On Mon, 2019-09-30 at 10:57 +0200, Marc Gonzalez wrote:
> On 30/09/2019 06:36, Walter Wu wrote:
>
> > bool check_memory_region(unsigned long addr, size_t size, bool write,
> > unsigned long ret_ip)
> > {
> > + if (long(size) < 0) {
> > + kasan_report_invalid_size(src, dest, len, _RET_IP_);
> > + return false;
> > + }
> > +
> > return check_memory_region_inline(addr, size, write, ret_ip);
> > }
>
> Is it expected that memcpy/memmove may sometimes (incorrectly) be passed
> a negative value? (It would indeed turn up as a "large" size_t)
>
> IMO, casting to long is suspicious.
>
> There seem to be some two implicit assumptions.
>
> 1) size >= ULONG_MAX/2 is invalid input
> 2) casting a size >= ULONG_MAX/2 to long yields a negative value
>
> 1) seems reasonable because we can't copy more than half of memory to
> the other half of memory. I suppose the constraint could be even tighter,
> but it's not clear where to draw the line, especially when considering
> 32b vs 64b arches.
>
> 2) is implementation-defined, and gcc works "as expected" (clang too
> probably) https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html
>
> A comment might be warranted to explain the rationale.
> Regards.
Thanks for your suggestion.
Yes, It is passed a negative value issue in memcpy/memmove/memset.
Our current idea should be assumption 1 and only consider 64b arch,
because KASAN only supports 64b. In fact, we really can't use so much
memory in 64b arch. so assumption 1 make sense.
