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mm/mprotect: drop pgprot_t parameter from change_protection()

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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: David 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
David Hildenbrand 2022-12-23 16:56:16 +01:00 committed by Andrew Morton
parent 931298e103
commit 1ef488edd6
4 changed files with 18 additions and 9 deletions
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3
include/linux/mm.h
View file

@ -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);

3
mm/mempolicy.c
View file

@ -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);

18
mm/mprotect.c
View file

@ -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

3
mm/userfaultfd.c
View file

@ -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);
}