arm64: kasan: Increase stack size for KASAN_EXTRA

If the kernel is configured with KASAN_EXTRA, the stack size is
increased significantly due to setting the GCC -fstack-reuse option to
"none" [1]. As a result, it can trigger a stack overrun quite often with
32k stack size compiled using GCC 8. For example, this reproducer

  https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise06.c

can trigger a "corrupted stack end detected inside scheduler" very
reliably with CONFIG_SCHED_STACK_END_CHECK enabled. There are other
reports at:

  https://lore.kernel.org/lkml/1542144497.12945.29.camel@gmx.us/
  https://lore.kernel.org/lkml/721E7B42-2D55-4866-9C1A-3E8D64F33F9C@gmx.us/

There are just too many functions that could have a large stack with
KASAN_EXTRA due to large local variables that have been called over and
over again without being able to reuse the stacks. Some noticiable ones
are,

size
7536 shrink_inactive_list
7440 shrink_page_list
6560 fscache_stats_show
3920 jbd2_journal_commit_transaction
3216 try_to_unmap_one
3072 migrate_page_move_mapping
3584 migrate_misplaced_transhuge_page
3920 ip_vs_lblcr_schedule
4304 lpfc_nvme_info_show
3888 lpfc_debugfs_nvmestat_data.constprop

There are other 49 functions over 2k in size while compiling kernel with
"-Wframe-larger-than=" on this machine. Hence, it is too much work to
change Makefiles for each object to compile without
-fsanitize-address-use-after-scope individually.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715#c23Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/memory.h

@@ -76,12 +76,17 @@
 /*
  * KASAN requires 1/8th of the kernel virtual address space for the shadow
  * region. KASAN can bloat the stack significantly, so double the (minimum)
- * stack size when KASAN is in use.
+ * stack size when KASAN is in use, and then double it again if KASAN_EXTRA is
+ * on.
  */
 #ifdef CONFIG_KASAN
 #define KASAN_SHADOW_SCALE_SHIFT 3
 #define KASAN_SHADOW_SIZE	(UL(1) << (VA_BITS - KASAN_SHADOW_SCALE_SHIFT))
+#ifdef CONFIG_KASAN_EXTRA
+#define KASAN_THREAD_SHIFT	2
+#else
 #define KASAN_THREAD_SHIFT	1
+#endif /* CONFIG_KASAN_EXTRA */
 #else
 #define KASAN_SHADOW_SIZE	(0)
 #define KASAN_THREAD_SHIFT	0