KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of unaligned size

mainline inclusion
from mainline-v5.1
commit: 76d58e0f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I66COX
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.10.y&id=76d58e0f07ec203bbdfcaabd9a9fc10a5a3ed5ea

--------------------------------

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: NPeter Xu <peterx@redhat.com>
Fixes: 98938aa8 ("KVM: validate userspace input in kvm_clear_dirty_log_protect()", 2019-01-02)
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
[Remove test code because the test code is too different.]
Signed-off-by: zhengchuan<zhengchuan@huawei.com>

Documentation/virtual/kvm/api.txt

@@ -3752,8 +3752,9 @@ 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
 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.
-Both first_page and num_pages must be a multiple of 64.  For each bit
-that is set in the input bitmap, the corresponding page is marked "clean"
+first_page must be a multiple of 64; num_pages must also be a multiple of
+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
 (for example via write-protection, or by clearing the dirty bit in
 a page table entry).

virt/kvm/kvm_main.c

@@ -1288,7 +1288,7 @@ int kvm_clear_dirty_log_protect(struct kvm *kvm,
 	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_USER_MEM_SLOTS)
 		return -EINVAL;
 
-	if ((log->first_page & 63) || (log->num_pages & 63))
+	if (log->first_page & 63)
 		return -EINVAL;
 
 	slots = __kvm_memslots(kvm, as_id);
@@ -1301,8 +1301,9 @@ int kvm_clear_dirty_log_protect(struct kvm *kvm,
 	n = kvm_dirty_bitmap_bytes(memslot);
 
 	if (log->first_page > memslot->npages ||
-	    log->num_pages > memslot->npages - log->first_page)
-			return -EINVAL;
+	    log->num_pages > memslot->npages - log->first_page ||
+	    (log->num_pages < memslot->npages - log->first_page && (log->num_pages & 63)))
+	    return -EINVAL;
 
 	*flush = false;
 	dirty_bitmap_buffer = kvm_second_dirty_bitmap(memslot);