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>

4 files changed, 62 insertions, 1 deletions

diff --git a/arch/xtensa/include/asm/kasan.h b/arch/xtensa/include/asm/kasan.h
new file mode 100644
index 000000000000..54be80876e57
--- /dev/null
+++ b/arch/xtensa/include/asm/kasan.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_KASAN_H
+#define __ASM_KASAN_H
+
+#ifndef __ASSEMBLY__
+
+#ifdef CONFIG_KASAN
+
+#include <linux/kernel.h>
+#include <linux/sizes.h>
+#include <asm/kmem_layout.h>
+
+/* Start of area covered by KASAN */
+#define KASAN_START_VADDR __XTENSA_UL_CONST(0x90000000)
+/* Start of the shadow map */
+#define KASAN_SHADOW_START (XCHAL_PAGE_TABLE_VADDR + XCHAL_PAGE_TABLE_SIZE)
+/* Size of the shadow map */
+#define KASAN_SHADOW_SIZE (-KASAN_START_VADDR >> KASAN_SHADOW_SCALE_SHIFT)
+/* Offset for mem to shadow address transformation */
+#define KASAN_SHADOW_OFFSET __XTENSA_UL_CONST(CONFIG_KASAN_SHADOW_OFFSET)
+
+void __init kasan_early_init(void);
+void __init kasan_init(void);
+
+#else
+
+static inline void kasan_early_init(void)
+{
+}
+
+static inline void kasan_init(void)
+{
+}
+
+#endif
+#endif
+#endif
diff --git a/arch/xtensa/include/asm/kmem_layout.h b/arch/xtensa/include/asm/kmem_layout.h
index 28f9260a766c..2317c835a4db 100644
--- a/arch/xtensa/include/asm/kmem_layout.h
+++ b/arch/xtensa/include/asm/kmem_layout.h
@@ -71,7 +71,11 @@
 
 #endif
 
+#ifndef CONFIG_KASAN
 #define KERNEL_STACK_SHIFT	13
+#else
+#define KERNEL_STACK_SHIFT	15
+#endif
 #define KERNEL_STACK_SIZE	(1 << KERNEL_STACK_SHIFT)
 
 #endif
diff --git a/arch/xtensa/include/asm/pgtable.h b/arch/xtensa/include/asm/pgtable.h
index 30dd5b2e4ad5..38802259978f 100644
--- a/arch/xtensa/include/asm/pgtable.h
+++ b/arch/xtensa/include/asm/pgtable.h
@@ -12,9 +12,9 @@
 #define _XTENSA_PGTABLE_H
 
 #define __ARCH_USE_5LEVEL_HACK
-#include <asm-generic/pgtable-nopmd.h>
 #include <asm/page.h>
 #include <asm/kmem_layout.h>
+#include <asm-generic/pgtable-nopmd.h>
 
 /*
  * We only use two ring levels, user and kernel space.
@@ -170,6 +170,7 @@
 #define PAGE_SHARED_EXEC \
 	__pgprot(_PAGE_PRESENT | _PAGE_USER | _PAGE_WRITABLE | _PAGE_HW_EXEC)
 #define PAGE_KERNEL	   __pgprot(_PAGE_PRESENT | _PAGE_HW_WRITE)
+#define PAGE_KERNEL_RO	   __pgprot(_PAGE_PRESENT)
 #define PAGE_KERNEL_EXEC   __pgprot(_PAGE_PRESENT|_PAGE_HW_WRITE|_PAGE_HW_EXEC)
 
 #if (DCACHE_WAY_SIZE > PAGE_SIZE)
diff --git a/arch/xtensa/include/asm/string.h b/arch/xtensa/include/asm/string.h
index 8d5d9dfadb09..586bad9fe187 100644
--- a/arch/xtensa/include/asm/string.h
+++ b/arch/xtensa/include/asm/string.h
@@ -108,14 +108,33 @@ static inline int strncmp(const char *__cs, const char *__ct, size_t __n)
 
 #define __HAVE_ARCH_MEMSET
 extern void *memset(void *__s, int __c, size_t __count);
+extern void *__memset(void *__s, int __c, size_t __count);
 
 #define __HAVE_ARCH_MEMCPY
 extern void *memcpy(void *__to, __const__ void *__from, size_t __n);
+extern void *__memcpy(void *__to, __const__ void *__from, size_t __n);
 
 #define __HAVE_ARCH_MEMMOVE
 extern void *memmove(void *__dest, __const__ void *__src, size_t __n);
+extern void *__memmove(void *__dest, __const__ void *__src, size_t __n);
 
 /* Don't build bcopy at all ...  */
 #define __HAVE_ARCH_BCOPY
 
+#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
+
+/*
+ * For files that are not instrumented (e.g. mm/slub.c) we
+ * should use not instrumented version of mem* functions.
+ */
+
+#define memcpy(dst, src, len) __memcpy(dst, src, len)
+#define memmove(dst, src, len) __memmove(dst, src, len)
+#define memset(s, c, n) __memset(s, c, n)
+
+#ifndef __NO_FORTIFY
+#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
+#endif
+#endif
+
 #endif	/* _XTENSA_STRING_H */