kaiser: kaiser_remove_mapping() move along the pgd

When removing the bogus comment from kaiser_remove_mapping(),
I really ought to have checked the extent of its bogosity: as
Neel points out, there is nothing to stop unmap_pud_range_nofree()
from continuing beyond the end of a pud (and starting in the wrong
position on the next).

Fix kaiser_remove_mapping() to constrain the extent and advance pgd
pointer correctly: use pgd_addr_end() macro as used throughout base
mm (but don't assume page-rounded start and size in this case).

But this bug was very unlikely to trigger in this backport: since
any buddy allocation is contained within a single pud extent, and
we are not using vmapped stacks (and are only mapping one page of
stack anyway): the only way to hit this bug here would be when
freeing a large modified ldt.

Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/mm/kaiser.c b/arch/x86/mm/kaiser.c
index fa1cb09..cc0950f 100644 (file)
--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -319,11 +319,13 @@ void kaiser_remove_mapping(unsigned long start, unsigned long size)
        extern void unmap_pud_range_nofree(pgd_t *pgd,
                                unsigned long start, unsigned long end);
        unsigned long end = start + size;
-       unsigned long addr;
+       unsigned long addr, next;
+       pgd_t *pgd;
 
-       for (addr = start; addr < end; addr += PGDIR_SIZE) {
-               pgd_t *pgd = native_get_shadow_pgd(pgd_offset_k(addr));
-               unmap_pud_range_nofree(pgd, addr, end);
+       pgd = native_get_shadow_pgd(pgd_offset_k(start));
+       for (addr = start; addr < end; pgd++, addr = next) {
+               next = pgd_addr_end(addr, end);
+               unmap_pud_range_nofree(pgd, addr, next);
        }
 }