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 X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 14F57C43381 for ; Tue, 16 Mar 2021 15:15:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DABB2650FE for ; Tue, 16 Mar 2021 15:15:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236134AbhCPPOx (ORCPT ); Tue, 16 Mar 2021 11:14:53 -0400 Received: from mga01.intel.com ([192.55.52.88]:38747 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237762AbhCPPLe (ORCPT ); Tue, 16 Mar 2021 11:11:34 -0400 IronPort-SDR: +EFIZbDJtBQY6I0EPSJMklGyBwRIneCCSPfxNaGHGjY5UiT/vDtsPQNluDXWPlvz09Gj1DzEK5 X0ug/htNxsBg== X-IronPort-AV: E=McAfee;i="6000,8403,9924"; a="209212693" X-IronPort-AV: E=Sophos;i="5.81,251,1610438400"; d="scan'208";a="209212693" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Mar 2021 08:11:34 -0700 IronPort-SDR: Wz2n3AD68N1URJgjslWA+rFE3RRucgMj7sNXFDyCxldTpAVIVoRtsvOBx/CEuuIDQITXC/4SF/ lDytDm798Bng== X-IronPort-AV: E=Sophos;i="5.81,251,1610438400"; d="scan'208";a="405570343" Received: from yyu32-desk.sc.intel.com ([143.183.136.146]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Mar 2021 08:11:34 -0700 From: Yu-cheng Yu To: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Haitao Huang Cc: Yu-cheng Yu Subject: [PATCH v23 28/28] mm: Introduce PROT_SHSTK for shadow stack Date: Tue, 16 Mar 2021 08:10:54 -0700 Message-Id: <20210316151054.5405-29-yu-cheng.yu@intel.com> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20210316151054.5405-1-yu-cheng.yu@intel.com> References: <20210316151054.5405-1-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There are three possible options to create a shadow stack allocation API: an arch_prctl, a new syscall, or adding PROT_SHSTK to mmap()/mprotect(). Each has its advantages and compromises. An arch_prctl() is the least intrusive. However, the existing x86 arch_prctl() takes only two parameters. Multiple parameters must be passed in a memory buffer. There is a proposal to pass more parameters in registers [1], but no active discussion on that. A new syscall minimizes compatibility issues and offers an extensible frame work to other architectures, but this will likely result in some overlap of mmap()/mprotect(). The introduction of PROT_SHSTK to mmap()/mprotect() takes advantage of existing APIs. The x86-specific PROT_SHSTK is translated to VM_SHSTK and a shadow stack mapping is created without reinventing the wheel. There are potential pitfalls though. The most obvious one would be using this as a bypass to shadow stack protection. However, the attacker would have to get to the syscall first. [1] https://lore.kernel.org/lkml/20200828121624.108243-1-hjl.tools@gmail.com/ Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook --- arch/x86/include/asm/mman.h | 57 +++++++++++++++++++++++++++++++- arch/x86/include/uapi/asm/mman.h | 1 + include/linux/mm.h | 1 + mm/mmap.c | 8 ++++- 4 files changed, 65 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/mman.h b/arch/x86/include/asm/mman.h index 629f6c81263a..bd94e30b5d34 100644 --- a/arch/x86/include/asm/mman.h +++ b/arch/x86/include/asm/mman.h @@ -20,11 +20,66 @@ ((vm_flags) & VM_PKEY_BIT2 ? _PAGE_PKEY_BIT2 : 0) | \ ((vm_flags) & VM_PKEY_BIT3 ? _PAGE_PKEY_BIT3 : 0)) -#define arch_calc_vm_prot_bits(prot, key) ( \ +#define pkey_vm_prot_bits(prot, key) ( \ ((key) & 0x1 ? VM_PKEY_BIT0 : 0) | \ ((key) & 0x2 ? VM_PKEY_BIT1 : 0) | \ ((key) & 0x4 ? VM_PKEY_BIT2 : 0) | \ ((key) & 0x8 ? VM_PKEY_BIT3 : 0)) +#else +#define pkey_vm_prot_bits(prot, key) (0) +#endif + +static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot, + unsigned long pkey) +{ + unsigned long vm_prot_bits = pkey_vm_prot_bits(prot, pkey); + + if (!(prot & PROT_WRITE) && (prot & PROT_SHSTK)) + vm_prot_bits |= VM_SHSTK; + + return vm_prot_bits; +} + +#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey) + +#ifdef CONFIG_X86_CET +static inline bool arch_validate_prot(unsigned long prot, unsigned long addr) +{ + unsigned long valid = PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM; + + if (prot & ~(valid | PROT_SHSTK)) + return false; + + if (prot & PROT_SHSTK) { + struct vm_area_struct *vma; + + if (!current->thread.cet.shstk_size) + return false; + + /* + * A shadow stack mapping is indirectly writable by only + * the CALL and WRUSS instructions, but not other write + * instructions). PROT_SHSTK and PROT_WRITE are mutually + * exclusive. + */ + if (prot & PROT_WRITE) + return false; + + vma = find_vma(current->mm, addr); + if (!vma) + return false; + + /* + * Shadow stack cannot be backed by a file or shared. + */ + if (vma->vm_file || (vma->vm_flags & VM_SHARED)) + return false; + } + + return true; +} + +#define arch_validate_prot arch_validate_prot #endif #endif /* _ASM_X86_MMAN_H */ diff --git a/arch/x86/include/uapi/asm/mman.h b/arch/x86/include/uapi/asm/mman.h index 3ce1923e6ed9..39bb7db344a6 100644 --- a/arch/x86/include/uapi/asm/mman.h +++ b/arch/x86/include/uapi/asm/mman.h @@ -4,6 +4,7 @@ #define MAP_32BIT 0x40 /* only give out 32bit addresses */ +#define PROT_SHSTK 0x10 /* shadow stack pages */ #include diff --git a/include/linux/mm.h b/include/linux/mm.h index e178be052419..40c4b0fe7cc4 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -342,6 +342,7 @@ extern unsigned int kobjsize(const void *objp); #if defined(CONFIG_X86) # define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */ +# define VM_ARCH_CLEAR VM_SHSTK #elif defined(CONFIG_PPC) # define VM_SAO VM_ARCH_1 /* Strong Access Ordering (powerpc) */ #elif defined(CONFIG_PARISC) diff --git a/mm/mmap.c b/mm/mmap.c index 99077171010b..934cb3cbe952 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1481,6 +1481,12 @@ unsigned long do_mmap(struct file *file, unsigned long addr, struct inode *inode = file_inode(file); unsigned long flags_mask; + /* + * Call stack cannot be backed by a file. + */ + if (vm_flags & VM_SHSTK) + return -EINVAL; + if (!file_mmap_ok(file, inode, pgoff, len)) return -EOVERFLOW; @@ -1545,7 +1551,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr, } else { switch (flags & MAP_TYPE) { case MAP_SHARED: - if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP)) + if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP|VM_SHSTK)) return -EINVAL; /* * Ignore pgoff. -- 2.21.0