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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7315CC35270 for ; Sun, 30 Jan 2022 21:22:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id ECC0B6B0088; Sun, 30 Jan 2022 16:21:55 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E00726B0087; Sun, 30 Jan 2022 16:21:55 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C2C676B0085; Sun, 30 Jan 2022 16:21:55 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0008.hostedemail.com [216.40.44.8]) by kanga.kvack.org (Postfix) with ESMTP id 9F5736B0082 for ; Sun, 30 Jan 2022 16:21:55 -0500 (EST) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 5F28291ACD for ; Sun, 30 Jan 2022 21:21:55 +0000 (UTC) X-FDA: 79088225790.06.6D3C0AF Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by imf18.hostedemail.com (Postfix) with ESMTP id A65DA1C0005 for ; Sun, 30 Jan 2022 21:21:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1643577714; x=1675113714; h=from:to:cc:subject:date:message-id:in-reply-to: references; bh=xkVnTjzi6+uetv9e83D2AA4YYyIEZnM0yn9xpSFsd90=; b=Vr8QKKH+tiVI1lXdP33MnyXdVLQk8hU7hSrFXd5PH9QBmH1iToZbWdme Q9mzDgxTMvOjI0YNdq5GxGVvYX5iiIgisqWxgZSraTm/hkkkfa55dIQhz kMrogrGDcjpaoXwW7vPYcCGGDLm+OLyRWog60p/Ijkp7BZKnwqRTsatKj GuhzabKSN+kit0UYzjUo4NAYOOG5syYCN/HEEjDB7H23Q9w13IwahYcU3 03zriwR01zWAalKqqN8848Wqxu9KFy3NFTqU+1MrA/0R8yupZ4ZQ7kpgN 335dEwIBkX8F3ksyfx4YQMeNlhkv6Id8e5xaImjU1TyI6e/3pMM1JGOYE A==; X-IronPort-AV: E=McAfee;i="6200,9189,10243"; a="244970193" X-IronPort-AV: E=Sophos;i="5.88,329,1635231600"; d="scan'208";a="244970193" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Jan 2022 13:21:53 -0800 X-IronPort-AV: E=Sophos;i="5.88,329,1635231600"; d="scan'208";a="536856732" Received: from avmallar-mobl1.amr.corp.intel.com (HELO rpedgeco-desk.amr.corp.intel.com) ([10.209.123.171]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Jan 2022 13:21:52 -0800 From: Rick Edgecombe 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" , Dave Martin , Weijiang Yang , "Kirill A . Shutemov" , joao.moreira@intel.com, John Allen , kcc@google.com, eranian@google.com Cc: rick.p.edgecombe@intel.com, Yu-cheng Yu Subject: [PATCH 09/35] x86/mm: Introduce _PAGE_COW Date: Sun, 30 Jan 2022 13:18:12 -0800 Message-Id: <20220130211838.8382-10-rick.p.edgecombe@intel.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20220130211838.8382-1-rick.p.edgecombe@intel.com> References: <20220130211838.8382-1-rick.p.edgecombe@intel.com> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: A65DA1C0005 X-Stat-Signature: dtr7fdqyobjnd4ijqkzfdywiuby6dwcp X-Rspam-User: nil Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=Vr8QKKH+; spf=none (imf18.hostedemail.com: domain of rick.p.edgecombe@intel.com has no SPF policy when checking 192.55.52.93) smtp.mailfrom=rick.p.edgecombe@intel.com; dmarc=pass (policy=none) header.from=intel.com X-HE-Tag: 1643577714-461434 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Yu-cheng Yu There is essentially no room left in the x86 hardware PTEs on some OSes (not Linux). That left the hardware architects looking for a way to represent a new memory type (shadow stack) within the existing bits. They chose to repurpose a lightly-used state: Write=0, Dirty=1. The reason it's