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=-13.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1AFA3C43462 for ; Tue, 11 May 2021 11:48:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E92826143C for ; Tue, 11 May 2021 11:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231530AbhEKLuB (ORCPT ); Tue, 11 May 2021 07:50:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40502 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230400AbhEKLuB (ORCPT ); Tue, 11 May 2021 07:50:01 -0400 Received: from mail-lf1-x130.google.com (mail-lf1-x130.google.com [IPv6:2a00:1450:4864:20::130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B2847C061760 for ; Tue, 11 May 2021 04:48:53 -0700 (PDT) Received: by mail-lf1-x130.google.com with SMTP id i9so21635947lfe.13 for ; Tue, 11 May 2021 04:48:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=OxdoaKPOQuUdKzkVcLxQZyyXBdgyHiRS3tUGaZINUts=; b=pu5+cwzEKuzc6EKXsqJ7EaWSkxB7rCn6gNQ30VMCpZCLAPn9ir6RnzaGipRTyxVm+K pSnBAdAG4NNgwEkwdQTxjhsKwtxFqJ99SznjFTuhezxvdIHgaI6BBv3p+8p0XsHszG+V RQaHASxm9Et0cxJy0qUKzFBFViubxluBaNVVg45aQybB/7wIbjaw1IMMvZVohB06z+O9 3s8uL1JLKzVYvB1RZkPBju2l4gzFHKeK2tL7LkbfaYQ8lrlvI566AMHvwhvFVbRBso9Z tDguC2zPMdW7HGa4bDpl5xh98LNl9ydjJwxQSDPvWhWqmX6vFAPsI2/5z5P21MbGsP3t 13iA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=OxdoaKPOQuUdKzkVcLxQZyyXBdgyHiRS3tUGaZINUts=; b=LZbGzgBbloluCtaAtoBk5z2MbD1/0RaUqTUfvv++UcortXjvJXghNfqr5aEFNaaG0R YrmPPQVBEgjaP4ymYmxmd7Z7D+BsCgZeG41R8f02gRSIyLsuBbSp0kzlO631xeQc6Q+C nWPHp6bxY9KXi8cDA6F7Q1J/vDwTdT/YiaT/ZjBqG64I4s3V71d4Jyy1gRb6HwceU2Ma wVpkxALhni2Krbpo3N78sw1UwrKBBW4o5DYb7Tlc/8kSgza9BDk27FieRixdXktkoXRl QimBATymZzyHhTmfI8Q4RksimUwOeJfTtyGKe/k0oRsymgEffG0CJJ+ExHwSUBdIdOYT 8l3g== X-Gm-Message-State: AOAM530aAVpi/v15TqA5B3LEWF1ev9xkRmhCPRlXwlzt+3k5X5SN9okF TQCr82LGUnCRUtpU7St3jvBpEg== X-Google-Smtp-Source: ABdhPJydVEzMQLCZSWLjQHEgnr+jpAeuIOL0TV29D90uqoPSgdYZuwn5zByK9Fy6Y0UQztu1N5pypA== X-Received: by 2002:a05:6512:b8e:: with SMTP id b14mr20299532lfv.404.1620733732151; Tue, 11 May 2021 04:48:52 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id x19sm2604242lfa.22.2021.05.11.04.48.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 11 May 2021 04:48:51 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 40BD0102615; Tue, 11 May 2021 14:48:52 +0300 (+03) Date: Tue, 11 May 2021 14:48:52 +0300 From: "Kirill A. Shutemov" To: Yu-cheng Yu Cc: 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 , "Kirill A . Shutemov" Subject: Re: [PATCH v26 30/30] mm: Introduce PROT_SHADOW_STACK for shadow stack Message-ID: <20210511114852.5wm6a5z72xjlqc4c@box> References: <20210427204315.24153-1-yu-cheng.yu@intel.com> <20210427204315.24153-31-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210427204315.24153-31-yu-cheng.yu@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Apr 27, 2021 at 01:43:15PM -0700, Yu-cheng Yu wrote: > There are three possible options to create a shadow stack allocation API: > an arch_prctl, a new syscall, or adding PROT_SHADOW_STACK to mmap() and > 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_SHADOW_STACK to mmap()/mprotect() takes advantage > of existing APIs. The x86-specific PROT_SHADOW_STACK is translated to > VM_SHADOW_STACK 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 > Cc: Kees Cook > Cc: Kirill A. Shutemov > --- > v26: > - Change PROT_SHSTK to PROT_SHADOW_STACK. > - Remove (vm_flags & VM_SHARED) check, since it is covered by > !vma_is_anonymous(). > > v24: > - Update arch_calc_vm_prot_bits(), leave PROT* checking to > arch_validate_prot(). > - Update arch_validate_prot(), leave vma flags checking to > arch_validate_flags(). > - Add arch_validate_flags(). > > arch/x86/include/asm/mman.h | 60 +++++++++++++++++++++++++++++++- > arch/x86/include/uapi/asm/mman.h | 2 ++ > include/linux/mm.h | 1 + > 3 files changed, 62 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/mman.h b/arch/x86/include/asm/mman.h > index 629f6c81263a..fbb90f1b02c0 100644 > --- a/arch/x86/include/asm/mman.h > +++ b/arch/x86/include/asm/mman.h > @@ -20,11 +20,69 @@ > ((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_SHADOW_STACK) > + vm_prot_bits |= VM_SHADOW_STACK; > + > + return vm_prot_bits; > +} > + > +#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey) > + > +#ifdef CONFIG_X86_SHADOW_STACK > +static inline bool arch_validate_prot(unsigned long prot, unsigned long addr) > +{ > + unsigned long valid = PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | > + PROT_SHADOW_STACK; > + > + if (prot & ~valid) > + return false; > + > + if (prot & PROT_SHADOW_STACK) { > + 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_SHADOW_STACK and PROT_WRITE are > + * mutually exclusive. > + */ > + if (prot & PROT_WRITE) > + return false; > + } > + > + return true; > +} > + > +#define arch_validate_prot arch_validate_prot > + > +static inline bool arch_validate_flags(struct vm_area_struct *vma, unsigned long vm_flags) > +{ > + /* > + * Shadow stack must be anonymous and not shared. > + */ > + if ((vm_flags & VM_SHADOW_STACK) && !vma_is_anonymous(vma)) > + return false; > + > + return true; > +} > + > +#define arch_validate_flags(vma, vm_flags) arch_validate_flags(vma, vm_flags) > + > +#endif /* CONFIG_X86_SHADOW_STACK */ > + > #endif /* _ASM_X86_MMAN_H */ > diff --git a/arch/x86/include/uapi/asm/mman.h b/arch/x86/include/uapi/asm/mman.h > index f28fa4acaeaf..4c36b263cf0a 100644 > --- a/arch/x86/include/uapi/asm/mman.h > +++ b/arch/x86/include/uapi/asm/mman.h > @@ -4,6 +4,8 @@ > > #define MAP_32BIT 0x40 /* only give out 32bit addresses */ > > +#define PROT_SHADOW_STACK 0x10 /* shadow stack pages */ > + > #include > > #endif /* _UAPI_ASM_X86_MMAN_H */ > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 1ccec5cc399b..9a7652eea207 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_SHADOW_STACK Nit: you can put VM_SHADOW_STACK directly into VM_FLAGS_CLEAR. It's already conditinal on the feature enabled and VM_NONE otherwise. Up to you. Reviewed-by: Kirill A. Shutemov -- Kirill A. Shutemov