Hi Paul, On Thu, Aug 15, 2019 at 11:27:51AM -0700, Paul Walmsley wrote: > On Thu, 15 Aug 2019, Nick Hu wrote: > > > On Wed, Aug 14, 2019 at 10:03:39AM -0700, Paul Walmsley wrote: > > > > > Thanks for the explanation. What do you think about Palmer's idea to > > > define a generic C set of KASAN string operations, derived from the > > > newlib > > > code? > > > > That sounds good to me. But it should be another topic. We need to > > investigate > > it further about replacing something generic and fundamental in lib/string.c > > with newlib C functions. Some blind spots may exist. So I suggest, let's > > consider KASAN for now. > > OK. Here is the problem for us as maintainers. You, Palmer, and I all > agree that a C-language version would be better. We'd rather not merge a > pure assembly-language version unless it had significant advantages, and > right now we're not anticipating that. So that suggests that a C-language > memmove() is the right way to go. > > But if we merge a C-language memmove() into arch/riscv, other kernel > developers would probably ask us why we're doing that, since there's > nothing RISC-V-specific about it. So do you think you might reconsider > sending patches to add a generic C-language memmove()? > > > - Paul
About pushing mem*() generic, let's start with the reason why in the first place KASAN needs re-implement its own string operations: In mm/kasan/common.c: #undef memset void *memset(void *addr, int c, size_t len) { check_memory_region((unsigned long)addr, len, true, _RET_IP_); return __memset(addr, c, len); } KASAN would call the string operations with the prefix '__', which should be just an alias to the proper one. In the past, every architecture that supports KASAN does this in assembly. E.g. ARM64: In arch/arm64/lib/memset.S: ENTRY(__memset) ENTRY(memset) ... ... EXPORT_SYMBOL(memset) EXPORT_SYMBOL(__memset) // export this as an alias In arch/arm64/include/asm/string.h #define __HAVE_ARCH_MEMSET extern void *memset(void *, int, __kernel_size_t); extern void *__memset(void *, int, __kernel_size_t); Now, if we are going to replace the current string operations with newlib ones and let KASAN use them, we must provide something like this: In lib/string.c: void *___memset(...) { ... } In include/linux/string.h: #ifndef __HAVE_ARCH_MEMCPY #ifdef CONFIG_KASAN static inline void* __memset(...) { ___memset(...); } extern void memset(...); // force those who include this header uses the memset wrapped by KASAN #else static inline void *memset(...) { ___memset(...); } #endif #endif Does this look OK to you? Nick