lightly used is that Dirty=1 is normally set by hardware and cannot normally be set by hardware on a Write=0 PTE. Software must normally be involved to create one of these PTEs, so software can simply opt to not create them. In places where Linux normally creates Write=0, Dirty=1, it can use the software-defined _PAGE_COW in place of the hardware _PAGE_DIRTY. In other words, whenever Linux needs to create Write=0, Dirty=1, it instead creates Write=0, Cow=1, except for shadow stack, which is Write=0, Dirty=1. This clearly separates shadow stack from other data, and results in the following: (a) A modified, copy-on-write (COW) page: (Write=0, Cow=1) (b) A R/O page that has been COW'ed: (Write=0, Cow=1) The user page is in a R/O VMA, and get_user_pages() needs a writable copy. The page fault handler creates a copy of the page and sets the new copy's PTE as Write=0 and Cow=1. (c) A shadow stack PTE: (Write=0, Dirty=1) (d) A shared shadow stack PTE: (Write=0, Cow=1) When a shadow stack page is being shared among processes (this happens at fork()), its PTE is made Dirty=0, so the next shadow stack access causes a fault, and the page is duplicated and Dirty=1 is set again. This is the COW equivalent for shadow stack pages, even though it's copy-on-access rather than copy-on-write. (e) A page where the processor observed a Write=1 PTE, started a write, set Dirty=1, but then observed a Write=0 PTE. That's possible today, but will not happen on processors that support shadow stack. Define _PAGE_COW and update pte_*() helpers and apply the same changes to pmd and pud. After this, there are six free bits left in the 64-bit PTE, and no more free bits in the 32-bit PTE (except for PAE) and Shadow Stack is not implemented for the 32-bit kernel. Signed-off-by: Yu-cheng Yu Reviewed-by: Kirill A. Shutemov Signed-off-by: Rick Edgecombe --- arch/x86/include/asm/pgtable.h | 196 ++++++++++++++++++++++++--- arch/x86/include/asm/pgtable_types.h | 42 +++++- 2 files changed, 217 insertions(+), 21 deletions(-) diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index aff5e489ff17..a4a75e78a934 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -123,9 +123,20 @@ extern pmdval_t early_pmd_flags; * The following only work if pte_present() is true. * Undefined behaviour if not.. */ -static inline int pte_dirty(pte_t pte) +static inline bool pte_dirty(pte_t pte) { - return pte_flags(pte) & _PAGE_DIRTY; + /* + * A dirty PTE has Dirty=1 or Cow=1. + */ + return pte_flags(pte) & _PAGE_DIRTY_BITS; +} + +static inline bool pte_shstk(pte_t pte) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return false; + + return (pte_flags(pte) & (_PAGE_RW | _PAGE_DIRTY)) == _PAGE_DIRTY; } static inline int pte_young(pte_t pte) @@ -133,9 +144,20 @@ static inline int pte_young(pte_t pte) return pte_flags(pte) & _PAGE_ACCESSED; } -static inline int pmd_dirty(pmd_t pmd) +static inline bool pmd_dirty(pmd_t pmd) { - return pmd_flags(pmd) & _PAGE_DIRTY; + /* + * A dirty PMD has Dirty=1 or Cow=1. + */ + return pmd_flags(pmd) & _PAGE_DIRTY_BITS; +} + +static inline bool pmd_shstk(pmd_t pmd) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return false; + + return (pmd_flags(pmd) & (_PAGE_RW | _PAGE_DIRTY)) == _PAGE_DIRTY; } static inline int