Commit 1ef488ed authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/mprotect: drop pgprot_t parameter from change_protection() 

Being able to provide a custom protection opens the door for
inconsistencies and BUGs: for example, accidentally allowing for more
permissions than desired by other mechanisms (e.g., softdirty tracking). 
vma->vm_page_prot should be the single source of truth.

Only PROT_NUMA is special: there is no way we can erroneously allow
for more permissions when removing all permissions. Special-case using
the MM_CP_PROT_NUMA flag.

[david@redhat.com: PAGE_NONE might not be defined without CONFIG_NUMA_BALANCING]  
  Link: https://lkml.kernel.org/r/5084ff1c-ebb3-f918-6a60-bacabf550a88@redhat.com
Link: https://lkml.kernel.org/r/20221223155616.297723-3-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 931298e1

include/linux/mm.h

+1 −2
Original line number Diff line number Diff line
@@ -2134,8 +2134,7 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, 
			     pte_t pte);

extern unsigned long change_protection(struct mmu_gather *tlb,

			      struct vm_area_struct *vma, unsigned long start,

			      unsigned long end, pgprot_t newprot,

			      unsigned long cp_flags);

			      unsigned long end, unsigned long cp_flags);

extern int mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma,

			  struct vm_area_struct **pprev, unsigned long start,

			  unsigned long end, unsigned long newflags);

mm/mempolicy.c

+1 −2
Original line number Diff line number Diff line
@@ -635,8 +635,7 @@ unsigned long change_prot_numa(struct vm_area_struct *vma, 


	tlb_gather_mmu(&tlb, vma->vm_mm);



	nr_updated = change_protection(&tlb, vma, addr, end, PAGE_NONE,

				       MM_CP_PROT_NUMA);

	nr_updated = change_protection(&tlb, vma, addr, end, MM_CP_PROT_NUMA);

	if (nr_updated)

		count_vm_numa_events(NUMA_PTE_UPDATES, nr_updated);

mm/mprotect.c

+15 −3
Original line number Diff line number Diff line
@@ -507,13 +507,25 @@ static unsigned long change_protection_range(struct mmu_gather *tlb, 


unsigned long change_protection(struct mmu_gather *tlb,

		       struct vm_area_struct *vma, unsigned long start,

		       unsigned long end, pgprot_t newprot,

		       unsigned long cp_flags)

		       unsigned long end, unsigned long cp_flags)

{

	pgprot_t newprot = vma->vm_page_prot;

	unsigned long pages;



	BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL);



#ifdef CONFIG_NUMA_BALANCING

	/*

	 * Ordinary protection updates (mprotect, uffd-wp, softdirty tracking)

	 * are expected to reflect their requirements via VMA flags such that

	 * vma_set_page_prot() will adjust vma->vm_page_prot accordingly.

	 */

	if (cp_flags & MM_CP_PROT_NUMA)

		newprot = PAGE_NONE;

#else

	WARN_ON_ONCE(cp_flags & MM_CP_PROT_NUMA);

#endif



	if (is_vm_hugetlb_page(vma))

		pages = hugetlb_change_protection(vma, start, end, newprot,

						  cp_flags);
@@ -642,7 +654,7 @@ mprotect_fixup(struct mmu_gather *tlb, struct vm_area_struct *vma, 
		mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;

	vma_set_page_prot(vma);



	change_protection(tlb, vma, start, end, vma->vm_page_prot, mm_cp_flags);

	change_protection(tlb, vma, start, end, mm_cp_flags);



	/*

	 * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major

mm/userfaultfd.c

+1 −2
Original line number Diff line number Diff line
@@ -730,8 +730,7 @@ void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma, 
	if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma))

		mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;

	tlb_gather_mmu(&tlb, dst_mm);

	change_protection(&tlb, dst_vma, start, start + len, vma->vm_page_prot,

			  mm_cp_flags);

	change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags);

	tlb_finish_mmu(&tlb);

}