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![Mel Gorman](/assets/img/avatar_default.png)
Nadav Amit identified a theoritical race between page reclaim and mprotect due to TLB flushes being batched outside of the PTL being held. He described the race as follows: CPU0 CPU1 ---- ---- user accesses memory using RW PTE [PTE now cached in TLB] try_to_unmap_one() ==> ptep_get_and_clear() ==> set_tlb_ubc_flush_pending() mprotect(addr, PROT_READ) ==> change_pte_range() ==> [ PTE non-present - no flush ] user writes using cached RW PTE ... try_to_unmap_flush() The same type of race exists for reads when protecting for PROT_NONE and also exists for operations that can leave an old TLB entry behind such as munmap, mremap and madvise. For some operations like mprotect, it's not necessarily a data integrity issue but it is a correctness issue as there is a window where an mprotect that limits access still allows access. For munmap, it's potentially a data integrity issue although the race is massive as an munmap, mmap and return to userspace must all complete between the window when reclaim drops the PTL and flushes the TLB. However, it's theoritically possible so handle this issue by flushing the mm if reclaim is potentially currently batching TLB flushes. Other instances where a flush is required for a present pte should be ok as either the page lock is held preventing parallel reclaim or a page reference count is elevated preventing a parallel free leading to corruption. In the case of page_mkclean there isn't an obvious path that userspace could take advantage of without using the operations that are guarded by this patch. Other users such as gup as a race with reclaim looks just at PTEs. huge page variants should be ok as they don't race with reclaim. mincore only looks at PTEs. userfault also should be ok as if a parallel reclaim takes place, it will either fault the page back in or read some of the data before the flush occurs triggering a fault. Note that a variant of this patch was acked by Andy Lutomirski but this was for the x86 parts on top of his PCID work which didn't make the 4.13 merge window as expected. His ack is dropped from this version and there will be a follow-on patch on top of PCID that will include his ack. [akpm@linux-foundation.org: tweak comments] [akpm@linux-foundation.org: fix spello] Link: http://lkml.kernel.org/r/20170717155523.emckq2esjro6hf3z@suse.de Reported-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Mel Gorman <mgorman@suse.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: <stable@vger.kernel.org> [v4.4+] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
556 lines
14 KiB
C
556 lines
14 KiB
C
/*
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* mm/mprotect.c
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*
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* (C) Copyright 1994 Linus Torvalds
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* (C) Copyright 2002 Christoph Hellwig
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*
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* Address space accounting code <alan@lxorguk.ukuu.org.uk>
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* (C) Copyright 2002 Red Hat Inc, All Rights Reserved
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*/
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#include <linux/mm.h>
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#include <linux/hugetlb.h>
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#include <linux/shm.h>
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#include <linux/mman.h>
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#include <linux/fs.h>
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#include <linux/highmem.h>
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#include <linux/security.h>
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#include <linux/mempolicy.h>
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#include <linux/personality.h>
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#include <linux/syscalls.h>
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#include <linux/swap.h>
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#include <linux/swapops.h>
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#include <linux/mmu_notifier.h>
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#include <linux/migrate.h>
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#include <linux/perf_event.h>
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#include <linux/pkeys.h>
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#include <linux/ksm.h>
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#include <linux/uaccess.h>
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#include <asm/pgtable.h>
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#include <asm/cacheflush.h>
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#include <asm/mmu_context.h>
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#include <asm/tlbflush.h>
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#include "internal.h"
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static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
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unsigned long addr, unsigned long end, pgprot_t newprot,
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int dirty_accountable, int prot_numa)
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{
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struct mm_struct *mm = vma->vm_mm;
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pte_t *pte, oldpte;
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spinlock_t *ptl;
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unsigned long pages = 0;
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int target_node = NUMA_NO_NODE;
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/*
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* Can be called with only the mmap_sem for reading by
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* prot_numa so we must check the pmd isn't constantly
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* changing from under us from pmd_none to pmd_trans_huge
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* and/or the other way around.
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*/
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if (pmd_trans_unstable(pmd))
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return 0;
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/*
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* The pmd points to a regular pte so the pmd can't change
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* from under us even if the mmap_sem is only hold for
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* reading.
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*/
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pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
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/* Get target node for single threaded private VMAs */
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if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
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atomic_read(&vma->vm_mm->mm_users) == 1)
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target_node = numa_node_id();
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flush_tlb_batched_pending(vma->vm_mm);
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arch_enter_lazy_mmu_mode();
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do {
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oldpte = *pte;
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if (pte_present(oldpte)) {
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pte_t ptent;
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bool preserve_write = prot_numa && pte_write(oldpte);
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/*
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* Avoid trapping faults against the zero or KSM
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* pages. See similar comment in change_huge_pmd.
