[Qemu-devel] Re: linux-user issues

[malc <av1474@comtv.ru>]

On Sun, 14 Mar 2010, Paul Brook wrote:

> > On Sat, 13 Mar 2010, Paul Brook wrote:
> > > > a) elfload.c:859
> > > >
> > > >    #define TARGET_ELF_PAGESTART(_v) ((_v) & ~(unsigned
> > > >  long)(TARGET_ELF_EXEC_PAGESIZE-1))
> > > >
> > > >    This means that for 64bit guest on a 32bit host the _v's value is
> > > >    silently reduced to 32bit, the cast should be abi_ulong.
> > > >
> > > > b) mmap.c:428
> > > >
> > > >    real_start = start & qemu_host_page_mask;
> > > >
> > > >    Same thing basically qemu_host_page_mask is unsigned long and so
> > > >    the upper bits are sliently cleared. Again qemu_host_page_mask
> > > >    should probably be abi_ulong.
> > > >
> > > > The above two make elf binary with one of the segments above 4G load
> > > > and run on 32bit guest only to fail well into execution and without
> > > > any indication that it shouldn't have been allowed to run in the first
> > > > place.
> > >
> > > I'd be amazed if these are the only two issues, and expect 64-bit guests
> > > on 32-bit hosts to be generally unsafe.
> > 
> > These are the two issues i've been bitten by while trying to solve
> > x86_64's far jumps, if you are okay with code silently misbehaving
> > fine by me.
> 
> I never said this was ok behavior. Only that you've probably only discovered 
> the tip of the iceberg.

Even on this path (mmap one) it's indeed not, further bellow there are
yet more truncations due to improperly sized and's. Furthermore the
abi_ulong sized `start' argument is passed to mmap without ever
checking if it fits 32bit, question is what to do about it.

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