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Commit c517ee74 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
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uprobes: __replace_page() should not use page_address_in_vma() 



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: default avatarOleg 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: default avatarIngo Molnar <mingo@kernel.org>
parent f403072c

kernel/events/uprobes.c

+4 −7
Original line number Diff line number Diff line
@@ -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: