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Received: from [172.16.25.12] (185.231.240.5) by AM0PR08MB3249.eurprd08.prod.outlook.com (2603:10a6:208:5e::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1038.20; Tue, 14 Aug 2018 09:18:26 +0000 Subject: Re: [PATCH] arm64: lib: use c string functions for KASAN support To: Kyeongdon Kim , catalin.marinas@arm.com, glider@google.com, dvyukov@google.com Cc: will.deacon@arm.com, Jason@zx2c4.com, gregkh@linuxfoundation.org, mingo@kernel.org, peterz@infradead.org, mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <1534233322-106271-1-git-send-email-kyeongdon.kim@lge.com> From: Andrey Ryabinin Message-ID: Date: Tue, 14 Aug 2018 12:18:32 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <1534233322-106271-1-git-send-email-kyeongdon.kim@lge.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US 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X-Microsoft-Exchange-Diagnostics: 1;AM0PR08MB3249;20:HcYBr6y3gnTYkfHTWy9BDlQQNLTL3Ucie5Xe32dvXYhEIxtVCnGf4yUvvUnS0tgAJScv87kZynLyAUF7Td56ecjxw0QcObEY6ty/6w/tubHwlx4vv/OGXC1RX02uovxorzmsgpNU7RNpWgRw+wvaGCgO90F4o9ah9hXoM8QDas0= X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Aug 2018 09:18:26.6941 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6c2075d4-ec0d-418a-775f-08d601c6e51c X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR08MB3249 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/14/2018 10:55 AM, Kyeongdon Kim wrote: > Assembly optimized string functions cannot detect KASan bug. > This might have been the intention of the original author. > (not too much important to catch) > > But, I found the obvious uaf problem in strcmp() function. > - in this case, using 32bit KASan patchset helps > > Since I used c string function, I believe I could find this bug. > After using the patch, can see the report & backtrace the below: > .. > > Signed-off-by: Kyeongdon Kim > --- > arch/arm64/include/asm/string.h | 2 ++ > arch/arm64/kernel/arm64ksyms.c | 2 ++ > arch/arm64/lib/Makefile | 8 +++++--- > 3 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/string.h b/arch/arm64/include/asm/string.h > index dd95d33..5c5219a 100644 > --- a/arch/arm64/include/asm/string.h > +++ b/arch/arm64/include/asm/string.h > @@ -16,6 +16,7 @@ > #ifndef __ASM_STRING_H > #define __ASM_STRING_H > > +#if !defined(CONFIG_KASAN) > #define __HAVE_ARCH_STRRCHR > extern char *strrchr(const char *, int c); > > @@ -33,6 +34,7 @@ extern __kernel_size_t strlen(const char *); > > #define __HAVE_ARCH_STRNLEN > extern __kernel_size_t strnlen(const char *, __kernel_size_t); > +#endif > > #define __HAVE_ARCH_MEMCPY > extern void *memcpy(void *, const void *, __kernel_size_t); > diff --git a/arch/arm64/kernel/arm64ksyms.c b/arch/arm64/kernel/arm64ksyms.c > index d894a20..eb9bf20 100644 > --- a/arch/arm64/kernel/arm64ksyms.c > +++ b/arch/arm64/kernel/arm64ksyms.c > @@ -44,12 +44,14 @@ EXPORT_SYMBOL(__arch_copy_in_user); > EXPORT_SYMBOL(memstart_addr); > > /* string / mem functions */ > +#if !defined(CONFIG_KASAN) > EXPORT_SYMBOL(strchr); > EXPORT_SYMBOL(strrchr); > EXPORT_SYMBOL(strcmp); > EXPORT_SYMBOL(strncmp); > EXPORT_SYMBOL(strlen); > EXPORT_SYMBOL(strnlen); > +#endif > EXPORT_SYMBOL(memset); > EXPORT_SYMBOL(memcpy); > EXPORT_SYMBOL(memmove); > diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile > index 68755fd..aa2d457 100644 > --- a/arch/arm64/lib/Makefile > +++ b/arch/arm64/lib/Makefile > @@ -2,9 +2,11 @@ > lib-y := clear_user.o delay.o copy_from_user.o \ > copy_to_user.o copy_in_user.o copy_page.o \ > clear_page.o memchr.o memcpy.o memmove.o memset.o \ > - memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \ > - strchr.o strrchr.o tishift.o > - > + memcmp.o tishift.o > +ifndef CONFIG_KASAN > +lib-y := strcmp.o strncmp.o strlen.o strnlen.o \ > + strchr.o strrchr.o > +endif I think, this won't even compile. EFI needs some of these functions, and it can't use instrumented and not position independent variants. The easiest solution I see, is to not exclude these sting functions, but declare them as weak. In that case, EFI stub should pick up assembly variant and the kernel will use the C one.