pmd_young(pmd_t pmd) @@ -143,9 +165,12 @@ static inline int pmd_young(pmd_t pmd) return pmd_flags(pmd) & _PAGE_ACCESSED; } -static inline int pud_dirty(pud_t pud) +static inline bool pud_dirty(pud_t pud) { - return pud_flags(pud) & _PAGE_DIRTY; + /* + * A dirty PUD has Dirty=1 or Cow=1. + */ + return pud_flags(pud) & _PAGE_DIRTY_BITS; } static inline int pud_young(pud_t pud) @@ -155,13 +180,23 @@ static inline int pud_young(pud_t pud) static inline int pte_write(pte_t pte) { - return pte_flags(pte) & _PAGE_RW; + /* + * Shadow stack pages are always writable - but not by normal + * instructions, and only by shadow stack operations. Therefore, + * the W=0,D=1 test with pte_shstk(). + */ + return (pte_flags(pte) & _PAGE_RW) || pte_shstk(pte); } #define pmd_write pmd_write static inline int pmd_write(pmd_t pmd) { - return pmd_flags(pmd) & _PAGE_RW; + /* + * Shadow stack pages are always writable - but not by normal + * instructions, and only by shadow stack operations. Therefore, + * the W=0,D=1 test with pmd_shstk(). + */ + return (pmd_flags(pmd) & _PAGE_RW) || pmd_shstk(pmd); } #define pud_write pud_write @@ -299,6 +334,24 @@ static inline pte_t pte_clear_flags(pte_t pte, pteval_t clear) return native_make_pte(v & ~clear); } +static inline pte_t pte_mkcow(pte_t pte) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return pte; + + pte = pte_clear_flags(pte, _PAGE_DIRTY); + return pte_set_flags(pte, _PAGE_COW); +} + +static inline pte_t pte_clear_cow(pte_t pte) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return pte; + + pte = pte_set_flags(pte, _PAGE_DIRTY); + return pte_clear_flags(pte, _PAGE_COW); +} + #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP static inline int pte_uffd_wp(pte_t pte) { @@ -318,7 +371,7 @@ static inline pte_t pte_clear_uffd_wp(pte_t pte) static inline pte_t pte_mkclean(pte_t pte) { - return pte_clear_flags(pte, _PAGE_DIRTY); + return pte_clear_flags(pte, _PAGE_DIRTY_BITS); } static inline pte_t pte_mkold(pte_t pte) @@ -328,7 +381,16 @@ static inline pte_t pte_mkold(pte_t pte) static inline pte_t pte_wrprotect(pte_t pte) { - return pte_clear_flags(pte, _PAGE_RW); + pte = pte_clear_flags(pte, _PAGE_RW); + + /* + * Blindly clearing _PAGE_RW might accidentally create + * a shadow stack PTE (RW=0, Dirty=1). Move the hardware + * dirty value to the software bit. + */ + if (pte_dirty(pte)) + pte = pte_mkcow(pte); + return pte; } static inline pte_t pte_mkexec(pte_t pte) @@ -338,7 +400,18 @@ static inline pte_t pte_mkexec(pte_t pte) static inline pte_t pte_mkdirty(pte_t pte) { - return pte_set_flags(pte, _PAGE_DIRTY | _PAGE_SOFT_DIRTY); + pteval_t dirty = _PAGE_DIRTY; + + /* Avoid creating (HW)Dirty=1, Write=0 PTEs */ + if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pte_write(pte)) + dirty = _PAGE_COW; + + return pte_set_flags(pte, dirty | _PAGE_SOFT_DIRTY); +} + +static inline pte_t pte_mkwrite_shstk(pte_t pte) +{ + return pte_clear_cow(pte); } static inline pte_t pte_mkyoung(pte_t pte) @@ -348,7 +421,12 @@ static inline pte_t pte_mkyoung(pte_t pte) static inline pte_t pte_mkwrite(pte_t pte) { - return pte_set_flags(pte, _PAGE_RW); + pte = pte_set_flags(pte, _PAGE_RW); + + if (pte_dirty(pte)) + pte = pte_clear_cow(pte); + + return pte; } static inline pte_t pte_mkhuge(pte_t