Messages in this thread Patch in this message |  | | Date | Sat, 24 Dec 2022 18:01:15 +0100 | Subject | Re: [PATCH v1 2/2] mm/mprotect: drop pgprot_t parameter from change_protection() | From | David Hildenbrand <> |
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On 23.12.22 16:56, David Hildenbrand wrote: > 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. > > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > include/linux/mm.h | 3 +-- > mm/mempolicy.c | 3 +-- > mm/mprotect.c | 14 +++++++++++--- > mm/userfaultfd.c | 3 +-- > 4 files changed, 14 insertions(+), 9 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f3f196e4d66d..b8be8c33ca20 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2148,8 +2148,7 @@ 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); > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > index 61aa9aedb728..c3f02703a710 100644 > --- a/mm/mempolicy.c > +++ b/mm/mempolicy.c > @@ -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); > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index 908df12caa26..569cefa668a6 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -503,13 +503,21 @@ 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); > > + /* > + * 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; > + > if (is_vm_hugetlb_page(vma)) > pages = hugetlb_change_protection(vma, start, end, newprot, > cp_flags); > @@ -638,7 +646,7 @@ 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 > diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c > index 351e8d6b398b..be7ee9d82e72 100644 > --- a/mm/userfaultfd.c > +++ b/mm/userfaultfd.c > @@ -744,8 +744,7 @@ void uffd_wp_range(struct mm_struct *dst_mm, struct vm_area_struct *dst_vma, > if (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); > } >
The following fix for compilation errors without PAGE_NONE:
From a164d6cf728e353294aa9e65b8ead5241c800421 Mon Sep 17 00:00:00 2001 From: David Hildenbrand <david@redhat.com> Date: Sat, 24 Dec 2022 15:01:18 +0100 Subject: [PATCH] fixup: mm/mprotect: drop pgprot_t parameter from change_protection()
PAGE_NONE might not be defined without CONFIG_NUMA_BALANCING
Signed-off-by: David Hildenbrand <david@redhat.com> --- mm/mprotect.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/mprotect.c b/mm/mprotect.c index 569cefa668a6..809832954898 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -510,6 +510,7 @@ unsigned long change_protection(struct mmu_gather *tlb, 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 @@ -517,6 +518,9 @@ unsigned long change_protection(struct mmu_gather *tlb, */ 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, -- 2.38.1
-- Thanks,
David / dhildenb
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