It''s a bug. I moved the zeroing before get_page_and_type as those
entries could contain garbage in some cases. I forgot to hoist an
appropriate ownership check at the same time. :-)
I''ll fix that...
-- Keir
> It seems to me that set_gdt in xen/arch/x86/x86_32/mm.c could allow a
> domain to partially zero a page that it doesn''t own:
>
> long set_gdt(struct domain *d,
> unsigned long *frames,
> unsigned int entries)
> {
> /* NB. There are 512 8-byte entries per GDT page. */
> int i, nr_pages = (entries + 511) / 512;
> struct desc_struct *vgdt;
>
> vgdt = map_domain_mem(frames[0] << PAGE_SHIFT);
> memset( vgdt + FIRST_RESERVED_GDT_ENTRY, 0,
> NR_RESERVED_GDT_ENTRIES*8);
>
> /* Check the new GDT. */
> for ( i = 0; i < nr_pages; i++ )
> {
> if ( unlikely(frames[i] >= max_page) ||
> unlikely(!get_page_and_type(&frame_table[frames[i]],
> d, PGT_gdt_page)) )
> goto fail;
> }
>
> Xen doesn''t seem to check whether the list of pages specified in
> frames[] belongs to the calling domain until get_page_and_type is
> called, but Xen zeroes the reserved GDT entries in the first specified
> page before this. I don''t see any checks in do_set_gdt either.
>
> Am I missing something, or is this a bug?
>
> --Michael Vrable
>
>
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