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Subject[PATCH] KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of unaligned size
Date
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: 98938aa8edd6 ("KVM: validate userspace input in kvm_clear_dirty_log_protect()", 2019-01-02)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
Documentation/virtual/kvm/api.txt | 5 +++--
tools/testing/selftests/kvm/dirty_log_test.c | 4 ++--
virt/kvm/kvm_main.c | 7 ++++---
3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index b62ad0d94234..de97369ad30d 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3829,8 +3829,9 @@ 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).
diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 4715cfba20dc..052fb5856df4 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -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++;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f4da53321161..ace23d8a309f 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1269,7 +1269,7 @@ 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);
@@ -1282,8 +1282,9 @@ 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);
--
1.8.3.1
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