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*/
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if (prot_numa) {
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struct page *page;
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page = vm_normal_page(vma, addr, oldpte);
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if (!page || PageKsm(page))
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continue;
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/* Avoid TLB flush if possible */
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if (pte_protnone(oldpte))
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continue;
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/*
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* Don't mess with PTEs if page is already on the node
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* a single-threaded process is running on.
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*/
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if (target_node == page_to_nid(page))
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continue;
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}
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ptent = ptep_modify_prot_start(mm, addr, pte);
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ptent = pte_modify(ptent, newprot);
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if (preserve_write)
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ptent = pte_mk_savedwrite(ptent);
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/* Avoid taking write faults for known dirty pages */
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if (dirty_accountable && pte_dirty(ptent) &&
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(pte_soft_dirty(ptent) ||
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!(vma->vm_flags & VM_SOFTDIRTY))) {
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ptent = pte_mkwrite(ptent);
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}
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ptep_modify_prot_commit(mm, addr, pte, ptent);
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pages++;
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} else if (IS_ENABLED(CONFIG_MIGRATION)) {
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swp_entry_t entry = pte_to_swp_entry(oldpte);
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if (is_write_migration_entry(entry)) {
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pte_t newpte;
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/*
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* A protection check is difficult so
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* just be safe and disable write
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*/
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make_migration_entry_read(&entry);
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newpte = swp_entry_to_pte(entry);
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if (pte_swp_soft_dirty(oldpte))
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newpte = pte_swp_mksoft_dirty(newpte);
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set_pte_at(mm, addr, pte, newpte);
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pages++;
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}
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}
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} while (pte++, addr += PAGE_SIZE, addr != end);
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arch_leave_lazy_mmu_mode();
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pte_unmap_unlock(pte - 1, ptl);
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return pages;
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}
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static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
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pud_t *pud, unsigned long addr, unsigned long end,
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pgprot_t newprot, int dirty_accountable, int prot_numa)
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{
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pmd_t *pmd;
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struct mm_struct *mm = vma->vm_mm;
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unsigned long next;
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unsigned long pages = 0;
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unsigned long nr_huge_updates = 0;
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unsigned long mni_start = 0;
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pmd = pmd_offset(pud, addr);
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do {
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unsigned long this_pages;
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next = pmd_addr_end(addr, end);
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if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
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&& pmd_none_or_clear_bad(pmd))
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continue;
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/* invoke the mmu notifier if the pmd is populated */
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if (!mni_start) {
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mni_start = addr;
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mmu_notifier_invalidate_range_start(mm, mni_start, end);
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}
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if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
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if (next - addr != HPAGE_PMD_SIZE) {
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__split_huge_pmd(vma, pmd, addr, false, NULL);
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} else {
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int nr_ptes = change_huge_pmd(vma, pmd, addr,
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newprot, prot_numa);
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if (nr_ptes) {
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if (nr_ptes == HPAGE_PMD_NR) {
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pages += HPAGE_PMD_NR;
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nr_huge_updates++;
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}
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/* huge pmd was handled */
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continue;
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}
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}
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/* fall through, the trans huge pmd just split */
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}
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this_pages = change_pte_range(vma, pmd, addr, next, newprot,
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dirty_accountable, prot_numa);
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pages += this_pages;
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} while (pmd++, addr = next, addr != end);
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if (mni_start)
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mmu_notifier_invalidate_range_end(mm, mni_start, end);
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if (nr_huge_updates)
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count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
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return pages;
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}
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static inline unsigned long change_pud_range(struct vm_area_struct *vma,
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p4d_t *p4d, unsigned long addr, unsigned long end,
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pgprot_t newprot, int dirty_accountable, int prot_numa)
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{
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pud_t *pud;
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unsigned long next;
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unsigned long pages = 0;
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pud = pud_offset(p4d, addr);
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do {
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next = pud_addr_end(addr, end);
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if (pud_none_or_clear_bad(pud))
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continue;
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pages += change_pmd_range(vma, pud, addr, next, newprot,
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dirty_accountable, prot_numa);
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} while (pud++, addr = next, addr != end);
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return pages;
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}
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static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
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pgd_t *pgd, unsigned long addr, unsigned long end,
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pgprot_t newprot, int dirty_accountable, int prot_numa)
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{
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p4d_t *p4d;
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unsigned long next;
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unsigned long pages = 0;
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p4d = p4d_offset(pgd, addr);
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do {
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next = p4d_addr_end(addr, end);
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if (p4d_none_or_clear_bad(p4d))
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continue;
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pages += change_pud_range(vma, p4d, addr, next, newprot,
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dirty_accountable, prot_numa);
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} while (p4d++, addr = next, addr != end);
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return pages;
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}
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static unsigned long change_protection_range(struct vm_area_struct *vma,
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unsigned long addr, unsigned long end, pgprot_t newprot,
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int dirty_accountable, int prot_numa)
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{
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struct mm_struct *mm = vma->vm_mm;
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pgd_t *pgd;
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unsigned long next;
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unsigned long start = addr;
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unsigned long pages = 0;
