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uprobes: __replace_page() should not use page_address_in_vma()

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page_address_in_vma(old_page) in __replace_page() is ugly and
wrong. The caller already knows the correct virtual address,
this page was found by get_user_pages(vaddr).

However, page_address_in_vma() can actually fail if
page->mapping was cleared by __delete_from_page_cache() after
get_user_pages() returns. But this means the race with page
reclaim, write_opcode() should not fail, it should retry and
read this page again. Probably the race with remove_mapping() is
not possible due to page_freeze_refs() logic, but afaics at
least shmem_writepage()->shmem_delete_from_page_cache() can
clear ->mapping.

We could change __replace_page() to return -EAGAIN in this case,
but it would be better to simply use the caller's vaddr and rely
on page_check_address().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120729182216.GA20311@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Oleg Nesterov 2012-07-29 20:22:16 +02:00 committed by Ingo Molnar
parent f403072c61
commit c517ee744b
1 changed files with 4 additions and 7 deletions
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11
kernel/events/uprobes.c
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@ -127,22 +127,19 @@ static loff_t vma_address(struct vm_area_struct *vma, loff_t offset)
* based on replace_page in mm/ksm.c
*
* @vma: vma that holds the pte pointing to page
* @addr: address the old @page is mapped at
* @page: the cowed page we are replacing by kpage
* @kpage: the modified page we replace page by
*
* Returns 0 on success, -EFAULT on failure.
*/
static int __replace_page(struct vm_area_struct *vma, struct page *page, struct page *kpage)
static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
struct page *page, struct page *kpage)
{
struct mm_struct *mm = vma->vm_mm;
unsigned long addr;
spinlock_t *ptl;
pte_t *ptep;
addr = page_address_in_vma(page, vma);
if (addr == -EFAULT)
return -EFAULT;
ptep = page_check_address(page, mm, addr, &ptl, 0);
if (!ptep)
return -EAGAIN;
@ -243,7 +240,7 @@ retry:
goto unlock_out;
lock_page(new_page);
ret = __replace_page(vma, old_page, new_page);
ret = __replace_page(vma, vaddr, old_page, new_page);
unlock_page(new_page);
unlock_out: