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[PATCH] mm: pte_offset_map_lock loops

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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>
This commit is contained in:
Hugh Dickins
2005-10-29 18:16:27 -07:00
committed by Linus Torvalds
parent 8f4e2101fd
commit 705e87c0c3
7 changed files with 30 additions and 47 deletions
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7
mm/mprotect.c
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@@ -29,8 +29,9 @@ static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
unsigned long addr, unsigned long end, pgprot_t newprot)
{
pte_t *pte;
spinlock_t *ptl;
pte = pte_offset_map(pmd, addr);
pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
do {
if (pte_present(*pte)) {
pte_t ptent;
@@ -44,7 +45,7 @@ static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
lazy_mmu_prot_update(ptent);
}
} while (pte++, addr += PAGE_SIZE, addr != end);
pte_unmap(pte - 1);
pte_unmap_unlock(pte - 1, ptl);
}
static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
@@ -88,7 +89,6 @@ static void change_protection(struct vm_area_struct *vma,
BUG_ON(addr >= end);
pgd = pgd_offset(mm, addr);
flush_cache_range(vma, addr, end);
spin_lock(&mm->page_table_lock);
do {
next = pgd_addr_end(addr, end);
if (pgd_none_or_clear_bad(pgd))
@@ -96,7 +96,6 @@ static void change_protection(struct vm_area_struct *vma,
change_pud_range(mm, pgd, addr, next, newprot);
} while (pgd++, addr = next, addr != end);
flush_tlb_range(vma, start, end);
spin_unlock(&mm->page_table_lock);
}
static int