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BUG_ON(addr >= end);
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pgd = pgd_offset(mm, addr);
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flush_cache_range(vma, addr, end);
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set_tlb_flush_pending(mm);
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do {
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next = pgd_addr_end(addr, end);
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if (pgd_none_or_clear_bad(pgd))
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continue;
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pages += change_p4d_range(vma, pgd, addr, next, newprot,
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dirty_accountable, prot_numa);
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} while (pgd++, addr = next, addr != end);
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/* Only flush the TLB if we actually modified any entries: */
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if (pages)
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flush_tlb_range(vma, start, end);
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clear_tlb_flush_pending(mm);
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return pages;
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}
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unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
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unsigned long end, pgprot_t newprot,
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int dirty_accountable, int prot_numa)
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{
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unsigned long pages;
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if (is_vm_hugetlb_page(vma))
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pages = hugetlb_change_protection(vma, start, end, newprot);
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else
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pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
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return pages;
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}
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int
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mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
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unsigned long start, unsigned long end, unsigned long newflags)
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{
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struct mm_struct *mm = vma->vm_mm;
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unsigned long oldflags = vma->vm_flags;
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long nrpages = (end - start) >> PAGE_SHIFT;
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unsigned long charged = 0;
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pgoff_t pgoff;
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int error;
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int dirty_accountable = 0;
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if (newflags == oldflags) {
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*pprev = vma;
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return 0;
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}
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/*
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* If we make a private mapping writable we increase our commit;
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* but (without finer accounting) cannot reduce our commit if we
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* make it unwritable again. hugetlb mapping were accounted for
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* even if read-only so there is no need to account for them here
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*/
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if (newflags & VM_WRITE) {
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/* Check space limits when area turns into data. */
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if (!may_expand_vm(mm, newflags, nrpages) &&
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may_expand_vm(mm, oldflags, nrpages))
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return -ENOMEM;
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if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
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VM_SHARED|VM_NORESERVE))) {
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charged = nrpages;
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if (security_vm_enough_memory_mm(mm, charged))
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return -ENOMEM;
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newflags |= VM_ACCOUNT;
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}
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}
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/*
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* First try to merge with previous and/or next vma.
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*/
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pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
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*pprev = vma_merge(mm, *pprev, start, end, newflags,
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vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
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vma->vm_userfaultfd_ctx);
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if (*pprev) {
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vma = *pprev;
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VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
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goto success;
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}
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*pprev = vma;
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if (start != vma->vm_start) {
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error = split_vma(mm, vma, start, 1);
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if (error)
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goto fail;
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}
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if (end != vma->vm_end) {
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error = split_vma(mm, vma, end, 0);
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if (error)
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goto fail;
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}
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success:
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/*
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* vm_flags and vm_page_prot are protected by the mmap_sem
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* held in write mode.
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*/
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vma->vm_flags = newflags;
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dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
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vma_set_page_prot(vma);
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change_protection(vma, start, end, vma->vm_page_prot,
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dirty_accountable, 0);
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/*
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* Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
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* fault on access.
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*/
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if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
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(newflags & VM_WRITE)) {
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populate_vma_page_range(vma, start, end, NULL);
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}
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vm_stat_account(mm, oldflags, -nrpages);
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vm_stat_account(mm, newflags, nrpages);
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perf_event_mmap(vma);
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return 0;
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fail:
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vm_unacct_memory(charged);
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return error;
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}
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/*
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* pkey==-1 when doing a legacy mprotect()
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*/
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static int do_mprotect_pkey(unsigned long start, size_t len,
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unsigned long prot, int pkey)
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{
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unsigned long nstart, end, tmp, reqprot;
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struct vm_area_struct *vma, *prev;
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int error = -EINVAL;
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const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
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const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
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(prot & PROT_READ);
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prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
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if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
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return -EINVAL;
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if (start & ~PAGE_MASK)
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return -EINVAL;
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if (!len)
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return 0;
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len = PAGE_ALIGN(len);
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end = start + len;
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if (end <= start)
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return -ENOMEM;
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if (!arch_validate_prot(prot))
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return -EINVAL;
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reqprot = prot;
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if (down_write_killable(¤t->mm->mmap_sem))
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return -EINTR;
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/*
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* If userspace did not allocate the pkey, do not let
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* them use it here.