pte) @@ -395,6 +473,24 @@ static inline pmd_t pmd_clear_flags(pmd_t pmd, pmdval_t clear) return native_make_pmd(v & ~clear); } +static inline pmd_t pmd_mkcow(pmd_t pmd) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return pmd; + + pmd = pmd_clear_flags(pmd, _PAGE_DIRTY); + return pmd_set_flags(pmd, _PAGE_COW); +} + +static inline pmd_t pmd_clear_cow(pmd_t pmd) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return pmd; + + pmd = pmd_set_flags(pmd, _PAGE_DIRTY); + return pmd_clear_flags(pmd, _PAGE_COW); +} + #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP static inline int pmd_uffd_wp(pmd_t pmd) { @@ -419,17 +515,36 @@ static inline pmd_t pmd_mkold(pmd_t pmd) static inline pmd_t pmd_mkclean(pmd_t pmd) { - return pmd_clear_flags(pmd, _PAGE_DIRTY); + return pmd_clear_flags(pmd, _PAGE_DIRTY_BITS); } static inline pmd_t pmd_wrprotect(pmd_t pmd) { - return pmd_clear_flags(pmd, _PAGE_RW); + pmd = pmd_clear_flags(pmd, _PAGE_RW); + /* + * Blindly clearing _PAGE_RW might accidentally create + * a shadow stack PMD (RW=0, Dirty=1). Move the hardware + * dirty value to the software bit. + */ + if (pmd_dirty(pmd)) + pmd = pmd_mkcow(pmd); + return pmd; } static inline pmd_t pmd_mkdirty(pmd_t pmd) { - return pmd_set_flags(pmd, _PAGE_DIRTY | _PAGE_SOFT_DIRTY); + pmdval_t dirty = _PAGE_DIRTY; + + /* Avoid creating (HW)Dirty=1, Write=0 PMDs */ + if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pmd_write(pmd)) + dirty = _PAGE_COW; + + return pmd_set_flags(pmd, dirty | _PAGE_SOFT_DIRTY); +} + +static inline pmd_t pmd_mkwrite_shstk(pmd_t pmd) +{ + return pmd_clear_cow(pmd); } static inline pmd_t pmd_mkdevmap(pmd_t pmd) @@ -449,7 +564,11 @@ static inline pmd_t pmd_mkyoung(pmd_t pmd) static inline pmd_t pmd_mkwrite(pmd_t pmd) { - return pmd_set_flags(pmd, _PAGE_RW); + pmd = pmd_set_flags(pmd, _PAGE_RW); + + if (pmd_dirty(pmd)) + pmd = pmd_clear_cow(pmd); + return pmd; } static inline pud_t pud_set_flags(pud_t pud, pudval_t set) @@ -466,6 +585,24 @@ static inline pud_t pud_clear_flags(pud_t pud, pudval_t clear) return native_make_pud(v & ~clear); } +static inline pud_t pud_mkcow(pud_t pud) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return pud; + + pud = pud_clear_flags(pud, _PAGE_DIRTY); + return pud_set_flags(pud, _PAGE_COW); +} + +static inline pud_t pud_clear_cow(pud_t pud) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return pud; + + pud = pud_set_flags(pud, _PAGE_DIRTY); + return pud_clear_flags(pud, _PAGE_COW); +} + static inline pud_t pud_mkold(pud_t pud) { return pud_clear_flags(pud, _PAGE_ACCESSED); @@ -473,17 +610,32 @@ static inline pud_t pud_mkold(pud_t pud) static inline pud_t pud_mkclean(pud_t pud) { - return pud_clear_flags(pud, _PAGE_DIRTY); + return pud_clear_flags(pud, _PAGE_DIRTY_BITS); } static inline pud_t pud_wrprotect(pud_t pud) { - return pud_clear_flags(pud, _PAGE_RW); + pud = pud_clear_flags(pud, _PAGE_RW); + + /* + * Blindly clearing _PAGE_RW might accidentally create + * a shadow stack PUD (RW=0, Dirty=1). Move the hardware + * dirty value to the software bit. + */ + if (pud_dirty(pud)) + pud = pud_mkcow(pud); + return pud; } static inline pud_t pud_mkdirty(pud_t pud) { - return pud_set_flags(pud, _PAGE_DIRTY | _PAGE_SOFT_DIRTY); + pudval_t dirty = _PAGE_DIRTY; + + /* Avoid creating (HW)Dirty=1, Write=0 PUDs */ + if (cpu_feature_enabled(X86_FEATURE_SHSTK) && !pud_write(pud)) + dirty = _PAGE_COW; + + return pud_set_flags(pud, dirty | _PAGE_SOFT_DIRTY); } static inline pud_t pud_mkdevmap(pud_t pud) @@ -503,7 +655,11 @@ static inline pud_t pud_mkyoung(pud_t pud) static inline pud_t pud_mkwrite(pud_t pud) { - return pud_set_flags(pud, _PAGE_RW); + pud = pud_set_flags(pud, _PAGE_RW); + + if (pud_dirty(pud)) + pud = pud_clear_cow(pud); + return pud; } #ifdef CONFIG_HAVE_ARCH_SOFT_DIRTY diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h index 3781a79b6388..1bfab70ff9ac 100644 --- a/arch/x86/include/asm/pgtable_types.h +++ b/arch/x86/include/asm/pgtable_types.h @@ -21,7 +21,8 @@ #define _PAGE_BIT_SOFTW2 10 /* " */ #define _PAGE_BIT_SOFTW3 11 /* " */ #define _PAGE_BIT_PAT_LARGE 12 /* On 2MB or 1GB pages */ -#define _PAGE_BIT_SOFTW4 58 /* available for programmer */ +#define _PAGE_BIT_SOFTW4 57 /* available for programmer */ +#define _PAGE_BIT_SOFTW5 58 /* available for programmer */ #define _PAGE_BIT_PKEY_BIT0 59 /* Protection Keys, bit 1/4 */ #define _PAGE_BIT_PKEY_BIT1 60 /* Protection Keys, bit 2/4 */ #define _PAGE_BIT_PKEY_BIT2 61 /* Protection Keys, bit 3/4 */ @@ -34,6 +35,15 @@ #define _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty tracking */ #define _PAGE_BIT_DEVMAP _PAGE_BIT_SOFTW4 +/* + * Indicates a copy-on-write page. + */ +#ifdef CONFIG_X86_SHADOW_STACK +#define _PAGE_BIT_COW _PAGE_BIT_SOFTW5 /* copy-on-write */ +#else +#define _PAGE_BIT_COW 0 +#endif + /* If _PAGE_BIT_PRESENT is clear, we use these: */ /* - if the user mapped it with PROT_NONE; pte_present gives true */ #define _PAGE_BIT_PROTNONE _PAGE_BIT_GLOBAL @@ -115,6 +125,36 @@ #define _PAGE_DEVMAP (_AT(pteval_t, 0)) #endif +/* + * The hardware requires shadow stack to be read-only and Dirty. + * _PAGE_COW is a software-only bit used to separate copy-on-write PTEs + * from shadow stack PTEs: + * (a) A modified, copy-on-write (COW) page: (Write=0, Cow=1) + * (b) A R/O page that has been COW'ed: (Write=0, Cow=1) + * The user page is in a R/O VMA, and get_user_pages() needs a + * writable copy. The page fault handler creates a copy of the page + * and sets the new copy's PTE as Write=0, Cow=1. + * (c) A shadow stack PTE: (Write=0, Dirty=1) + * (d) A shared (copy-on-access) shadow stack PTE: (Write=0, Cow=1) + * When a shadow stack page is being shared among processes (this + * happens at fork()), its PTE is cleared of _PAGE_DIRTY, so the next + * shadow stack access causes a fault, and the page is duplicated and + * _PAGE_DIRTY is set again. This is the COW equivalent for shadow + * stack pages, even though it's copy-on-access rather than + * copy-on-write. + * (e) A page where the processor observed a Write=1 PTE, started a write, + * set Dirty=1, but then observed a Write=0 PTE (changed by another + * thread). That's possible today, but will not happen on processors + * that support shadow stack. + */ +#ifdef CONFIG_X86_SHADOW_STACK +#define _PAGE_COW (_AT(pteval_t, 1) << _PAGE_BIT_COW) +#else +#define _PAGE_COW (_AT(pteval_t, 0)) +#endif + +#define _PAGE_DIRTY_BITS (_PAGE_DIRTY | _PAGE_COW) + #define _PAGE_PROTNONE (_AT(pteval_t, 1) << _PAGE_BIT_PROTNONE) /* -- 2.17.1