The only safe way for non core/arch code to use follow_pfn() is together with an mmu_notifier subscription. follow_pfn() is already marked as _GPL and the kerneldoc explains this restriction.
This patch here enforces all this by adding a mmu_notifier argument and verifying that it is registered for the correct mm_struct.
Motivated by discussions with Christoph Hellwig and Jason Gunthorpe.
Since requiring an mmu_notifier makes it very clear that follow_pfn() cannot be used on !CONFIG_MMU hardware, remove it from there. The sole user kvm not existing on such hardware also supports that.
Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Christoph Hellwig hch@infradead.org Cc: Jason Gunthorpe jgg@ziepe.ca Cc: Kees Cook keescook@chromium.org Cc: Dan Williams dan.j.williams@intel.com Cc: Andrew Morton akpm@linux-foundation.org Cc: John Hubbard jhubbard@nvidia.com Cc: Jérôme Glisse jglisse@redhat.com Cc: Jan Kara jack@suse.cz Cc: Dan Williams dan.j.williams@intel.com Cc: linux-mm@kvack.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-samsung-soc@vger.kernel.org Cc: linux-media@vger.kernel.org Cc: kvm@vger.kernel.org Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch -- v7: Comments from Jason: - ditch follow_pfn from nommu.c - simplify mmu_notifer->mm check --- include/linux/mm.h | 3 ++- mm/memory.c | 38 ++++++++++++++++++++++++-------------- mm/nommu.c | 27 +++++---------------------- virt/kvm/kvm_main.c | 4 ++-- 4 files changed, 33 insertions(+), 39 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index bb3e926afd91..2a564bfd818c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1651,6 +1651,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct vm_area_struct *start_vma, unsigned long start, unsigned long end);
struct mmu_notifier_range; +struct mmu_notifier;
void free_pgd_range(struct mmu_gather *tlb, unsigned long addr, unsigned long end, unsigned long floor, unsigned long ceiling); @@ -1660,7 +1661,7 @@ int follow_pte_pmd(struct mm_struct *mm, unsigned long address, struct mmu_notifier_range *range, pte_t **ptepp, pmd_t **pmdpp, spinlock_t **ptlp); int follow_pfn(struct vm_area_struct *vma, unsigned long address, - unsigned long *pfn); + unsigned long *pfn, struct mmu_notifier *subscription); int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, unsigned long *pfn); int follow_phys(struct vm_area_struct *vma, unsigned long address, diff --git a/mm/memory.c b/mm/memory.c index 0db0c5e233fd..a27b9b9c22c2 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -4789,11 +4789,30 @@ int follow_pte_pmd(struct mm_struct *mm, unsigned long address, } EXPORT_SYMBOL(follow_pte_pmd);
+static int __follow_pfn(struct vm_area_struct *vma, unsigned long address, + unsigned long *pfn) +{ + int ret = -EINVAL; + spinlock_t *ptl; + pte_t *ptep; + + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) + return ret; + + ret = follow_pte(vma->vm_mm, address, &ptep, &ptl); + if (ret) + return ret; + *pfn = pte_pfn(*ptep); + pte_unmap_unlock(ptep, ptl); + return 0; +} + /** * follow_pfn - look up PFN at a user virtual address * @vma: memory mapping * @address: user virtual address * @pfn: location to store found PFN + * @subscription: mmu_notifier subscription for the mm @vma is part of * * Only IO mappings and raw PFN mappings are allowed. Note that callers must * ensure coherency with pte updates by using a &mmu_notifier to follow updates. @@ -4805,21 +4824,12 @@ EXPORT_SYMBOL(follow_pte_pmd); * Return: zero and the pfn at @pfn on success, -ve otherwise. */ int follow_pfn(struct vm_area_struct *vma, unsigned long address, - unsigned long *pfn) + unsigned long *pfn, struct mmu_notifier *subscription) { - int ret = -EINVAL; - spinlock_t *ptl; - pte_t *ptep; - - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) - return ret; + if (WARN_ON(subscription->mm != vma->vm_mm)) + return -EINVAL;
- ret = follow_pte(vma->vm_mm, address, &ptep, &ptl); - if (ret) - return ret; - *pfn = pte_pfn(*ptep); - pte_unmap_unlock(ptep, ptl); - return 0; + return __follow_pfn(vma, address, pfn); } EXPORT_SYMBOL_GPL(follow_pfn);
@@ -4844,7 +4854,7 @@ int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, WARN_ONCE(1, "unsafe follow_pfn usage\n"); add_taint(TAINT_USER, LOCKDEP_STILL_OK);
- return follow_pfn(vma, address, pfn); + return __follow_pfn(vma, address, pfn); } EXPORT_SYMBOL(unsafe_follow_pfn);
diff --git a/mm/nommu.c b/mm/nommu.c index 79fc98a6c94a..a1e178401146 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -111,27 +111,6 @@ unsigned int kobjsize(const void *objp) return page_size(page); }
-/** - * follow_pfn - look up PFN at a user virtual address - * @vma: memory mapping - * @address: user virtual address - * @pfn: location to store found PFN - * - * Only IO mappings and raw PFN mappings are allowed. - * - * Returns zero and the pfn at @pfn on success, -ve otherwise. - */ -int follow_pfn(struct vm_area_struct *vma, unsigned long address, - unsigned long *pfn) -{ - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) - return -EINVAL; - - *pfn = address >> PAGE_SHIFT; - return 0; -} -EXPORT_SYMBOL_GPL(follow_pfn); - /** * unsafe_follow_pfn - look up PFN at a user virtual address * @vma: memory mapping @@ -153,7 +132,11 @@ int unsafe_follow_pfn(struct vm_area_struct *vma, unsigned long address, WARN_ONCE(1, "unsafe follow_pfn usage\n"); add_taint(TAINT_USER, LOCKDEP_STILL_OK);
- return follow_pfn(vma, address, pfn); + if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) + return -EINVAL; + + *pfn = address >> PAGE_SHIFT; + return 0; } EXPORT_SYMBOL(unsafe_follow_pfn);
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 417f3d470c3e..6f6786524eff 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1891,7 +1891,7 @@ static int hva_to_pfn_remapped(struct kvm *kvm, struct vm_area_struct *vma, unsigned long pfn; int r;
- r = follow_pfn(vma, addr, &pfn); + r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier); if (r) { /* * get_user_pages fails for VM_IO and VM_PFNMAP vmas and does @@ -1906,7 +1906,7 @@ static int hva_to_pfn_remapped(struct kvm *kvm, struct vm_area_struct *vma, if (r) return r;
- r = follow_pfn(vma, addr, &pfn); + r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier); if (r) return r;