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 AA97DC433F5 for ; Tue, 1 Feb 2022 11:44:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237358AbiBALoO (ORCPT ); Tue, 1 Feb 2022 06:44:14 -0500 Received: from foss.arm.com ([217.140.110.172]:33770 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233560AbiBALoM (ORCPT ); Tue, 1 Feb 2022 06:44:12 -0500 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 8C457113E; Tue, 1 Feb 2022 03:44:11 -0800 (PST) Received: from entos-thunderx2-desktop.shanghai.arm.com (entos-thunderx2-desktop.shanghai.arm.com [10.169.212.232]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id A64993F73B; Tue, 1 Feb 2022 03:44:07 -0800 (PST) From: Jianyong Wu To: catalin.marinas@arm.com, will@kernel.org, anshuman.khandual@arm.com, akpm@linux-foundation.org, david@redhat.com, ardb@kernel.org Cc: quic_qiancai@quicinc.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, gshan@redhat.com, justin.he@arm.com, jianyong.wu@arm.com, nd@arm.com Subject: [PATCH] [PATCH v4] arm64/mm: avoid fixmap race condition when create pud mapping Date: Tue, 1 Feb 2022 19:44:00 +0800 Message-Id: <20220201114400.56885-1-jianyong.wu@arm.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The 'fixmap' is a global resource and is used recursively by create pud mapping(), leading to a potential race condition in the presence of a concurrent call to alloc_init_pud(): kernel_init thread virtio-mem workqueue thread ================== =========================== alloc_init_pud(...) alloc_init_pud(...) pudp = pud_set_fixmap_offset(...) pudp = pud_set_fixmap_offset(...) READ_ONCE(*pudp) pud_clear_fixmap(...) READ_ONCE(*pudp) // CRASH! As kernel may sleep during creating pud mapping, introduce a mutex lock to serialise use of the fixmap entries by alloc_init_pud(). However, there is no need for locking in early boot stage and it doesn't work well with KASLR enabled when early boot. So, enable lock when system_state doesn't equal to "SYSTEM_BOOTING". Signed-off-by: Jianyong Wu --- Change log: from v3 to v4: conditionally enable lock as we doesn't need lock when early boot. from v2 to v3: change spin lock to mutex lock as kernel may sleep when create pud map. --- arch/arm64/mm/mmu.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index acfae9b41cc8..1681430ecab7 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -63,6 +63,7 @@ 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; static DEFINE_SPINLOCK(swapper_pgdir_lock); +static DEFINE_MUTEX(fixmap_lock); void set_swapper_pgd(pgd_t *pgdp, pgd_t pgd) { @@ -329,6 +330,12 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } BUG_ON(p4d_bad(p4d)); + /* + * No need for locking during early boot. And it doesn't work as + * expected with KASLR enabled. + */ + if (system_state != SYSTEM_BOOTING) + mutex_lock(&fixmap_lock); pudp = pud_set_fixmap_offset(p4dp, addr); do { pud_t old_pud = READ_ONCE(*pudp); @@ -359,6 +366,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end, } while (pudp++, addr = next, addr != end); pud_clear_fixmap(); + if (system_state != SYSTEM_BOOTING) + mutex_unlock(&fixmap_lock); } static void __create_pgd_mapping(pgd_t *pgdir, phys_addr_t phys, -- 2.17.1