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

[Dmitry Vyukov]

On Mon, Sep 3, 2018 at 11:02 AM, Kyeongdon Kim <kyeongdon.kim@xxxxxxx> wrote:
> Dear all,
>
> Could anyone review this and provide me appropriate approach ?
> I think str[n]cmp are frequently used functions so I believe very useful w/
> arm64 KASAN.

Hi Kyeongdon,

Please add tests for this to lib/test_kasan.c.

> On 2018-08-23 ìí 5:56, Kyeongdon Kim wrote:
>>
>> 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
>
>