[PATCH v3 4/6] Define the virtual space of KASan's shadow region

From: Abbott Liu
Date: Mon Apr 02 2018 - 08:25:14 EST

Define KASAN_SHADOW_OFFSET,KASAN_SHADOW_START and KASAN_SHADOW_END for arm
kernel address sanitizer.

+----+ 0xffffffff
| |
| |
| |
+----+ CONFIG_PAGE_OFFSET
| | | | |-> module virtual address space area.
| |/
+----+ MODULE_VADDR = KASAN_SHADOW_END
| | | | |-> the shadow area of kernel virtual address.
| |/
+----+ TASK_SIZE(start of kernel space) = KASAN_SHADOW_START the
| |\ shadow address of MODULE_VADDR
| | ---------------------+
| | |
+ + KASAN_SHADOW_OFFSET |-> the user space area. Kernel address
| | | sanitizer do not use this space.
| | ---------------------+
| |/
------ 0

1)KASAN_SHADOW_OFFSET:
This value is used to map an address to the corresponding shadow
address by the following formula:
shadow_addr = (address >> 3) + KASAN_SHADOW_OFFSET;

2)KASAN_SHADOW_START
This value is the MODULE_VADDR's shadow address. It is the start
of kernel virtual space.

3)KASAN_SHADOW_END
This value is the 0x100000000's shadow address. It is the end of
kernel addresssanitizer's shadow area. It is also the start of the
module area.

When enable kasan, the definition of TASK_SIZE is not an an 8-bit
rotated constant, so we need to modify the TASK_SIZE access code
in the *.s file.

Cc: Andrey Ryabinin <a.ryabinin@xxxxxxxxxxx>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Reviewed-by: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx>
Tested-by: Joel Stanley <joel@xxxxxxxxx>
Tested-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
Tested-by: Abbott Liu <liuwenliang@xxxxxxxxxx>
Signed-off-by: Abbott Liu <liuwenliang@xxxxxxxxxx>
---
arch/arm/include/asm/kasan_def.h | 64 ++++++++++++++++++++++++++++++++++++++++
arch/arm/include/asm/memory.h | 5 ++++
arch/arm/kernel/entry-armv.S | 5 ++--
arch/arm/kernel/entry-common.S | 9 ++++--
arch/arm/mm/init.c | 6 ++++
arch/arm/mm/mmu.c | 7 ++++-
6 files changed, 90 insertions(+), 6 deletions(-)
create mode 100644 arch/arm/include/asm/kasan_def.h

diff --git a/arch/arm/include/asm/kasan_def.h b/arch/arm/include/asm/kasan_def.h
new file mode 100644
index 0000000..7b7f424
--- /dev/null
+++ b/arch/arm/include/asm/kasan_def.h
@@ -0,0 +1,64 @@
+/*
+ * arch/arm/include/asm/kasan_def.h
+ *
+ * Copyright (c) 2018 Huawei Technologies Co., Ltd.
+ *
+ * Author: Abbott Liu <liuwenliang@xxxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __ASM_KASAN_DEF_H
+#define __ASM_KASAN_DEF_H
+
+#ifdef CONFIG_KASAN
+
+/*
+ * +----+ 0xffffffff
+ * | |
+ * | |
+ * | |
+ * +----+ CONFIG_PAGE_OFFSET
+ * | |\
+ * | | |-> module virtual address space area.
+ * | |/
+ * +----+ MODULE_VADDR = KASAN_SHADOW_END
+ * | |\
+ * | | |-> the shadow area of kernel virtual address.
+ * | |/
+ * +----+ TASK_SIZE(start of kernel space) = KASAN_SHADOW_START the
+ * | |\ shadow address of MODULE_VADDR
+ * | | ---------------------+
+ * | | |
+ * + + KASAN_SHADOW_OFFSET |-> the user space area. Kernel address
+ * | | | sanitizer do not use this space.
+ * | | ---------------------+
+ * | |/
+ * ------ 0
+ *
+ *1)KASAN_SHADOW_OFFSET:
+ * This value is used to map an address to the corresponding shadow
+ * address by the following formula:
+ * shadow_addr = (address >> 3) + KASAN_SHADOW_OFFSET;
+ *
+ * 2)KASAN_SHADOW_START
+ * This value is the MODULE_VADDR's shadow address. It is the start
+ * of kernel virtual space.
+ *
+ * 3) KASAN_SHADOW_END
+ * This value is the 0x100000000's shadow address. It is the end of
+ * kernel addresssanitizer's shadow area. It is also the start of the
+ * module area.
+ *
+ */
+
+#define KASAN_SHADOW_OFFSET (KASAN_SHADOW_END - (1<<29))
+
+#define KASAN_SHADOW_START ((KASAN_SHADOW_END >> 3) + KASAN_SHADOW_OFFSET)
+
+#define KASAN_SHADOW_END (UL(CONFIG_PAGE_OFFSET) - UL(SZ_16M))
+
+#endif
+#endif
diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
index 4966677..3ce1a9a 100644
--- a/arch/arm/include/asm/memory.h
+++ b/arch/arm/include/asm/memory.h
@@ -21,6 +21,7 @@
#ifdef CONFIG_NEED_MACH_MEMORY_H
#include <mach/memory.h>
#endif
+#include <asm/kasan_def.h>

