Commit 65c4189d authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of unaligned size 



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: default avatarPeter Xu <peterx@redhat.com>
Fixes: 98938aa8 ("KVM: validate userspace input in kvm_clear_dirty_log_protect()", 2019-01-02)
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0967fa1c

Documentation/virtual/kvm/api.txt

+3 −2
Original line number Diff line number Diff line
@@ -3812,8 +3812,9 @@ 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).

tools/testing/selftests/kvm/dirty_log_test.c

+2 −2
Original line number Diff line number Diff line
@@ -289,7 +289,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations, 
	max_gfn = (1ul << (guest_pa_bits - guest_page_shift)) - 1;

	guest_page_size = (1ul << guest_page_shift);

	/* 1G of guest page sized pages */

	guest_num_pages = (1ul << (30 - guest_page_shift));

	guest_num_pages = (1ul << (30 - guest_page_shift)) + 3;

	host_page_size = getpagesize();

	host_num_pages = (guest_num_pages * guest_page_size) / host_page_size +

			 !!((guest_num_pages * guest_page_size) % host_page_size);
@@ -359,7 +359,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations, 
		kvm_vm_get_dirty_log(vm, TEST_MEM_SLOT_INDEX, bmap);

#ifdef USE_CLEAR_DIRTY_LOG

		kvm_vm_clear_dirty_log(vm, TEST_MEM_SLOT_INDEX, bmap, 0,

				       DIV_ROUND_UP(host_num_pages, 64) * 64);

				       host_num_pages);

#endif

		vm_dirty_log_verify(bmap);

		iteration++;

virt/kvm/kvm_main.c

+4 −3
Original line number Diff line number Diff line
@@ -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)

		return -EINVAL;



	if ((log->first_page & 63) || (log->num_pages & 63))

	if (log->first_page & 63)

		return -EINVAL;



	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);



	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;



	*flush = false;

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