Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752179AbdLAKoD (ORCPT ); Fri, 1 Dec 2017 05:44:03 -0500 Received: from mail-pl0-f68.google.com ([209.85.160.68]:45071 "EHLO mail-pl0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751918AbdLAKnf (ORCPT ); Fri, 1 Dec 2017 05:43:35 -0500 X-Google-Smtp-Source: AGs4zMbiE9tO06cVtn7uYL8RSML9iy8qzNv2w8HRw6v/RaA2s21sGl0IjwNCz3S17wD0XWhC2XAJ8g== From: "jinb.park" X-Google-Original-From: "jinb.park" Date: Fri, 1 Dec 2017 19:43:28 +0900 To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Cc: afzal.mohd.ma@gmail.com, mark.rutland@arm.com, labbott@redhat.com, linux@armlinux.org.uk, gregkh@linuxfoundation.org, keescook@chromium.org, vladimir.murzin@arm.com, arnd@arndb.de Subject: [kernel-hardening][PATCH 3/3] arm: mm: dump: add checking for writable and executable pages Message-ID: <20171201104328.GA4014@pjb1027-Latitude-E5410> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5789 Lines: 212 Page mappings with full RWX permissions are a security risk. x86, arm64 has an option to walk the page tables and dump any bad pages. (1404d6f13e47 ("arm64: dump: Add checking for writable and exectuable pages")) Add a similar implementation for arm. Signed-off-by: Jinbum Park --- arch/arm/Kconfig.debug | 27 +++++++++++++++ arch/arm/include/asm/ptdump.h | 8 +++++ arch/arm/mm/dump.c | 78 +++++++++++++++++++++++++++++++++++++++++++ arch/arm/mm/init.c | 2 ++ 4 files changed, 115 insertions(+) diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index e7b94db..78a6470 100644 --- a/arch/arm/Kconfig.debug +++ b/arch/arm/Kconfig.debug @@ -20,6 +20,33 @@ config ARM_PTDUMP_DEBUGFS kernel. If in doubt, say "N" +config DEBUG_WX + bool "Warn on W+X mappings at boot" + select ARM_PTDUMP_CORE + ---help--- + Generate a warning if any W+X mappings are found at boot. + + This is useful for discovering cases where the kernel is leaving + W+X mappings after applying NX, as such mappings are a security risk. + + Look for a message in dmesg output like this: + + arm/mm: Checked W+X mappings: passed, no W+X pages found. + + or like this, if the check failed: + + arm/mm: Checked W+X mappings: FAILED, W+X pages found. + + Note that even if the check fails, your kernel is possibly + still fine, as W+X mappings are not a security hole in + themselves, what they do is that they make the exploitation + of other unfixed kernel bugs easier. + + There is no runtime or memory usage effect of this option + once the kernel has booted up - it's a one time check. + + If in doubt, say "Y". + # RMK wants arm kernels compiled with frame pointers or stack unwinding. # If you know what you are doing and are willing to live without stack # traces, you can get a slightly smaller kernel by setting this option to diff --git a/arch/arm/include/asm/ptdump.h b/arch/arm/include/asm/ptdump.h index 3a6c0b7..b6a0162 100644 --- a/arch/arm/include/asm/ptdump.h +++ b/arch/arm/include/asm/ptdump.h @@ -43,6 +43,14 @@ static inline int ptdump_debugfs_register(struct ptdump_info *info, } #endif /* CONFIG_ARM_PTDUMP_DEBUGFS */ +void ptdump_check_wx(void); + #endif /* CONFIG_ARM_PTDUMP_CORE */ +#ifdef CONFIG_DEBUG_WX +#define debug_checkwx() ptdump_check_wx() +#else +#define debug_checkwx() do { } while (0) +#endif + #endif /* __ASM_PTDUMP_H */ diff --git a/arch/arm/mm/dump.c b/arch/arm/mm/dump.c index 43a2bee..a0a4b30 100644 --- a/arch/arm/mm/dump.c +++ b/arch/arm/mm/dump.c @@ -52,6 +52,8 @@ struct pg_state { unsigned long start_address; unsigned level; u64 current_prot; + bool check_wx; + unsigned long wx_pages; const char *current_domain; }; @@ -226,6 +228,60 @@ static void dump_prot(struct pg_state *st, const struct prot_bits *bits, size_t } } +static inline bool is_prot_ro(struct pg_state *st) +{ + if (st->level < 4) { + #ifdef CONFIG_ARM_LPAE + if ((st->current_prot & + (L_PMD_SECT_RDONLY | PMD_SECT_AP2)) == + (L_PMD_SECT_RDONLY | PMD_SECT_AP2)) + return true; + #elif __LINUX_ARM_ARCH__ >= 6 + if ((st->current_prot & + (PMD_SECT_APX | PMD_SECT_AP_READ | PMD_SECT_AP_WRITE)) == + (PMD_SECT_APX | PMD_SECT_AP_WRITE)) + return true; + #else + if ((st->current_prot & + (PMD_SECT_AP_READ | PMD_SECT_AP_WRITE)) == 0) + return true; + #endif + } else { + if ((st->current_prot & L_PTE_RDONLY) == L_PTE_RDONLY) + return true; + } + + return false; +} + +static inline bool is_prot_nx(struct pg_state *st) +{ + if (st->level < 4) { + if ((st->current_prot & PMD_SECT_XN) == PMD_SECT_XN) + return true; + } else { + if ((st->current_prot & L_PTE_XN) == L_PTE_XN) + return true; + } + + return false; +} + +static void note_prot_wx(struct pg_state *st, unsigned long addr) +{ + if (!st->check_wx) + return; + if (is_prot_ro(st)) + return; + if (is_prot_nx(st)) + return; + + WARN_ONCE(1, "arm/mm: Found insecure W+X mapping at address %p/%pS\n", + (void *)st->start_address, (void *)st->start_address); + + st->wx_pages += (addr - st->start_address) / PAGE_SIZE; +} + static void note_page(struct pg_state *st, unsigned long addr, unsigned int level, u64 val, const char *domain) { @@ -244,6 +300,7 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned long delta; if (st->current_prot) { + note_prot_wx(st, addr); pt_dump_seq_printf(st->seq, "0x%08lx-0x%08lx ", st->start_address, addr); @@ -367,6 +424,7 @@ void ptdump_walk_pgd(struct seq_file *m, struct ptdump_info *info) struct pg_state st = { .seq = m, .marker = info->markers, + .check_wx = false, }; walk_pgd(&st, info->mm, info->base_addr); @@ -391,6 +449,26 @@ static void ptdump_initialize(void) .base_addr = 0, }; +void ptdump_check_wx(void) +{ + struct pg_state st = { + .seq = NULL, + .marker = (struct addr_marker[]) { + { 0, NULL}, + { -1, NULL}, + }, + .check_wx = true, + }; + + walk_pgd(&st, &init_mm, 0); + note_page(&st, 0, 0, 0, NULL); + if (st.wx_pages) + pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found\n", + st.wx_pages); + else + pr_info("Checked W+X mappings: passed, no W+X pages found\n"); +} + static int ptdump_init(void) { ptdump_initialize(); diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index a1f11a7..bd6f451 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include @@ -738,6 +739,7 @@ static int __mark_rodata_ro(void *unused) void mark_rodata_ro(void) { stop_machine(__mark_rodata_ro, NULL, NULL); + debug_checkwx(); } void set_kernel_text_rw(void) -- 1.9.1