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Message-Id: <20181023213504.28905-2-igor.stoppa@huawei.com>
Date: Wed, 24 Oct 2018 00:34:48 +0300
From: Igor Stoppa <igor.stoppa@...il.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Kees Cook <keescook@...omium.org>,
Matthew Wilcox <willy@...radead.org>,
Dave Chinner <david@...morbit.com>,
James Morris <jmorris@...ei.org>,
Michal Hocko <mhocko@...nel.org>,
kernel-hardening@...ts.openwall.com,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org
Cc: igor.stoppa@...wei.com,
Dave Hansen <dave.hansen@...ux.intel.com>,
Jonathan Corbet <corbet@....net>,
Laura Abbott <labbott@...hat.com>,
Arnd Bergmann <arnd@...db.de>,
Thomas Gleixner <tglx@...utronix.de>,
Kate Stewart <kstewart@...uxfoundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Philippe Ombredanne <pombredanne@...b.com>,
linux-arch@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH 01/17] prmem: linker section for static write rare
Introduce a section and a label for statically allocated write rare
data.
The label is named "__write_rare_after_init".
As the name implies, after the init phase is completed, this section
will be modifiable only by invoking write rare functions.
NOTE:
this needs rework, because the current write-rare mechanism works
only on x86_64 and not arm64, due to arm64 mappings.
Signed-off-by: Igor Stoppa <igor.stoppa@...wei.com>
CC: Arnd Bergmann <arnd@...db.de>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Kate Stewart <kstewart@...uxfoundation.org>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Philippe Ombredanne <pombredanne@...b.com>
CC: linux-arch@...r.kernel.org
CC: linux-kernel@...r.kernel.org
---
include/asm-generic/vmlinux.lds.h | 20 ++++++++++++++++++++
include/linux/cache.h | 17 +++++++++++++++++
2 files changed, 37 insertions(+)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index d7701d466b60..fd40a15e3b24 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -300,6 +300,25 @@
. = __start_init_task + THREAD_SIZE; \
__end_init_task = .;
+/*
+ * Allow architectures to handle wr_after_init data on their
+ * own by defining an empty WR_AFTER_INIT_DATA.
+ * However, it's important that pages containing WR_RARE data do not
+ * hold anything else, to avoid both accidentally unprotecting something
+ * that is supposed to stay read-only all the time and also to protect
+ * something else that is supposed to be writeable all the time.
+ */
+#ifndef WR_AFTER_INIT_DATA
+#define WR_AFTER_INIT_DATA(align) \
+ . = ALIGN(PAGE_SIZE); \
+ __start_wr_after_init = .; \
+ . = ALIGN(align); \
+ *(.data..wr_after_init) \
+ . = ALIGN(PAGE_SIZE); \
+ __end_wr_after_init = .; \
+ . = ALIGN(align);
+#endif
+
/*
* Allow architectures to handle ro_after_init data on their
* own by defining an empty RO_AFTER_INIT_DATA.
@@ -320,6 +339,7 @@
__start_rodata = .; \
*(.rodata) *(.rodata.*) \
RO_AFTER_INIT_DATA /* Read only after init */ \
+ WR_AFTER_INIT_DATA(align) /* wr after init */ \
KEEP(*(__vermagic)) /* Kernel version magic */ \
. = ALIGN(8); \
__start___tracepoints_ptrs = .; \
diff --git a/include/linux/cache.h b/include/linux/cache.h
index 750621e41d1c..9a7e7134b887 100644
--- a/include/linux/cache.h
+++ b/include/linux/cache.h
@@ -31,6 +31,23 @@
#define __ro_after_init __attribute__((__section__(".data..ro_after_init")))
#endif
+/*
+ * __wr_after_init is used to mark objects that cannot be modified
+ * directly after init (i.e. after mark_rodata_ro() has been called).
+ * These objects become effectively read-only, from the perspective of
+ * performing a direct write, like a variable assignment.
+ * However, they can be altered through a dedicated function.
+ * It is intended for those objects which are occasionally modified after
+ * init, however they are modified so seldomly, that the extra cost from
+ * the indirect modification is either negligible or worth paying, for the
+ * sake of the protection gained.
+ */
+#ifndef __wr_after_init
+#define __wr_after_init \
+ __attribute__((__section__(".data..wr_after_init")))
+#endif
+
+
#ifndef ____cacheline_aligned
#define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES)))
#endif
--
2.17.1
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