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Subject[PATCH v2] arm64: kasan: add interceptors for strcmp/strncmp functions
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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@lge.com>
---
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
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