From: Sean Christopherson seanjc@google.com
commit c87661f855c3f2023e40ddc364002601ee234367 upstream.
Fix a goof in kvm_prepare_memory_region() where KVM fails to free the new memslot's dirty bitmap during a CREATE action if kvm_arch_prepare_memory_region() fails. The logic is supposed to detect if the bitmap was allocated and thus needs to be freed, versus if the bitmap was inherited from the old memslot and thus needs to be kept. If there is no old memslot, then obviously the bitmap can't have been inherited
The bug was exposed by commit 86931ff7207b ("KVM: x86/mmu: Do not create SPTEs for GFNs that exceed host.MAXPHYADDR"), which made it trivally easy for syzkaller to trigger failure during kvm_arch_prepare_memory_region(), but the bug can be hit other ways too, e.g. due to -ENOMEM when allocating x86's memslot metadata.
The backtrace from kmemleak:
__vmalloc_node_range+0xb40/0xbd0 mm/vmalloc.c:3195 __vmalloc_node mm/vmalloc.c:3232 [inline] __vmalloc+0x49/0x50 mm/vmalloc.c:3246 __vmalloc_array mm/util.c:671 [inline] __vcalloc+0x49/0x70 mm/util.c:694 kvm_alloc_dirty_bitmap virt/kvm/kvm_main.c:1319 kvm_prepare_memory_region virt/kvm/kvm_main.c:1551 kvm_set_memslot+0x1bd/0x690 virt/kvm/kvm_main.c:1782 __kvm_set_memory_region+0x689/0x750 virt/kvm/kvm_main.c:1949 kvm_set_memory_region virt/kvm/kvm_main.c:1962 kvm_vm_ioctl_set_memory_region virt/kvm/kvm_main.c:1974 kvm_vm_ioctl+0x377/0x13a0 virt/kvm/kvm_main.c:4528 vfs_ioctl fs/ioctl.c:51 __do_sys_ioctl fs/ioctl.c:870 __se_sys_ioctl fs/ioctl.c:856 __x64_sys_ioctl+0xfc/0x140 fs/ioctl.c:856 do_syscall_x64 arch/x86/entry/common.c:50 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x44/0xae
And the relevant sequence of KVM events:
ioctl(3, KVM_CREATE_VM, 0) = 4 ioctl(4, KVM_SET_USER_MEMORY_REGION, {slot=0, flags=KVM_MEM_LOG_DIRTY_PAGES, guest_phys_addr=0x10000000000000, memory_size=4096, userspace_addr=0x20fe8000} ) = -1 EINVAL (Invalid argument)
Fixes: 244893fa2859 ("KVM: Dynamically allocate "new" memslots from the get-go") Cc: stable@vger.kernel.org Reported-by: syzbot+8606b8a9cc97a63f1c87@syzkaller.appspotmail.com Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20220518003842.1341782-1-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- virt/kvm/kvm_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1539,7 +1539,7 @@ static int kvm_prepare_memory_region(str r = kvm_arch_prepare_memory_region(kvm, old, new, change);
/* Free the bitmap on failure if it was allocated above. */ - if (r && new && new->dirty_bitmap && old && !old->dirty_bitmap) + if (r && new && new->dirty_bitmap && (!old || !old->dirty_bitmap)) kvm_destroy_dirty_bitmap(new);
return r;