On Thu, Oct 12, 2017 at 11:27:40AM +0000, Liuwenliang (Lamb) wrote:
> >> - I don't understand why this is necessary. memory_is_poisoned_16()
> >> already handles unaligned addresses?
> >>
> >> - If it's needed on ARM then presumably it will be needed on other
> >> architectures, so CONFIG_ARM is insufficiently general.
> >>
> >> - If the present memory_is_poisoned_16() indeed doesn't work on ARM,
> >> it would be better to generalize/fix it in some fashion rather than
> >> creating a new variant of the function.
>
>
> >Yes, I think it will be better to fix the current function rather then
> >have 2 slightly different copies with ifdef's.
> >Will something along these lines work for arm? 16-byte accesses are
> >not too common, so it should not be a performance problem. And
> >probably modern compilers can turn 2 1-byte checks into a 2-byte check
> >where safe (x86).
>
> >static __always_inline bool memory_is_poisoned_16(unsigned long addr)
> >{
> > u8 *shadow_addr = (u8 *)kasan_mem_to_shadow((void *)addr);
> >
> > if (shadow_addr[0] || shadow_addr[1])
> > return true;
> > /* Unaligned 16-bytes access maps into 3 shadow bytes. */
> > if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
> > return memory_is_poisoned_1(addr + 15);
> > return false;
> >}
>
> Thanks for Andrew Morton and Dmitry Vyukov's review.
> If the parameter addr=0xc0000008, now in function:
> static __always_inline bool memory_is_poisoned_16(unsigned long addr)
> {
> --- //shadow_addr = (u16 *)(KASAN_OFFSET+0x18000001(=0xc0000008>>3)) is not
> --- // unsigned by 2 bytes.
> u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
>
> /* Unaligned 16-bytes access maps into 3 shadow bytes. */
> if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
> return *shadow_addr || memory_is_poisoned_1(addr + 15);
> ---- //here is going to be error on arm, specially when kernel has not finished yet.
> ---- //Because the unsigned accessing cause DataAbort Exception which is not
> ---- //initialized when kernel is starting.
> return *shadow_addr;
> }
>
> I also think it is better to fix this problem.
What about using get_unaligned() ?
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