From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kees Cook Subject: [PATCH v5 4/7] introduce post-init read-only memory Date: Wed, 17 Feb 2016 14:41:15 -0800 Message-ID: <1455748879-21872-5-git-send-email-keescook@chromium.org> References: <1455748879-21872-1-git-send-email-keescook@chromium.org> Return-path: In-Reply-To: <1455748879-21872-1-git-send-email-keescook@chromium.org> Sender: linux-kernel-owner@vger.kernel.org To: Ingo Molnar Cc: Kees Cook , David Brown , Andy Lutomirski , "H. Peter Anvin" , Michael Ellerman , Mathias Krause , Thomas Gleixner , x86@kernel.org, Arnd Bergmann , PaX Team , Emese Revfy , kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, linux-arch List-Id: linux-arch.vger.kernel.org One of the easiest ways to protect the kernel from attack is to reduce the internal attack surface exposed when a "write" flaw is available. By making as much of the kernel read-only as possible, we reduce the attack surface. Many things are written to only during __init, and never changed again. These cannot be made "const" since the compiler will do the wrong thing (we do actually need to write to them). Instead, move these items into a memory region that will be made read-only during mark_rodata_ro() which happens after all kernel __init code has finished. This introduces __ro_after_init as a way to mark such memory, and adds some documentation about the existing __read_mostly marking. Based on work by PaX Team and Brad Spengler. Signed-off-by: Kees Cook --- arch/parisc/include/asm/cache.h | 3 +++ include/asm-generic/vmlinux.lds.h | 1 + include/linux/cache.h | 14 ++++++++++++++ 3 files changed, 18 insertions(+) diff --git a/arch/parisc/include/asm/cache.h b/arch/parisc/include/asm/cache.h index 3d0e17bcc8e9..df0f52bd18b4 100644 --- a/arch/parisc/include/asm/cache.h +++ b/arch/parisc/include/asm/cache.h @@ -22,6 +22,9 @@ #define __read_mostly __attribute__((__section__(".data..read_mostly"))) +/* Read-only memory is marked before mark_rodata_ro() is called. */ +#define __ro_after_init __read_mostly + void parisc_cache_init(void); /* initializes cache-flushing */ void disable_sr_hashing_asm(int); /* low level support for above */ void disable_sr_hashing(void); /* turns off space register hashing */ diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index e9a81a6a109f..8f5a12ab2f2b 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -255,6 +255,7 @@ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start_rodata) = .; \ *(.rodata) *(.rodata.*) \ + *(.data..ro_after_init) /* Read only after init */ \ *(__vermagic) /* Kernel version magic */ \ . = ALIGN(8); \ VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \ diff --git a/include/linux/cache.h b/include/linux/cache.h index 17e7e82d2aa7..1be04f8c563a 100644 --- a/include/linux/cache.h +++ b/include/linux/cache.h @@ -12,10 +12,24 @@ #define SMP_CACHE_BYTES L1_CACHE_BYTES #endif +/* + * __read_mostly is used to keep rarely changing variables out of frequently + * updated cachelines. If an architecture doesn't support it, ignore the + * hint. + */ #ifndef __read_mostly #define __read_mostly #endif +/* + * __ro_after_init is used to mark things that are read-only after init (i.e. + * after mark_rodata_ro() has been called). These are effectively read-only, + * but may get written to during init, so can't live in .rodata (via "const"). + */ +#ifndef __ro_after_init +#define __ro_after_init __attribute__((__section__(".data..ro_after_init"))) +#endif + #ifndef ____cacheline_aligned #define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES))) #endif -- 2.6.3 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f52.google.com ([209.85.220.52]:33817 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1424243AbcBQWly (ORCPT ); Wed, 17 Feb 2016 17:41:54 -0500 Received: by mail-pa0-f52.google.com with SMTP id fy10so18666271pac.1 for ; Wed, 17 Feb 2016 14:41:53 -0800 (PST) From: Kees Cook Subject: [PATCH v5 4/7] introduce post-init read-only memory Date: Wed, 17 Feb 2016 14:41:15 -0800 Message-ID: <1455748879-21872-5-git-send-email-keescook@chromium.org> In-Reply-To: <1455748879-21872-1-git-send-email-keescook@chromium.org> References: <1455748879-21872-1-git-send-email-keescook@chromium.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Ingo Molnar Cc: Kees Cook , David Brown , Andy Lutomirski , "H. Peter Anvin" , Michael Ellerman , Mathias Krause , Thomas Gleixner , x86@kernel.org, Arnd Bergmann , PaX Team , Emese Revfy , kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, linux-arch Message-ID: <20160217224115.OPxTjEXLsrJIs-oXRcy3QlvTUc8S_92sX8rMqK3Mafg@z> One of the easiest ways to protect the kernel from attack is to reduce the internal attack surface exposed when a "write" flaw is available. By making as much of the kernel read-only as possible, we reduce the attack surface. Many things are written to only during __init, and never changed again. These cannot be made "const" since the compiler will do the wrong thing (we do actually need to write to them). Instead, move these items into a memory region that will be made read-only during mark_rodata_ro() which happens after all kernel __init code has finished. This introduces __ro_after_init as a way to mark such memory, and adds some documentation about the existing __read_mostly marking. Based on work by PaX Team and Brad Spengler. Signed-off-by: Kees Cook --- arch/parisc/include/asm/cache.h | 3 +++ include/asm-generic/vmlinux.lds.h | 1 + include/linux/cache.h | 14 ++++++++++++++ 3 files changed, 18 insertions(+) diff --git a/arch/parisc/include/asm/cache.h b/arch/parisc/include/asm/cache.h index 3d0e17bcc8e9..df0f52bd18b4 100644 --- a/arch/parisc/include/asm/cache.h +++ b/arch/parisc/include/asm/cache.h @@ -22,6 +22,9 @@ #define __read_mostly __attribute__((__section__(".data..read_mostly"))) +/* Read-only memory is marked before mark_rodata_ro() is called. */ +#define __ro_after_init __read_mostly + void parisc_cache_init(void); /* initializes cache-flushing */ void disable_sr_hashing_asm(int); /* low level support for above */ void disable_sr_hashing(void); /* turns off space register hashing */ diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index e9a81a6a109f..8f5a12ab2f2b 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -255,6 +255,7 @@ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start_rodata) = .; \ *(.rodata) *(.rodata.*) \ + *(.data..ro_after_init) /* Read only after init */ \ *(__vermagic) /* Kernel version magic */ \ . = ALIGN(8); \ VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \ diff --git a/include/linux/cache.h b/include/linux/cache.h index 17e7e82d2aa7..1be04f8c563a 100644 --- a/include/linux/cache.h +++ b/include/linux/cache.h @@ -12,10 +12,24 @@ #define SMP_CACHE_BYTES L1_CACHE_BYTES #endif +/* + * __read_mostly is used to keep rarely changing variables out of frequently + * updated cachelines. If an architecture doesn't support it, ignore the + * hint. + */ #ifndef __read_mostly #define __read_mostly #endif +/* + * __ro_after_init is used to mark things that are read-only after init (i.e. + * after mark_rodata_ro() has been called). These are effectively read-only, + * but may get written to during init, so can't live in .rodata (via "const"). + */ +#ifndef __ro_after_init +#define __ro_after_init __attribute__((__section__(".data..ro_after_init"))) +#endif + #ifndef ____cacheline_aligned #define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES))) #endif -- 2.6.3