From 25362dc496edaf17f714c0fecd8b3eb79670207b Mon Sep 17 00:00:00 2001
From: Kees Cook <keescook@chromium.org>
Date: Tue, 26 Jan 2016 01:19:36 +0100
Subject: ARM: 8501/1: mm: flip priority of CONFIG_DEBUG_RODATA

The use of CONFIG_DEBUG_RODATA is generally seen as an essential part of
kernel self-protection:
http://www.openwall.com/lists/kernel-hardening/2015/11/30/13
Additionally, its name has grown to mean things beyond just rodata. To
get ARM closer to this, we ought to rearrange the names of the configs
that control how the kernel protects its memory. What was called
CONFIG_ARM_KERNMEM_PERMS is realy doing the work that other architectures
call CONFIG_DEBUG_RODATA.

This redefines CONFIG_DEBUG_RODATA to actually do the bulk of the
ROing (and NXing). In the place of the old CONFIG_DEBUG_RODATA, use
CONFIG_DEBUG_ALIGN_RODATA, since that's what the option does: adds
section alignment for making rodata explicitly NX, as arm does not split
the page tables like arm64 does without _ALIGN_RODATA.

Also adds human readable names to the sections so I could more easily
debug my typos, and makes CONFIG_DEBUG_RODATA default "y" for CPU_V7.

Results in /sys/kernel/debug/kernel_page_tables for each config state:

 # CONFIG_DEBUG_RODATA is not set
 # CONFIG_DEBUG_ALIGN_RODATA is not set

---[ Kernel Mapping ]---
0x80000000-0x80900000           9M     RW x  SHD
0x80900000-0xa0000000         503M     RW NX SHD

 CONFIG_DEBUG_RODATA=y
 CONFIG_DEBUG_ALIGN_RODATA=y

---[ Kernel Mapping ]---
0x80000000-0x80100000           1M     RW NX SHD
0x80100000-0x80700000           6M     ro x  SHD
0x80700000-0x80a00000           3M     ro NX SHD
0x80a00000-0xa0000000         502M     RW NX SHD

 CONFIG_DEBUG_RODATA=y
 # CONFIG_DEBUG_ALIGN_RODATA is not set

---[ Kernel Mapping ]---
0x80000000-0x80100000           1M     RW NX SHD
0x80100000-0x80a00000           9M     ro x  SHD
0x80a00000-0xa0000000         502M     RW NX SHD

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---
 arch/arm/kernel/vmlinux.lds.S | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

(limited to 'arch/arm/kernel/vmlinux.lds.S')

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 8b60fde5ce48..a6e395c53a48 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -8,7 +8,7 @@
 #include <asm/thread_info.h>
 #include <asm/memory.h>
 #include <asm/page.h>
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
 #include <asm/pgtable.h>
 #endif
 
@@ -94,7 +94,7 @@ SECTIONS
 		HEAD_TEXT
 	}
 
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
 	. = ALIGN(1<<SECTION_SHIFT);
 #endif
 
@@ -117,7 +117,7 @@ SECTIONS
 			ARM_CPU_KEEP(PROC_INFO)
 	}
 
-#ifdef CONFIG_DEBUG_RODATA
+#ifdef CONFIG_DEBUG_ALIGN_RODATA
 	. = ALIGN(1<<SECTION_SHIFT);
 #endif
 	RO_DATA(PAGE_SIZE)
@@ -153,7 +153,7 @@ SECTIONS
 	_etext = .;			/* End of text and rodata section */
 
 #ifndef CONFIG_XIP_KERNEL
-# ifdef CONFIG_ARM_KERNMEM_PERMS
+# ifdef CONFIG_DEBUG_RODATA
 	. = ALIGN(1<<SECTION_SHIFT);
 # else
 	. = ALIGN(PAGE_SIZE);
@@ -231,7 +231,7 @@ SECTIONS
 	__data_loc = ALIGN(4);		/* location in binary */
 	. = PAGE_OFFSET + TEXT_OFFSET;
 #else
-#ifdef CONFIG_ARM_KERNMEM_PERMS
+#ifdef CONFIG_DEBUG_RODATA
 	. = ALIGN(1<<SECTION_SHIFT);
 #else
 	. = ALIGN(THREAD_SIZE);
-- 
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