/*
* Allow for constants defined here to be used from assembly code
@@ -37,7 +38,11 @@
* TASK_SIZE - the maximum size of a user space task.
* TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area
*/
+#ifndef CONFIG_KASAN
#define TASK_SIZE (UL(CONFIG_PAGE_OFFSET) - UL(SZ_16M))
+#else
+#define TASK_SIZE (KASAN_SHADOW_START)
+#endif
#define TASK_UNMAPPED_BASE ALIGN(TASK_SIZE / 3, SZ_16M)

/*
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 1752033..b4de9e4 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -183,7 +183,7 @@ ENDPROC(__und_invalid)

get_thread_info tsk
ldr r0, [tsk, #TI_ADDR_LIMIT]
- mov r1, #TASK_SIZE
+ ldr r1, =TASK_SIZE
str r1, [tsk, #TI_ADDR_LIMIT]
str r0, [sp, #SVC_ADDR_LIMIT]

@@ -437,7 +437,8 @@ ENDPROC(__fiq_abt)
@ if it was interrupted in a critical region. Here we
@ perform a quick test inline since it should be false
@ 99.9999% of the time. The rest is done out of line.
- cmp r4, #TASK_SIZE
+ ldr r0, =TASK_SIZE
+ cmp r4, r0
blhs kuser_cmpxchg64_fixup
#endif
#endif
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 3c4f887..78046de 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -51,7 +51,8 @@ ret_fast_syscall:
UNWIND(.cantunwind )
disable_irq_notrace @ disable interrupts
ldr r2, [tsk, #TI_ADDR_LIMIT]
- cmp r2, #TASK_SIZE
+ ldr r1, =TASK_SIZE
+ cmp r2, r1
blne addr_limit_check_failed
ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
@@ -81,7 +82,8 @@ ret_fast_syscall:
str r0, [sp, #S_R0 + S_OFF]! @ save returned r0
disable_irq_notrace @ disable interrupts
ldr r2, [tsk, #TI_ADDR_LIMIT]
- cmp r2, #TASK_SIZE
+ ldr r1, =TASK_SIZE
+ cmp r2, r1
blne addr_limit_check_failed
ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
@@ -116,7 +118,8 @@ ret_slow_syscall:
disable_irq_notrace @ disable interrupts
ENTRY(ret_to_user_from_irq)
ldr r2, [tsk, #TI_ADDR_LIMIT]
- cmp r2, #TASK_SIZE
+ ldr r1, =TASK_SIZE
+ cmp r2, r1
blne addr_limit_check_failed
ldr r1, [tsk, #TI_FLAGS]
tst r1, #_TIF_WORK_MASK
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index bd6f451..da11f61 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -538,6 +538,9 @@ void __init mem_init(void)
#ifdef CONFIG_MODULES
" modules : 0x%08lx - 0x%08lx (%4ld MB)\n"
#endif
+#ifdef CONFIG_KASAN
+ " kasan : 0x%08lx - 0x%08lx (%4ld MB)\n"
+#endif
" .text : 0x%p" " - 0x%p" " (%4td kB)\n"
" .init : 0x%p" " - 0x%p" " (%4td kB)\n"
" .data : 0x%p" " - 0x%p" " (%4td kB)\n"
@@ -558,6 +561,9 @@ void __init mem_init(void)
#ifdef CONFIG_MODULES
MLM(MODULES_VADDR, MODULES_END),
#endif
+#ifdef CONFIG_KASAN
+ MLM(KASAN_SHADOW_START, KASAN_SHADOW_END),
+#endif

MLK_ROUNDUP(_text, _etext),
MLK_ROUNDUP(__init_begin, __init_end),
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index e46a6a4..f5aa1de 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1251,9 +1251,14 @@ static inline void prepare_page_table(void)
/*
* Clear out all the mappings below the kernel image.
*/
- for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE)
+ for (addr = 0; addr < TASK_SIZE; addr += PMD_SIZE)
pmd_clear(pmd_off_k(addr));

+#ifdef CONFIG_KASAN
+ /*TASK_SIZE ~ MODULES_VADDR is the KASAN's shadow area -- skip over it*/
+ addr = MODULES_VADDR;
+#endif
+
#ifdef CONFIG_XIP_KERNEL
/* The XIP kernel is mapped in the module area -- skip over it */
addr = ((unsigned long)_exiprom + PMD_SIZE - 1) & PMD_MASK;
--
2.9.0