drivers/virt/acrn: fix PFNMAP PTE checks in acrn_vm_ram_map()

Patch series "mm: follow_pte() improvements and acrn follow_pte() fixes".

Patch #1 fixes a bunch of issues I spotted in the acrn driver.  It
compiles, that's all I know.  I'll appreciate some review and testing from
acrn folks.

Patch #2+#3 improve follow_pte(), passing a VMA instead of the MM, adding
more sanity checks, and improving the documentation.  Gave it a quick test
on x86-64 using VM_PAT that ends up using follow_pte().

This patch (of 3):

We currently miss handling various cases, resulting in a dangerous
follow_pte() (previously follow_pfn()) usage.

(1) We're not checking PTE write permissions.

Maybe we should simply always require pte_write() like we do for
pin_user_pages_fast(FOLL_WRITE)? Hard to tell, so let's check for
ACRN_MEM_ACCESS_WRITE for now.

(2) We're not rejecting refcounted pages.

As we are not using MMU notifiers, messing with refcounted pages is
dangerous and can result in use-after-free. Let's make sure to reject them.

(3) We are only looking at the first PTE of a bigger range.

We only lookup a single PTE, but memmap->len may span a larger area.
Let's loop over all involved PTEs and make sure the PFN range is
actually contiguous. Reject everything else: it couldn't have worked
either way, and rather made use access PFNs we shouldn't be accessing.

Link: https://lkml.kernel.org/r/20240410155527.474777-1-david@redhat.com
Link: https://lkml.kernel.org/r/20240410155527.474777-2-david@redhat.com
Fixes: 8a6e85f75a83 ("virt: acrn: obtain pa from VMA with PFNMAP flag")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Fei Li <fei1.li@intel.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Yonghua Huang <yonghua.huang@intel.com>
Cc: Sean Christopherson <seanjc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/drivers/virt/acrn/mm.c b/drivers/virt/acrn/mm.c
index b30077baf352b4e3aeb3881f936b61ef02e0d445..2d98e1e185c4773cbe030ea7c9d933d9e77f9097 100644 (file)
--- a/drivers/virt/acrn/mm.c
+++ b/drivers/virt/acrn/mm.c
@@ -156,23 +156,29 @@ int acrn_vm_memseg_unmap(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
 int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
 {
        struct vm_memory_region_batch *regions_info;
-       int nr_pages, i = 0, order, nr_regions = 0;
+       int nr_pages, i, order, nr_regions = 0;
        struct vm_memory_mapping *region_mapping;
        struct vm_memory_region_op *vm_region;
        struct page **pages = NULL, *page;
        void *remap_vaddr;
        int ret, pinned;
        u64 user_vm_pa;
-       unsigned long pfn;
        struct vm_area_struct *vma;
 
        if (!vm || !memmap)
                return -EINVAL;
 
+       /* Get the page number of the map region */
+       nr_pages = memmap->len >> PAGE_SHIFT;
+       if (!nr_pages)
+               return -EINVAL;
+
        mmap_read_lock(current->mm);
        vma = vma_lookup(current->mm, memmap->vma_base);
        if (vma && ((vma->vm_flags & VM_PFNMAP) != 0)) {
+               unsigned long start_pfn, cur_pfn;
                spinlock_t *ptl;
+               bool writable;
                pte_t *ptep;
 
                if ((memmap->vma_base + memmap->len) > vma->vm_end) {
@@ -180,25 +186,53 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
                        return -EINVAL;
                }
 
-               ret = follow_pte(vma->vm_mm, memmap->vma_base, &ptep, &ptl);
-               if (ret < 0) {
-                       mmap_read_unlock(current->mm);
+               for (i = 0; i < nr_pages; i++) {
+                       ret = follow_pte(vma->vm_mm,
+                                        memmap->vma_base + i * PAGE_SIZE,
+                                        &ptep, &ptl);
+                       if (ret)
+                               break;
+
+                       cur_pfn = pte_pfn(ptep_get(ptep));
+                       if (i == 0)
+                               start_pfn = cur_pfn;
+                       writable = !!pte_write(ptep_get(ptep));
+                       pte_unmap_unlock(ptep, ptl);
+
+                       /* Disallow write access if the PTE is not writable. */
+                       if (!writable &&
+                           (memmap->attr & ACRN_MEM_ACCESS_WRITE)) {
+                               ret = -EFAULT;
+                               break;
+                       }
+
+                       /* Disallow refcounted pages. */
+                       if (pfn_valid(cur_pfn) &&
+                           !PageReserved(pfn_to_page(cur_pfn))) {
+                               ret = -EFAULT;
+                               break;
+                       }
+
+                       /* Disallow non-contiguous ranges. */
+                       if (cur_pfn != start_pfn + i) {
+                               ret = -EINVAL;
+                               break;
+                       }
+               }
+               mmap_read_unlock(current->mm);
+
+               if (ret) {
                        dev_dbg(acrn_dev.this_device,
                                "Failed to lookup PFN at VMA:%pK.\n", (void *)memmap->vma_base);
                        return ret;
                }
-               pfn = pte_pfn(ptep_get(ptep));
-               pte_unmap_unlock(ptep, ptl);
-               mmap_read_unlock(current->mm);
 
                return acrn_mm_region_add(vm, memmap->user_vm_pa,
-                        PFN_PHYS(pfn), memmap->len,
+                        PFN_PHYS(start_pfn), memmap->len,
                         ACRN_MEM_TYPE_WB, memmap->attr);
        }
        mmap_read_unlock(current->mm);
 
-       /* Get the page number of the map region */
-       nr_pages = memmap->len >> PAGE_SHIFT;
        pages = vzalloc(array_size(nr_pages, sizeof(*pages)));
        if (!pages)
                return -ENOMEM;
@@ -242,12 +276,11 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
        mutex_unlock(&vm->regions_mapping_lock);
 
        /* Calculate count of vm_memory_region_op */
-       while (i < nr_pages) {
+       for (i = 0; i < nr_pages; i += 1 << order) {
                page = pages[i];
                VM_BUG_ON_PAGE(PageTail(page), page);
                order = compound_order(page);
                nr_regions++;
-               i += 1 << order;
        }
 
        /* Prepare the vm_memory_region_batch */
@@ -264,8 +297,7 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
        regions_info->vmid = vm->vmid;
        regions_info->regions_gpa = virt_to_phys(vm_region);
        user_vm_pa = memmap->user_vm_pa;
-       i = 0;
-       while (i < nr_pages) {
+       for (i = 0; i < nr_pages; i += 1 << order) {
                u32 region_size;
 
                page = pages[i];
@@ -281,7 +313,6 @@ int acrn_vm_ram_map(struct acrn_vm *vm, struct acrn_vm_memmap *memmap)
 
                vm_region++;
                user_vm_pa += region_size;
-               i += 1 << order;
        }
 
        /* Inform the ACRN Hypervisor to set up EPT mappings */