xtensa: add support for KASAN

Cover kernel addresses above 0x90000000 by the shadow map. Enable
HAVE_ARCH_KASAN when MMU is enabled. Provide kasan_early_init that fills
shadow map with writable copies of kasan_zero_page. Call
kasan_early_init right after mmu initialization in the setup_arch.
Provide kasan_init that allocates proper shadow map pages from the
memblock and puts these pages into the shadow map for addresses from
VMALLOC area to the end of KSEG. Call kasan_init right after memblock
initialization. Don't use KASAN for the boot code, MMU and KASAN
initialization and page fault handler. Make kernel stack size 4 times
larger when KASAN is enabled to avoid stack overflows.
GCC 7.3, 8 or newer is required to build the xtensa kernel with KASAN.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/xtensa/mm/init.c b/arch/xtensa/mm/init.c
index 6fc1cb093fb3..0d980f05da82 100644
--- a/arch/xtensa/mm/init.c
+++ b/arch/xtensa/mm/init.c
@@ -100,6 +100,9 @@ void __init mem_init(void)
 
         mem_init_print_info(NULL);
         pr_info("virtual kernel memory layout:\n"
+#ifdef CONFIG_KASAN
+                "    kasan   : 0x%08lx - 0x%08lx  (%5lu MB)\n"
+#endif
 #ifdef CONFIG_MMU
                 "    vmalloc : 0x%08lx - 0x%08lx  (%5lu MB)\n"
 #endif
@@ -108,6 +111,10 @@ void __init mem_init(void)
                 "    fixmap  : 0x%08lx - 0x%08lx  (%5lu kB)\n"
 #endif
                 "    lowmem  : 0x%08lx - 0x%08lx  (%5lu MB)\n",
+#ifdef CONFIG_KASAN
+                KASAN_SHADOW_START, KASAN_SHADOW_START + KASAN_SHADOW_SIZE,
+                KASAN_SHADOW_SIZE >> 20,
+#endif
 #ifdef CONFIG_MMU
                 VMALLOC_START, VMALLOC_END,
                 (VMALLOC_END - VMALLOC_START) >> 20,