From patchwork Mon Oct 9 12:08:53 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Brown X-Patchwork-Id: 731241 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 D2DFCE95A9C for ; Mon, 9 Oct 2023 12:15:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376301AbjJIMO6 (ORCPT ); Mon, 9 Oct 2023 08:14:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376343AbjJIMOB (ORCPT ); Mon, 9 Oct 2023 08:14:01 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14B3ED48; Mon, 9 Oct 2023 05:12:54 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B76BC433CA; Mon, 9 Oct 2023 12:12:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1696853573; bh=U1l0Oub8DGXeBnKIw3SOas1EfStDVYy3cBry+b4y2KY=; h=From:Date:Subject:References:In-Reply-To:To:Cc:From; b=nidKzb6KjaupAUNRQ7cqd5mxL//1PZ7Zr0fs9cUxP2Sqp3dUEAlrgp4LoAr30o55W U710+3rdLZ6ZzwuKUFNq/3ntxIVKLkn5Jp3FYJJm+pvRYVzp/jJUgl7V2Yz1NgIShJ PV9n9kGvXyWc6fCUyE/z8OmzA6pXnJ+ZP2i9eETmkNDUMu8lIrog4PNrjVYVbd1/tV o8w6eNqVhOf9GYYIjrWmGkApgNbk+6ArtRI/AwjFPMBBUz3+W2gE+vMZrCvgFrig8Z oM5dG9qkqa7qk4KCOugY5ojML/qLd+Hmu0zdL5OTwKi+A0NGUy01Ur8afAbwIxEHgX QxYQH47PfwqGA== From: Mark Brown Date: Mon, 09 Oct 2023 13:08:53 +0100 Subject: [PATCH v6 19/38] arm64/mm: Handle GCS data aborts MIME-Version: 1.0 Message-Id: <20231009-arm64-gcs-v6-19-78e55deaa4dd@kernel.org> References: <20231009-arm64-gcs-v6-0-78e55deaa4dd@kernel.org> In-Reply-To: <20231009-arm64-gcs-v6-0-78e55deaa4dd@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 , Florian Weimer , Christian Brauner , 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-0438c X-Developer-Signature: v=1; a=openpgp-sha256; l=5679; i=broonie@kernel.org; h=from:subject:message-id; bh=U1l0Oub8DGXeBnKIw3SOas1EfStDVYy3cBry+b4y2KY=; b=owEBbQGS/pANAwAKASTWi3JdVIfQAcsmYgBlI+2gzvC6/uRznZqzKfe/TGEH5CxDCcE+V/5gJRNL +1aTQbKJATMEAAEKAB0WIQSt5miqZ1cYtZ/in+ok1otyXVSH0AUCZSPtoAAKCRAk1otyXVSH0LU/B/ 0Ydu7yT5bbYSp6sxq/2tFGycuTvi9kpwlvDefRWYOXy0CmFYrhj7uu3+ALG2+fh7QzI3l5YiwjNw7t l1w03bBgoR9OW4hW4J94aGDQrIt9ZgpRP0eROtCgquKr4tFxdD+c/BVIumziARnNX8LU4HKUb1oe/5 WrND2lz3GpPjyo/ilirjaB/GhzLquoVwzOqINgs00dIkV9jp0cfBZqdSQVopTDVeNOB7lKhRJJIRg/ Bn9VJkcivmoT36Bxq6ij2Wdd2U0mhQNPQkxxpeFhUJvmxQ0Tgljc1tOOSl2W/HGw5D14eunK2/jhmh +SrtxgjjbNtrL/kg+/sLkqxk2hVxc1 X-Developer-Key: i=broonie@kernel.org; a=openpgp; fpr=3F2568AAC26998F9E813A1C5C3F436CA30F5D8EB Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@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 2e5d1e238af9..9dd143df4483 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)) { @@ -594,6 +643,20 @@ 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; @@ -623,7 +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)) {