From patchwork Tue Aug 22 13:56:51 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 13360847 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 8C357EE49AA for ; Tue, 22 Aug 2023 14:06:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236520AbjHVOGk (ORCPT ); Tue, 22 Aug 2023 10:06:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56770 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236480AbjHVOG3 (ORCPT ); Tue, 22 Aug 2023 10:06:29 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C19EE7E; Tue, 22 Aug 2023 07:05:57 -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 90062657AE; Tue, 22 Aug 2023 14:04:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0D4A7C433B7; Tue, 22 Aug 2023 14:04:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1692713094; bh=3frSXltfyEgjNXyKMr5NRlsNK13A5vKOgV3TE3uJgDA=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=B3UT8vxOVGaVegOI8NaCaSn8giOEs9eVqYN9WX97ni0WSuirae2Tcwh9V7SyMgZ6T hBoE4k6reDxJPgmx3Cwn3HkR7JkFZyk5MvxtVpWegyam3zrGHP7xpZCfle/AbyBs9n 2fGz4Kfiou+GC15IHoFUWi+EyC7Vf9DVuHyz4N8MkdrIlWsFOtpN62T+tryRI4aGCr I/HrbAQ9IP+oTOwY4bOZYvDv6ukz9+/YOxZS28uxnje3CJK9froaQ6HCXtAWDc3VtE pjIjerokOH5e+Y/WLLAnsbY/mvMCAs190YJovQYlvfF8/rVxneKzojc7uBjT9qLwZa 3WydLQ2DDIuJA== From: Mark Brown Date: Tue, 22 Aug 2023 14:56:51 +0100 Subject: [PATCH v5 18/37] arm64/mm: Handle GCS data aborts MIME-Version: 1.0 Message-Id: <20230822-arm64-gcs-v5-18-9ef181dd6324@kernel.org> References: <20230822-arm64-gcs-v5-0-9ef181dd6324@kernel.org> In-Reply-To: <20230822-arm64-gcs-v5-0-9ef181dd6324@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-034f2 X-Developer-Signature: v=1; a=openpgp-sha256; l=5679; i=broonie@kernel.org; h=from:subject:message-id; bh=3frSXltfyEgjNXyKMr5NRlsNK13A5vKOgV3TE3uJgDA=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBk5L/9im1DUi+39LOQU1mpKVEB2F91vv6me+DtJIZ6 hyMd0CWJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZOS//QAKCRAk1otyXVSH0L87B/ 9+wGlX99gOV614aXcVAQd4o9IoMTsg6WepK9KILI3i3olNpP2jqTXj3gggiApp+rXWE7KAMmlz6j4w irvIuu2ZG4x0rPOh/0LMykOrs5HIk0iqEikPtywxTmgtTFXNI29TklzzxZVh6z5kEqnkagFZEGNwl0 zSKaGoMYAbKcBj2b2O252Uvqw7xlRysgV9h/L7spclBPpC2vtpQ3Ttv4iMLGAOssepkgl4Isr12yVa zTfwYvNA0BHyJHb2HCefF86gNry1UqvqYOlyfiywvte40mCogRDKOpPNY7+++SbvX3R/tPzhaGbLJj F0piLbihb2xEc1lY83A4/NLkZJZpCr 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 | 79 +++++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 71 insertions(+), 8 deletions(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 3fe516b32577..42a710981779 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 +644,20 @@ 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, even when the initial operation was a read, as + * a result of upgrading GCS accesses to writes for CoW but + * GCS acceses outside of a GCS must fail. Specifically check + * for this since the mm core isn't able to distinguish + * invalid GCS access from valid ones and will try to resolve + * the fault. + */ + 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 +687,7 @@ 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)) {