From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754725AbdKJTcU (ORCPT ); Fri, 10 Nov 2017 14:32:20 -0500 Received: from mga04.intel.com ([192.55.52.120]:30435 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753687AbdKJTcP (ORCPT ); Fri, 10 Nov 2017 14:32:15 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.44,375,1505804400"; d="scan'208";a="6289281" Subject: [PATCH 27/30] x86, kaiser: un-poison PGDs at runtime To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, dave.hansen@linux.intel.com, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, hughd@google.com, x86@kernel.org From: Dave Hansen Date: Fri, 10 Nov 2017 11:31:57 -0800 References: <20171110193058.BECA7D88@viggo.jf.intel.com> In-Reply-To: <20171110193058.BECA7D88@viggo.jf.intel.com> Message-Id: <20171110193157.1B082BA6@viggo.jf.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen With KAISER Kernel PGDs that map userspace are "poisoned" with the NX bit. This ensures that if a kernel->user CR3 switch is missed, userspace crashes instead of running in an unhardened state. This code will be needed in a moment when KAISER is turned on and off at runtime. Note that an __ASSEMBLY__ #ifdef is now required since kaiser.h is indirectly included into assembly. Signed-off-by: Dave Hansen Cc: Moritz Lipp Cc: Daniel Gruss Cc: Michael Schwarz Cc: Richard Fellner Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Kees Cook Cc: Hugh Dickins Cc: x86@kernel.org --- b/arch/x86/include/asm/pgtable_64.h | 16 ++++++++++++++- b/arch/x86/mm/kaiser.c | 38 ++++++++++++++++++++++++++++++++++++ b/include/linux/kaiser.h | 3 +- 3 files changed, 55 insertions(+), 2 deletions(-) diff -puN arch/x86/include/asm/pgtable_64.h~kaiser-dynamic-unpoison-pgd arch/x86/include/asm/pgtable_64.h --- a/arch/x86/include/asm/pgtable_64.h~kaiser-dynamic-unpoison-pgd 2017-11-10 11:22:19.992244922 -0800 +++ b/arch/x86/include/asm/pgtable_64.h 2017-11-10 11:22:19.998244922 -0800 @@ -2,6 +2,7 @@ #define _ASM_X86_PGTABLE_64_H #include +#include #include #ifndef __ASSEMBLY__ @@ -196,6 +197,18 @@ static inline bool pgd_userspace_access( return (pgd.pgd & _PAGE_USER); } +static inline void kaiser_poison_pgd(pgd_t *pgd) +{ + if (pgd->pgd & _PAGE_PRESENT) + pgd->pgd |= _PAGE_NX; +} + +static inline void kaiser_unpoison_pgd(pgd_t *pgd) +{ + if (pgd->pgd & _PAGE_PRESENT) + pgd->pgd &= ~_PAGE_NX; +} + /* * Returns the pgd_t that the kernel should use in its page tables. */ @@ -216,7 +229,8 @@ static inline pgd_t kaiser_set_shadow_pg * wrong CR3 value, userspace will crash * instead of running. */ - pgd.pgd |= _PAGE_NX; + if (kaiser_active()) + kaiser_poison_pgd(&pgd); } } else if (!pgd.pgd) { /* diff -puN arch/x86/mm/kaiser.c~kaiser-dynamic-unpoison-pgd arch/x86/mm/kaiser.c --- a/arch/x86/mm/kaiser.c~kaiser-dynamic-unpoison-pgd 2017-11-10 11:22:19.993244922 -0800 +++ b/arch/x86/mm/kaiser.c 2017-11-10 11:22:19.999244922 -0800 @@ -488,6 +488,9 @@ static ssize_t kaiser_enabled_write_file if (enable > 1) return -EINVAL; + if (kaiser_enabled == enable) + return count; + WRITE_ONCE(kaiser_enabled, enable); return count; } @@ -505,3 +508,38 @@ static int __init create_kaiser_enabled( return 0; } late_initcall(create_kaiser_enabled); + +enum poison { + KAISER_POISON, + KAISER_UNPOISON +}; +void kaiser_poison_pgd_page(pgd_t *pgd_page, enum poison do_poison) +{ + int i = 0; + + for (i = 0; i < PTRS_PER_PGD; i++) { + pgd_t *pgd = &pgd_page[i]; + + /* Stop once we hit kernel addresses: */ + if (!pgdp_maps_userspace(pgd)) + break; + + if (do_poison == KAISER_POISON) + kaiser_poison_pgd(pgd); + else + kaiser_unpoison_pgd(pgd); + } + +} + +void kaiser_poison_pgds(enum poison do_poison) +{ + struct page *page; + + spin_lock(&pgd_lock); + list_for_each_entry(page, &pgd_list, lru) { + pgd_t *pgd = (pgd_t *)page_address(page); + kaiser_poison_pgd_page(pgd, do_poison); + } + spin_unlock(&pgd_lock); +} diff -puN include/linux/kaiser.h~kaiser-dynamic-unpoison-pgd include/linux/kaiser.h --- a/include/linux/kaiser.h~kaiser-dynamic-unpoison-pgd 2017-11-10 11:22:19.995244922 -0800 +++ b/include/linux/kaiser.h 2017-11-10 11:22:19.999244922 -0800 @@ -4,7 +4,7 @@ #ifdef CONFIG_KAISER #include #else - +#ifndef __ASSEMBLY__ /* * These stubs are used whenever CONFIG_KAISER is off, which * includes architectures that support KAISER, but have it @@ -29,5 +29,6 @@ static inline bool kaiser_active(void) { return 0; } +#endif /* __ASSEMBLY__ */ #endif /* !CONFIG_KAISER */ #endif /* _INCLUDE_KAISER_H */ _