x86/mm/ptdump: Add address marker for KASAN shadow region

Annotate the KASAN shadow with address markers in page table
dump output:

$ cat /sys/kernel/debug/kernel_page_tables
...

---[ Vmemmap ]---
0xffffea0000000000-0xffffea0003000000          48M     RW         PSE     GLB NX pmd
0xffffea0003000000-0xffffea0004000000          16M                               pmd
0xffffea0004000000-0xffffea0005000000          16M     RW         PSE     GLB NX pmd
0xffffea0005000000-0xffffea0040000000         944M                               pmd
0xffffea0040000000-0xffffea8000000000         511G                               pud
0xffffea8000000000-0xffffec0000000000        1536G                               pgd
---[ KASAN shadow ]---
0xffffec0000000000-0xffffed0000000000           1T     ro                 GLB NX pte
0xffffed0000000000-0xffffed0018000000         384M     RW         PSE     GLB NX pmd
0xffffed0018000000-0xffffed0020000000         128M                               pmd
0xffffed0020000000-0xffffed0028200000         130M     RW         PSE     GLB NX pmd
0xffffed0028200000-0xffffed0040000000         382M                               pmd
0xffffed0040000000-0xffffed8000000000         511G                               pud
0xffffed8000000000-0xfffff50000000000        7680G                               pgd
0xfffff50000000000-0xfffffbfff0000000     7339776M     ro                 GLB NX pte
0xfffffbfff0000000-0xfffffbfff0200000           2M                               pmd
0xfffffbfff0200000-0xfffffbfff0a00000           8M     RW         PSE     GLB NX pmd
0xfffffbfff0a00000-0xfffffbffffe00000         244M                               pmd
0xfffffbffffe00000-0xfffffc0000000000           2M     ro                 GLB NX pte
---[ KASAN shadow end ]---
0xfffffc0000000000-0xffffff0000000000           3T                               pgd
---[ ESPfix Area ]---
...

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kasan-dev@googlegroups.com
Cc: Tobias Regnery <tobias.regnery@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Link: http://lkml.kernel.org/r/20170214100839.17186-2-aryabinin@virtuozzo.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/mm/dump_pagetables.c

@@ -18,6 +18,7 @@
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 
+#include <asm/kasan.h>
 #include <asm/pgtable.h>
 
 /*
@@ -51,6 +52,10 @@ enum address_markers_idx {
 	LOW_KERNEL_NR,
 	VMALLOC_START_NR,
 	VMEMMAP_START_NR,
+#ifdef CONFIG_KASAN
+	KASAN_SHADOW_START_NR,
+	KASAN_SHADOW_END_NR,
+#endif
 # ifdef CONFIG_X86_ESPFIX64
 	ESPFIX_START_NR,
 # endif
@@ -76,6 +81,10 @@ static struct addr_marker address_markers[] = {
 	{ 0/* PAGE_OFFSET */,   "Low Kernel Mapping" },
 	{ 0/* VMALLOC_START */, "vmalloc() Area" },
 	{ 0/* VMEMMAP_START */, "Vmemmap" },
+#ifdef CONFIG_KASAN
+	{ KASAN_SHADOW_START,	"KASAN shadow" },
+	{ KASAN_SHADOW_END,	"KASAN shadow end" },
+#endif
 # ifdef CONFIG_X86_ESPFIX64
 	{ ESPFIX_BASE_ADDR,	"ESPfix Area", 16 },
 # endif