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KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of unaligned size

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If a memory slot's size is not a multiple of 64 pages (256K), then
the KVM_CLEAR_DIRTY_LOG API is unusable: clearing the final 64 pages
either requires the requested page range to go beyond memslot->npages,
or requires log->num_pages to be unaligned, and kvm_clear_dirty_log_protect
requires log->num_pages to be both in range and aligned.

To allow this case, allow log->num_pages not to be a multiple of 64 if
it ends exactly on the last page of the slot.

Reported-by: Peter Xu <peterx@redhat.com>
Fixes: 98938aa8ed ("KVM: validate userspace input in kvm_clear_dirty_log_protect()", 2019-01-02)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2019-04-17 15:28:44 +02:00
parent 0699c64a4b
commit 76d58e0f07
3 changed files with 13 additions and 8 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

5
Documentation/virtual/kvm/api.txt
View file

@ -3830,8 +3830,9 @@ The ioctl clears the dirty status of pages in a memory slot, according to
the bitmap that is passed in struct kvm_clear_dirty_log's dirty_bitmap the bitmap that is passed in struct kvm_clear_dirty_log's dirty_bitmap
field. Bit 0 of the bitmap corresponds to page "first_page" in the field. Bit 0 of the bitmap corresponds to page "first_page" in the
memory slot, and num_pages is the size in bits of the input bitmap. memory slot, and num_pages is the size in bits of the input bitmap.
Both first_page and num_pages must be a multiple of 64. For each bit first_page must be a multiple of 64; num_pages must also be a multiple of
that is set in the input bitmap, the corresponding page is marked "clean" 64 unless first_page + num_pages is the size of the memory slot. For each
bit that is set in the input bitmap, the corresponding page is marked "clean"
in KVM's dirty bitmap, and dirty tracking is re-enabled for that page in KVM's dirty bitmap, and dirty tracking is re-enabled for that page
(for example via write-protection, or by clearing the dirty bit in (for example via write-protection, or by clearing the dirty bit in
a page table entry). a page table entry).

9
tools/testing/selftests/kvm/dirty_log_test.c
View file

@ -288,8 +288,11 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
#endif #endif
max_gfn = (1ul << (guest_pa_bits - guest_page_shift)) - 1; max_gfn = (1ul << (guest_pa_bits - guest_page_shift)) - 1;
guest_page_size = (1ul << guest_page_shift); guest_page_size = (1ul << guest_page_shift);
/* 1G of guest page sized pages */ /*
guest_num_pages = (1ul << (30 - guest_page_shift)); * A little more than 1G of guest page sized pages. Cover the
* case where the size is not aligned to 64 pages.
*/
guest_num_pages = (1ul << (30 - guest_page_shift)) + 3;
host_page_size = getpagesize(); host_page_size = getpagesize();
host_num_pages = (guest_num_pages * guest_page_size) / host_page_size + host_num_pages = (guest_num_pages * guest_page_size) / host_page_size +
!!((guest_num_pages * guest_page_size) % host_page_size); !!((guest_num_pages * guest_page_size) % host_page_size);
@ -359,7 +362,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
kvm_vm_get_dirty_log(vm, TEST_MEM_SLOT_INDEX, bmap); kvm_vm_get_dirty_log(vm, TEST_MEM_SLOT_INDEX, bmap);
#ifdef USE_CLEAR_DIRTY_LOG #ifdef USE_CLEAR_DIRTY_LOG
kvm_vm_clear_dirty_log(vm, TEST_MEM_SLOT_INDEX, bmap, 0, kvm_vm_clear_dirty_log(vm, TEST_MEM_SLOT_INDEX, bmap, 0,
DIV_ROUND_UP(host_num_pages, 64) * 64); host_num_pages);
#endif #endif
vm_dirty_log_verify(bmap); vm_dirty_log_verify(bmap);
iteration++; iteration++;

5
virt/kvm/kvm_main.c
View file

@ -1240,7 +1240,7 @@ int kvm_clear_dirty_log_protect(struct kvm *kvm,
if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS) if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS)
return -EINVAL; return -EINVAL;
if ((log->first_page & 63) || (log->num_pages & 63)) if (log->first_page & 63)
return -EINVAL; return -EINVAL;
slots = __kvm_memslots(kvm, as_id); slots = __kvm_memslots(kvm, as_id);
@ -1253,7 +1253,8 @@ int kvm_clear_dirty_log_protect(struct kvm *kvm,
n = kvm_dirty_bitmap_bytes(memslot); n = kvm_dirty_bitmap_bytes(memslot);
if (log->first_page > memslot->npages || if (log->first_page > memslot->npages ||
log->num_pages > memslot->npages - log->first_page) log->num_pages > memslot->npages - log->first_page ||
(log->num_pages < memslot->npages - log->first_page && (log->num_pages & 63)))
return -EINVAL; return -EINVAL;
*flush = false; *flush = false;