[PATCH v2] arm64: kasan: add interceptors for strcmp/strncmp functions

[Kyeongdon Kim]

This patch declares strcmp/strncmp as weak symbols.
(2 of them are the most used string operations)

Original functions declared as weak and
strong ones in mm/kasan/kasan.c could replace them.

Assembly optimized strcmp/strncmp functions cannot detect KASan bug.
But, now we can detect them like the call trace below.

==================================================================
BUG: KASAN: use-after-free in platform_match+0x1c/0x5c at addr ffffffc0ad313500
Read of size 1 by task swapper/0/1
CPU: 3 PID: 1 Comm: swapper/0 Tainted: G    B           4.9.77+ #1
Hardware name: Generic (DT) based system
Call trace:
 dump_backtrace+0x0/0x2e0
 show_stack+0x14/0x1c
 dump_stack+0x88/0xb0
 kasan_object_err+0x24/0x7c
 kasan_report+0x2f0/0x484
 check_memory_region+0x20/0x14c
 strcmp+0x1c/0x5c
 platform_match+0x40/0xe4
 __driver_attach+0x40/0x130
 bus_for_each_dev+0xc4/0xe0
 driver_attach+0x30/0x3c
 bus_add_driver+0x2dc/0x328
 driver_register+0x118/0x160
 __platform_driver_register+0x7c/0x88
 alarmtimer_init+0x154/0x1e4
 do_one_initcall+0x184/0x1a4
 kernel_init_freeable+0x2ec/0x2f0
 kernel_init+0x18/0x10c
 ret_from_fork+0x10/0x50

In case of xtensa and x86_64 kasan, no need to use this patch now.

Signed-off-by: Kyeongdon Kim <kyeongdon.kim@xxxxxxx>
---
 arch/arm64/include/asm/string.h |  5 +++++
 arch/arm64/kernel/arm64ksyms.c  |  2 ++
 arch/arm64/kernel/image.h       |  2 ++
 arch/arm64/lib/strcmp.S         |  3 +++
 arch/arm64/lib/strncmp.S        |  3 +++
 mm/kasan/kasan.c                | 23 +++++++++++++++++++++++
 6 files changed, 38 insertions(+)

diff --git a/arch/arm64/include/asm/string.h b/arch/arm64/include/asm/string.h
index dd95d33..ab60349 100644
--- a/arch/arm64/include/asm/string.h
+++ b/arch/arm64/include/asm/string.h
@@ -24,9 +24,11 @@ extern char *strchr(const char *, int c);
 
 #define __HAVE_ARCH_STRCMP
 extern int strcmp(const char *, const char *);
+extern int __strcmp(const char *, const char *);
 
 #define __HAVE_ARCH_STRNCMP
 extern int strncmp(const char *, const char *, __kernel_size_t);
+extern int __strncmp(const char *, const char *, __kernel_size_t);
 
 #define __HAVE_ARCH_STRLEN
 extern __kernel_size_t strlen(const char *);
@@ -68,6 +70,9 @@ void memcpy_flushcache(void *dst, const void *src, size_t cnt);
 #define memmove(dst, src, len) __memmove(dst, src, len)
 #define memset(s, c, n) __memset(s, c, n)
 
+#define strcmp(cs, ct) __strcmp(cs, ct)
+#define strncmp(cs, ct, n) __strncmp(cs, ct, n)
+
 #ifndef __NO_FORTIFY
 #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
 #endif
diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c
index d894a20..10b1164 100644
--- a/arch/arm64/kernel/arm64ksyms.c
+++ b/arch/arm64/kernel/arm64ksyms.c
@@ -50,6 +50,8 @@ EXPORT_SYMBOL(strcmp);
 EXPORT_SYMBOL(strncmp);
 EXPORT_SYMBOL(strlen);
 EXPORT_SYMBOL(strnlen);
+EXPORT_SYMBOL(__strcmp);
+EXPORT_SYMBOL(__strncmp);
 EXPORT_SYMBOL(memset);
 EXPORT_SYMBOL(memcpy);
 EXPORT_SYMBOL(memmove);
diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
index a820ed0..5ef7a57 100644
--- a/arch/arm64/kernel/image.h
+++ b/arch/arm64/kernel/image.h
@@ -110,6 +110,8 @@ __efistub___flush_dcache_area	= KALLSYMS_HIDE(__pi___flush_dcache_area);
 __efistub___memcpy		= KALLSYMS_HIDE(__pi_memcpy);
 __efistub___memmove		= KALLSYMS_HIDE(__pi_memmove);
 __efistub___memset		= KALLSYMS_HIDE(__pi_memset);
+__efistub___strcmp		= KALLSYMS_HIDE(__pi_strcmp);
+__efistub___strncmp		= KALLSYMS_HIDE(__pi_strncmp);
 #endif
 
 __efistub__text			= KALLSYMS_HIDE(_text);
diff --git a/arch/arm64/lib/strcmp.S b/arch/arm64/lib/strcmp.S
index 471fe61..0dffef7 100644
--- a/arch/arm64/lib/strcmp.S
+++ b/arch/arm64/lib/strcmp.S
@@ -60,6 +60,8 @@ tmp3		.req	x9
 zeroones	.req	x10
 pos		.req	x11
 
+.weak strcmp
+ENTRY(__strcmp)
 ENTRY(strcmp)
 	eor	tmp1, src1, src2
 	mov	zeroones, #REP8_01
@@ -232,3 +234,4 @@ CPU_BE(	orr	syndrome, diff, has_nul )
 	sub	result, data1, data2, lsr #56
 	ret
 ENDPIPROC(strcmp)
+ENDPROC(__strcmp)
diff --git a/arch/arm64/lib/strncmp.S b/arch/arm64/lib/strncmp.S
index e267044..b2648c7 100644
--- a/arch/arm64/lib/strncmp.S
+++ b/arch/arm64/lib/strncmp.S
@@ -64,6 +64,8 @@ limit_wd	.req	x13
 mask		.req	x14
 endloop		.req	x15
 
+.weak strncmp
+ENTRY(__strncmp)
 ENTRY(strncmp)
 	cbz	limit, .Lret0
 	eor	tmp1, src1, src2
@@ -308,3 +310,4 @@ CPU_BE( orr	syndrome, diff, has_nul )
 	mov	result, #0
 	ret
 ENDPIPROC(strncmp)
+ENDPROC(__strncmp)
diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index c3bd520..61ad7f1 100644
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -304,6 +304,29 @@ void *memcpy(void *dest, const void *src, size_t len)
 
 	return __memcpy(dest, src, len);
 }
+#ifdef CONFIG_ARM64
+/*
+ * Arch arm64 use assembly variant for strcmp/strncmp,
+ * xtensa use inline asm operations and x86_64 use c one,
+ * so now this interceptors only for arm64 kasan.
+ */
+#undef strcmp
+int strcmp(const char *cs, const char *ct)
+{
+	check_memory_region((unsigned long)cs, 1, false, _RET_IP_);
+	check_memory_region((unsigned long)ct, 1, false, _RET_IP_);
+
+	return __strcmp(cs, ct);
+}
+#undef strncmp
+int strncmp(const char *cs, const char *ct, size_t len)
+{
+	check_memory_region((unsigned long)cs, len, false, _RET_IP_);
+	check_memory_region((unsigned long)ct, len, false, _RET_IP_);
+
+	return __strncmp(cs, ct, len);
+}
+#endif
 
 void kasan_alloc_pages(struct page *page, unsigned int order)
 {
-- 
2.6.2