[PATCH] arm64: lib: use c string functions for KASAN support
From: Andrey Ryabinin <hidden>
Date: 2018-08-14 09:18:36
Also in:
lkml
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:
..
quoted hunk ↗ jump to hunk
Signed-off-by: Kyeongdon Kim <redacted> --- 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.