From patchwork Mon Jul 31 13:43:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13334725 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 74243C00528 for ; Mon, 31 Jul 2023 13:54:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233049AbjGaNyq (ORCPT ); Mon, 31 Jul 2023 09:54:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43464 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232544AbjGaNxj (ORCPT ); Mon, 31 Jul 2023 09:53:39 -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 2E3851FE2; Mon, 31 Jul 2023 06:52:36 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 9ED4D61138; Mon, 31 Jul 2023 13:52:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A00FC433C9; Mon, 31 Jul 2023 13:52:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690811555; bh=Qk1oAglcSxLTK1OL1yhAbWpcUwaL4dga6Y2wJZdhO9Q=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=bmm91TA/wsaZPU0/8wE66pnfaNWaSJdQZVbqyg3+SSOShzdh0ggMTWS1FEAC8/NxK olDE9hRIYeFcpsqtYbtxT9mAS1hff4uLcoSdxJtguNtWeqQs/V4wxTl570gn1ndoZd eFqbL2i9VUFa5Q7U+ZyKcfdkwFLF/DloaBbZ7+y+DOmQM1cxJzkNGFeo1nVstpdwzM afv2h8zB6/rbNODhkZAd/WU5Nf38ID2g6gff8Dk/bxjUXdKwpIqcLMOE5hNmSb2W98 QatGmPLu2OnW0BCOwH3hZbmmzSODz6YMFJCxHpY5zrzMUJt3DrfnFvdoYANLDanfsF /3ft2eN+AWRgg== From: Mark Brown Date: Mon, 31 Jul 2023 14:43:26 +0100 Subject: [PATCH v3 17/36] arm64/mm: Handle GCS data aborts MIME-Version: 1.0 Message-Id: <20230731-arm64-gcs-v3-17-cddf9f980d98@kernel.org> References: <20230731-arm64-gcs-v3-0-cddf9f980d98@kernel.org> In-Reply-To: <20230731-arm64-gcs-v3-0-cddf9f980d98@kernel.org> To: Catalin Marinas , Will Deacon , Jonathan Corbet , Andrew Morton , Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Arnd Bergmann , Oleg Nesterov , Eric Biederman , Kees Cook , Shuah Khan , "Rick P. Edgecombe" , Deepak Gupta , Ard Biesheuvel , Szabolcs Nagy Cc: "H.J. Lu" , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Mark Brown X-Mailer: b4 0.13-dev-099c9 X-Developer-Signature: v=1; a=openpgp-sha256; l=5613; i=broonie@kernel.org; h=from:subject:message-id; bh=Qk1oAglcSxLTK1OL1yhAbWpcUwaL4dga6Y2wJZdhO9Q=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBkx7whzsGmRy/nIppQQzz6Nju8+l9OjAbrBNJUqFYd 152B5w+JATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZMe8IQAKCRAk1otyXVSH0F8nB/ 9BMXz+0V/6xYz4FAymiTLZwdJwh0jPkGzUNNQ45BqYlDb+x6M9e0xKuUa7+TytDqYicRBsPjo7Klds +Q8TfYSMGxTMvIRDH4iQMdnx4H+KQWvInDHoHh4Jb1lXG469AvJYqKX10Z7foIXDivnKVlhaoE4AXr VPTmdHvr7KQzC6NablbK0C1oy2iyVr36ptY/usiMPdpTv+3AyEuguLBNcpheQBotMdb5R3dHlIqwxO jn9rTcce0v/zhcIanMJv62RMbmz+8h5s97uXmiKyR8E7/LYsJeZ3dO+rl6omtuOk6F1V2bVG96+D31 NQNAplzBhb0gclp1zq2dRARGuU79VQ X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org All GCS operations at EL0 must happen on a page which is marked as having UnprivGCS access, including read operations. If a GCS operation attempts to access a page without this then it will generate a data abort with the GCS bit set in ESR_EL1.ISS2. EL0 may validly generate such faults, for example due to copy on write which will cause the GCS data to be stored in a read only page with no GCS permissions until the actual copy happens. Since UnprivGCS allows both reads and writes to the GCS (though only through GCS operations) we need to ensure that the memory management subsystem handles GCS accesses as writes at all times. Do this by adding FAULT_FLAG_WRITE to any GCS page faults, adding handling to ensure that invalid cases are identfied as such early so the memory management core does not think they will succeed. The core cannot distinguish between VMAs which are generally writeable and VMAs which are only writeable through GCS operations. EL1 may validly write to EL0 GCS for management purposes (eg, while initialising with cap tokens). We also report any GCS faults in VMAs not marked as part of a GCS as access violations, causing a fault to be delivered to userspace if it attempts to do GCS operations outside a GCS. Signed-off-by: Mark Brown --- arch/arm64/mm/fault.c | 78 +++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 70 insertions(+), 8 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 3fe516b32577..ec392207a475 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -494,13 +494,30 @@ static void do_bad_area(unsigned long far, unsigned long esr, } } +/* + * Note: not valid for EL1 DC IVAC, but we never use that such that it + * should fault. EL0 cannot issue DC IVAC (undef). + */ +static bool is_write_abort(unsigned long esr) +{ + return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM); +} + +static bool is_gcs_fault(unsigned long esr) +{ + if (!esr_is_data_abort(esr)) + return false; + + return ESR_ELx_ISS2(esr) & ESR_ELx_GCS; +} + #define VM_FAULT_BADMAP ((__force vm_fault_t)0x010000) #define VM_FAULT_BADACCESS ((__force vm_fault_t)0x020000) static vm_fault_t __do_page_fault(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long addr, unsigned int mm_flags, unsigned long vm_flags, - struct pt_regs *regs) + unsigned long esr, struct pt_regs *regs) { /* * Ok, we have a good vm_area for this memory access, so we can handle @@ -510,6 +527,26 @@ static vm_fault_t __do_page_fault(struct mm_struct *mm, */ if (!(vma->vm_flags & vm_flags)) return VM_FAULT_BADACCESS; + + if (vma->vm_flags & VM_SHADOW_STACK) { + /* + * Writes to a GCS must either be generated by a GCS + * operation or be from EL1. + */ + if (is_write_abort(esr) && + !(is_gcs_fault(esr) || is_el1_data_abort(esr))) + return VM_FAULT_BADACCESS; + } else { + /* + * GCS faults should never happen for pages that are + * not part of a GCS and the operation being attempted + * can never succeed. + */ + if (is_gcs_fault(esr)) + return VM_FAULT_BADACCESS; + } + + return handle_mm_fault(vma, addr, mm_flags, regs); } @@ -518,13 +555,18 @@ static bool is_el0_instruction_abort(unsigned long esr) return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_LOW; } -/* - * Note: not valid for EL1 DC IVAC, but we never use that such that it - * should fault. EL0 cannot issue DC IVAC (undef). - */ -static bool is_write_abort(unsigned long esr) +static bool is_invalid_el0_gcs_access(struct vm_area_struct *vma, u64 esr) { - return (esr & ESR_ELx_WNR) && !(esr & ESR_ELx_CM); + if (!system_supports_gcs()) + return false; + if (likely(!(vma->vm_flags & VM_SHADOW_STACK))) { + if (is_gcs_fault(esr)) + return true; + return false; + } + if (is_gcs_fault(esr)) + return false; + return is_write_abort(esr); } static int __kprobes do_page_fault(unsigned long far, unsigned long esr, @@ -573,6 +615,13 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, /* If EPAN is absent then exec implies read */ if (!cpus_have_const_cap(ARM64_HAS_EPAN)) vm_flags |= VM_EXEC; + /* + * Upgrade read faults to write faults, GCS reads must + * occur on a page marked as GCS so we need to trigger + * copy on write always. + */ + if (is_gcs_fault(esr)) + mm_flags |= FAULT_FLAG_WRITE; } if (is_ttbr0_addr(addr) && is_el1_permission_fault(addr, esr, regs)) { @@ -595,6 +644,19 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, if (!vma) goto lock_mmap; + /* + * We get legitimate write faults for GCS pages from GCS + * operations and from EL1 writes to EL0 pages but just plain + * EL0 writes are invalid. Specifically check for this since + * as a result of upgrading read faults to write faults for + * CoW the mm core isn't able to distinguish these invalid + * writes. + */ + if (is_invalid_el0_gcs_access(vma, esr)) { + vma_end_read(vma); + goto lock_mmap; + } + if (!(vma->vm_flags & vm_flags)) { vma_end_read(vma); goto lock_mmap; @@ -624,7 +686,7 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long esr, goto done; } - fault = __do_page_fault(mm, vma, addr, mm_flags, vm_flags, regs); + fault = __do_page_fault(mm, vma, addr, mm_flags, vm_flags, esr, regs); /* Quick path to respond to signals */ if (fault_signal_pending(fault, regs)) {