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| author |   Hugh Dickins <hugh@veritas.com> | 2005-10-29 18:16:27 -0700 |
|---|---|---|
| committer |   Linus Torvalds <torvalds@g5.osdl.org> | 2005-10-29 21:40:40 -0700 |
| commit | 705e87c0c3c38424f7f30556c85bc20e808d2f59 (patch) | |
| tree | 7a237e6266f4801385e1226cc497b47e3a2458bd /include/asm-i386 | |
| parent | [PATCH] mm: page fault handler locking (diff) | |
| download | linux-dev-705e87c0c3c38424f7f30556c85bc20e808d2f59.tar.xz linux-dev-705e87c0c3c38424f7f30556c85bc20e808d2f59.zip | |
[PATCH] mm: pte_offset_map_lock loops
Convert those common loops using page_table_lock on the outside and
pte_offset_map within to use just pte_offset_map_lock within instead.
These all hold mmap_sem (some exclusively, some not), so at no level can a
page table be whipped away from beneath them. But whereas pte_alloc loops
tested with the "atomic" pmd_present, these loops are testing with pmd_none,
which on i386 PAE tests both lower and upper halves.
That's now unsafe, so add a cast into pmd_none to test only the vital lower
half: we lose a little sensitivity to a corrupt middle directory, but not
enough to worry about. It appears that i386 and UML were the only
architectures vulnerable in this way, and pgd and pud no problem.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/asm-i386')
| -rw-r--r-- | include/asm-i386/pgtable.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/include/asm-i386/pgtable.h b/include/asm-i386/pgtable.h index d101ac414f07..0e3ec809352d 100644 --- a/include/asm-i386/pgtable.h +++ b/include/asm-i386/pgtable.h @@ -203,7 +203,8 @@ extern unsigned long pg0[]; #define pte_present(x) ((x).pte_low & (_PAGE_PRESENT | _PAGE_PROTNONE)) #define pte_clear(mm,addr,xp) do { set_pte_at(mm, addr, xp, __pte(0)); } while (0) -#define pmd_none(x) (!pmd_val(x)) +/* To avoid harmful races, pmd_none(x) should check only the lower when PAE */ +#define pmd_none(x) (!(unsigned long)pmd_val(x)) #define pmd_present(x) (pmd_val(x) & _PAGE_PRESENT) #define pmd_clear(xp) do { set_pmd(xp, __pmd(0)); } while (0) #define pmd_bad(x) ((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE) |