Hello.
It is not clear to me if Linus still dislikes this change or not.
Let me send the patch "officially" so that it can be nacked if I
misunderstood the result of discussion.
Changes:
- add a huge comment above gup(WRITE | FORCE)
- add WARN_ON(!(PageAnon() && page_mapcount() == 1))
to ensure it works as expected
If (say, on x86) we can avoid the pte games, we can simply add
if (IS_ENABLED(CONFIG_WHATEVER)) {
copy_to_page(...);
set_page_dirty_locked(page);
goto put;
}
right after the 2nd get_user_pages().
In any case I believe it would be very nice to kill __replace_page(),
and even the fact this patch removes include(mm/internal.h) makes me
think this patch makes sense. Assuming it is correct.
Oleg.
---
int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,
uprobe_opcode_t opcode)
{
struct page *page;
struct vm_area_struct *vma;
pte_t *ptep, entry;
spinlock_t *ptlp;
int ret;
/* Read the page with vaddr into memory */
ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
if (ret < 0)
return ret;
ret = verify_opcode(page, vaddr, &opcode);
if (ret <= 0)
goto put;
retry:
put_page(page);
/*
* Break the mapping unless the page is already anonymous and
* unshare the page, see the WARN_ON() below.
*
* We never write to the VM_SHARED vma, every caller must check
* valid_vma(). FOLL_WRITE | FOLL_FORCE should anonymize this
* page unless uprobe_write_opcode() was already called in the
* past or the application itself did mprotect(PROT_WRITE) and
* wrote into this page.
*
* If it was already anonymous it can be shared due to dup_mm(),
* in this case do_wp_page() or do_swap_page() will do another
* cow to unshare, so we can safely modify it.
*/
ret = get_user_pages(NULL, mm, vaddr, 1, 1, 1, &page, &vma);
if (ret < 0)
return ret;
ptep = page_check_address(page, mm, vaddr, &ptlp, 0);
if (!ptep)
goto retry;
ret = 0;
if (WARN_ON(!PageAnon(page) || page_mapcount(page) != 1)) {
dump_page(page);
ret = -EFAULT;
goto unlock;
}
/* Unmap this page to ensure that nobody can execute it */
flush_cache_page(vma, vaddr, pte_pfn(*ptep));
entry = ptep_clear_flush(vma, vaddr, ptep);
/* Nobody can fault in this page, modify it */
copy_to_page(page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
/* Restore the old mapping */
entry = pte_mkdirty(entry);
flush_icache_page(vma, page);
set_pte_at(mm, vaddr, ptep, entry);
update_mmu_cache(vma, vaddr, ptep);
unlock:
pte_unmap_unlock(ptep, ptlp);
put:
put_page(page);
return ret;
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
