From patchwork Fri May 31 23:31:58 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sean Christopherson X-Patchwork-Id: 10971027 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 59C44112C for ; Fri, 31 May 2019 23:33:05 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 4BBCC28D9E for ; Fri, 31 May 2019 23:33:05 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 3FEF228DA3; Fri, 31 May 2019 23:33:05 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A3E2228D9E for ; Fri, 31 May 2019 23:33:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726911AbfEaXcj (ORCPT ); Fri, 31 May 2019 19:32:39 -0400 Received: from mga07.intel.com ([134.134.136.100]:59347 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726883AbfEaXci (ORCPT ); Fri, 31 May 2019 19:32:38 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga105.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 May 2019 16:32:31 -0700 X-ExtLoop1: 1 Received: from sjchrist-coffee.jf.intel.com ([10.54.74.36]) by orsmga008.jf.intel.com with ESMTP; 31 May 2019 16:32:31 -0700 From: Sean Christopherson To: Jarkko Sakkinen Cc: Andy Lutomirski , Cedric Xing , Stephen Smalley , James Morris , "Serge E . Hallyn" , LSM List , Paul Moore , Eric Paris , selinux@vger.kernel.org, Jethro Beekman , Dave Hansen , Thomas Gleixner , Linus Torvalds , LKML , X86 ML , linux-sgx@vger.kernel.org, Andrew Morton , nhorman@redhat.com, npmccallum@redhat.com, Serge Ayoun , Shay Katz-zamir , Haitao Huang , Andy Shevchenko , Kai Svahn , Borislav Petkov , Josh Triplett , Kai Huang , David Rientjes , William Roberts , Philip Tricca Subject: [RFC PATCH 8/9] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX Date: Fri, 31 May 2019 16:31:58 -0700 Message-Id: <20190531233159.30992-9-sean.j.christopherson@intel.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190531233159.30992-1-sean.j.christopherson@intel.com> References: <20190531233159.30992-1-sean.j.christopherson@intel.com> MIME-Version: 1.0 Sender: linux-sgx-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-sgx@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP enclave_load() is roughly analogous to the existing file_mprotect(). Due to the nature of SGX and its Enclave Page Cache (EPC), all enclave VMAs are backed by a single file, i.e. /dev/sgx/enclave, that must be MAP_SHARED. Furthermore, all enclaves need read, write and execute VMAs. As a result, file_mprotect() does not provide any meaningful security for enclaves since an LSM can only deny/grant access to the EPC as a whole. security_enclave_load() is called when SGX is first loading an enclave page, i.e. copying a page from normal memory into the EPC. The notable difference from file_mprotect() is the allowed_prot parameter, which is essentially an SGX-specific version of a VMA's MAY_{READ,WRITE,EXEC} flags. The purpose of allowed_prot is to enable checks such as SELinux's FILE__EXECMOD permission without having to track and update VMAs across multiple mm structs, i.e. SGX can ensure userspace doesn't overstep its bounds simply by restricting an enclave VMA's protections by vetting what is maximally allowed during build time. An alternative to the allowed_prot approach would be to use an enclave's SIGSTRUCT (a smallish structure that can uniquely identify an enclave) as a proxy for the enclave. For example, SGX could take and hold a reference to the file containing the SIGSTRUCT (if it's in a file) and call security_enclave_load() during mprotect(). While the SIGSTRUCT approach would provide better precision, the actual value added was deemed to be negligible. On the other hand, pinning a file for the lifetime of the enclave is ugly, and essentially caching LSM policies in each page's allowed_prot avoids having to make an extra LSM upcall during mprotect(). Note, extensive discussion yielded no sane alternative to some form of SGX specific LSM hook[1]. [1] https://lkml.kernel.org/r/CALCETrXf8mSK45h7sTK5Wf+pXLVn=Bjsc_RLpgO-h-qdzBRo5Q@mail.gmail.com Signed-off-by: Sean Christopherson --- arch/x86/kernel/cpu/sgx/driver/ioctl.c | 14 +++++++++----- include/linux/lsm_hooks.h | 16 ++++++++++++++++ include/linux/security.h | 2 ++ security/security.c | 8 ++++++++ 4 files changed, 35 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c index 5f71be7cbb01..260417ecbcff 100644 --- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c +++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c @@ -8,6 +8,7 @@ #include #include #include +#include #include #include #include @@ -580,21 +581,24 @@ static int sgx_encl_page_protect(unsigned long src, unsigned long prot, unsigned long *allowed_prot) { struct vm_area_struct *vma; + int ret = 0; - if (!(*allowed_prot & VM_EXEC)) + if (!(*allowed_prot & VM_EXEC) && !IS_ENABLED(CONFIG_SECURITY)) goto do_check; down_read(¤t->mm->mmap_sem); vma = find_vma(current->mm, src); if (!vma || (vma->vm_file && path_noexec(&vma->vm_file->f_path))) *allowed_prot &= ~VM_EXEC; +#ifdef CONFIG_SECURITY + ret = security_enclave_load(vma, prot, allowed_prot); +#endif up_read(¤t->mm->mmap_sem); do_check: - if (prot & ~*allowed_prot) - return -EACCES; - - return 0; + if (!ret && (prot & ~*allowed_prot)) + ret = -EACCES; + return ret; } static int sgx_encl_add_page(struct sgx_encl *encl, unsigned long addr, diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 47f58cfb6a19..0562775424a0 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -1446,6 +1446,14 @@ * @bpf_prog_free_security: * Clean up the security information stored inside bpf prog. * + * Security hooks for Intel SGX enclaves. + * + * @enclave_load: + * On success, returns 0 and optionally adjusts @allowed_prot + * @vma: the source memory region of the enclave page being loaded. + * @prot: the initial protection of the enclave page. + * @allowed_prot: the maximum protections of the enclave page. + * Return 0 if permission is granted. */ union security_list_options { int (*binder_set_context_mgr)(struct task_struct *mgr); @@ -1807,6 +1815,11 @@ union security_list_options { int (*bpf_prog_alloc_security)(struct bpf_prog_aux *aux); void (*bpf_prog_free_security)(struct bpf_prog_aux *aux); #endif /* CONFIG_BPF_SYSCALL */ + +#ifdef CONFIG_INTEL_SGX + int (*enclave_load)(struct vm_area_struct *vma, unsigned long prot, + unsigned long *allowed_prot); +#endif /* CONFIG_INTEL_SGX */ }; struct security_hook_heads { @@ -2046,6 +2059,9 @@ struct security_hook_heads { struct hlist_head bpf_prog_alloc_security; struct hlist_head bpf_prog_free_security; #endif /* CONFIG_BPF_SYSCALL */ +#ifdef CONFIG_INTEL_SGX + struct hlist_head enclave_load; +#endif /* CONFIG_INTEL_SGX */ } __randomize_layout; /* diff --git a/include/linux/security.h b/include/linux/security.h index 659071c2e57c..2f7925eeef7e 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -392,6 +392,8 @@ void security_inode_invalidate_secctx(struct inode *inode); int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen); int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen); int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen); +int security_enclave_load(struct vm_area_struct *vma, unsigned long prot, + unsigned long *allowed_prot); #else /* CONFIG_SECURITY */ static inline int call_lsm_notifier(enum lsm_event event, void *data) diff --git a/security/security.c b/security/security.c index 613a5c00e602..07ed6763571e 100644 --- a/security/security.c +++ b/security/security.c @@ -2359,3 +2359,11 @@ void security_bpf_prog_free(struct bpf_prog_aux *aux) call_void_hook(bpf_prog_free_security, aux); } #endif /* CONFIG_BPF_SYSCALL */ + +#ifdef CONFIG_INTEL_SGX +int security_enclave_load(struct vm_area_struct *vma, unsigned long prot, + unsigned long *allowed_prot) +{ + return call_int_hook(enclave_load, 0, vma, prot, allowed_prot); +} +#endif /* CONFIG_INTEL_SGX */