18574619 100644 > --- a/arch/arm64/kernel/vmlinux.lds.S > +++ b/arch/arm64/kernel/vmlinux.lds.S > @@ -353,6 +353,11 @@ SECTIONS > __pi___bss_start = __bss_start; > > . = ALIGN(PAGE_SIZE); > + .fixmap_pgdir : { > + __fixmap_pgdir_start = .; > + *(.fixmap_bss) > + } > + > __pi_init_pg_dir = .; > . += INIT_DIR_SIZE; > __pi_init_pg_end = .; > diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c > index c5c5425791da..b649ea1a46e4 100644 > --- a/arch/arm64/mm/fixmap.c > +++ b/arch/arm64/mm/fixmap.c > @@ -31,9 +31,10 @@ static_assert(NR_BM_PMD_TABLES == 1); > > #define BM_PTE_TABLE_IDX(addr) __BM_TABLE_IDX(addr, PMD_SHIFT) > > -static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __page_aligned_bss; > -static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused; > -static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused; > +#define __fixmap_bss __section(".fixmap_bss") __aligned(PAGE_SIZE) > +static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __fixmap_bss; > +static pmd_t bm_pmd[PTRS_PER_PMD] __fixmap_bss __maybe_unused; > +static pud_t bm_pud[PTRS_PER_PUD] __fixmap_bss __maybe_unused; > > static inline pte_t *fixmap_pte(unsigned long addr) > {