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*/
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error = -EINVAL;
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if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
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goto out;
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vma = find_vma(current->mm, start);
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error = -ENOMEM;
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if (!vma)
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goto out;
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prev = vma->vm_prev;
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if (unlikely(grows & PROT_GROWSDOWN)) {
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if (vma->vm_start >= end)
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goto out;
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start = vma->vm_start;
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error = -EINVAL;
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if (!(vma->vm_flags & VM_GROWSDOWN))
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goto out;
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} else {
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if (vma->vm_start > start)
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goto out;
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if (unlikely(grows & PROT_GROWSUP)) {
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end = vma->vm_end;
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error = -EINVAL;
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if (!(vma->vm_flags & VM_GROWSUP))
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goto out;
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}
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}
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if (start > vma->vm_start)
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prev = vma;
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for (nstart = start ; ; ) {
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unsigned long mask_off_old_flags;
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unsigned long newflags;
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int new_vma_pkey;
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/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
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/* Does the application expect PROT_READ to imply PROT_EXEC */
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if (rier && (vma->vm_flags & VM_MAYEXEC))
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prot |= PROT_EXEC;
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/*
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* Each mprotect() call explicitly passes r/w/x permissions.
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* If a permission is not passed to mprotect(), it must be
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* cleared from the VMA.
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*/
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mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
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ARCH_VM_PKEY_FLAGS;
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|
|
new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
|
|
newflags = calc_vm_prot_bits(prot, new_vma_pkey);
|
|
newflags |= (vma->vm_flags & ~mask_off_old_flags);
|
|
|
|
/* newflags >> 4 shift VM_MAY% in place of VM_% */
|
|
if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
|
|
error = -EACCES;
|
|
goto out;
|
|
}
|
|
|
|
error = security_file_mprotect(vma, reqprot, prot);
|
|
if (error)
|
|
goto out;
|
|
|
|
tmp = vma->vm_end;
|
|
if (tmp > end)
|
|
tmp = end;
|
|
error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
|
|
if (error)
|
|
goto out;
|
|
nstart = tmp;
|
|
|
|
if (nstart < prev->vm_end)
|
|
nstart = prev->vm_end;
|
|
if (nstart >= end)
|
|
goto out;
|
|
|
|
vma = prev->vm_next;
|
|
if (!vma || vma->vm_start != nstart) {
|
|
error = -ENOMEM;
|
|
goto out;
|
|
}
|
|
prot = reqprot;
|
|
}
|
|
out:
|
|
up_write(¤t->mm->mmap_sem);
|
|
return error;
|
|
}
|
|
|
|
SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
|
|
unsigned long, prot)
|
|
{
|
|
return do_mprotect_pkey(start, len, prot, -1);
|
|
}
|
|
|
|
#ifdef CONFIG_ARCH_HAS_PKEYS
|
|
|
|
SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
|
|
unsigned long, prot, int, pkey)
|
|
{
|
|
return do_mprotect_pkey(start, len, prot, pkey);
|
|
}
|
|
|
|
SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
|
|
{
|
|
int pkey;
|
|
int ret;
|
|
|
|
/* No flags supported yet. */
|
|
if (flags)
|
|
return -EINVAL;
|
|
/* check for unsupported init values */
|
|
if (init_val & ~PKEY_ACCESS_MASK)
|
|
return -EINVAL;
|
|
|
|
down_write(¤t->mm->mmap_sem);
|
|
pkey = mm_pkey_alloc(current->mm);
|
|
|
|
ret = -ENOSPC;
|
|
if (pkey == -1)
|
|
goto out;
|
|
|
|
ret = arch_set_user_pkey_access(current, pkey, init_val);
|
|
if (ret) {
|
|
mm_pkey_free(current->mm, pkey);
|
|
goto out;
|
|
}
|
|
ret = pkey;
|
|
out:
|
|
up_write(¤t->mm->mmap_sem);
|
|
return ret;
|
|
}
|
|
|
|
SYSCALL_DEFINE1(pkey_free, int, pkey)
|
|
{
|
|
int ret;
|
|
|
|
down_write(¤t->mm->mmap_sem);
|
|
ret = mm_pkey_free(current->mm, pkey);
|
|
up_write(¤t->mm->mmap_sem);
|
|
|
|
/*
|
|
* We could provie warnings or errors if any VMA still
|
|
* has the pkey set here.
|
|
*/
|
|
return ret;
|
|
}
|
|
|
|
#endif /* CONFIG_ARCH_HAS_PKEYS */
|