Re: [Qemu-devel] [PATCH] mmap: add check if requested memory area fits target address space

[Kirill A. Shutemov]

On Mon, Nov 10, 2008 at 04:30:39AM +0100, andrzej zaborowski wrote:
> Sorry to resurrect this old thread, I still can't convince myself.
> 
> 2008/10/27 Kirill A. Shutemov <address@hidden>:
> > On Mon, Oct 27, 2008 at 08:37:39PM +0100, andrzej zaborowski wrote:
> >> 2008/10/27 Kirill A. Shutemov <address@hidden>:
> >> > On Mon, Oct 27, 2008 at 02:08:52PM +0100, andrzej zaborowski wrote:
> >> >> On 17/10/2008, Kirill A. Shutemov <address@hidden> wrote:
> >> >> > Signed-off-by: Kirill A. Shutemov <address@hidden>
> >> >> >  ---
> >> >> >   linux-user/mmap.c |    5 +++++
> >> >> >   1 files changed, 5 insertions(+), 0 deletions(-)
> >> >> >
> >> >> >  diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> >> >> >  index bc20f4b..9a2f355 100644
> >> >> >  --- a/linux-user/mmap.c
> >> >> >  +++ b/linux-user/mmap.c
> >> >> >  @@ -388,6 +388,11 @@ abi_long target_mmap(abi_ulong start, abi_ulong 
> >> >> > len, int prot,
> >> >> >          end = start + len;
> >> >> >          real_end = HOST_PAGE_ALIGN(end);
> >> >> >
> >> >> >  +        if ((unsigned long)start + len > (abi_ulong) -1) {
> >> >> >  +            errno = EINVAL;
> >> >> >  +            goto fail;
> >> >> >  +        }
> >> >>
> >> >> I'm being picky but this would prevent the last byte from being used?
> >> >> :p  (or the last page because len is aligned?)
> >> >
> >> > No, it returns error if start + len is more than 0xFFFFFFFF (32-bit
> >> > target).
> >> >
> >> >>
> >> >> I'm not sure unsigned long is the best choice.
> >> >
> >> > Why?
> >>
> >> I may be misunderstanding but I think the range of valid addresses
> >> should depend on target word size, not host (even if the combination
> >> where it matters is not yet supported).
> >
> > start + len can be more than 0xFFFFFFFF ((abi_ulong) -1) on 32-bit targets,
> > so we should use host's long.
> >
> >> On a 32-bit host the condition is always false.
> >
> > It's ok. It can be true, only on 64-bit host.
> 
> Let's say we have a 32-bit host and target, the call receives start ==
> 0xffff0050 and len == 0x100000, the check passes, when it shouldn't
> (?).  On a 64-bit host it would fail, but this check should be
> independent of the host type.
> (It'll probably fail later in the host mmap() -- but in the meantime
> mmap_frag() might succeed for example)

mmap_frag() will not be called if host mmap() fail. mmap can fail on many
conditions, it's one of them.

Probably, I should add comment to this check, that it's for 64-bit host
only. Ok?

-- 
Regards,  Kirill A. Shutemov
 + Belarus, Minsk
 + ALT Linux Team, http://www.altlinux.com/

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