• Wanpeng Li's avatar
    KVM: mmu: Fix overlap between public and private memslots · b28676bb
    Wanpeng Li authored
    Reported by syzkaller:
    
        pte_list_remove: ffff9714eb1f8078 0->BUG
        ------------[ cut here ]------------
        kernel BUG at arch/x86/kvm/mmu.c:1157!
        invalid opcode: 0000 [#1] SMP
        RIP: 0010:pte_list_remove+0x11b/0x120 [kvm]
        Call Trace:
         drop_spte+0x83/0xb0 [kvm]
         mmu_page_zap_pte+0xcc/0xe0 [kvm]
         kvm_mmu_prepare_zap_page+0x81/0x4a0 [kvm]
         kvm_mmu_invalidate_zap_all_pages+0x159/0x220 [kvm]
         kvm_arch_flush_shadow_all+0xe/0x10 [kvm]
         kvm_mmu_notifier_release+0x6c/0xa0 [kvm]
         ? kvm_mmu_notifier_release+0x5/0xa0 [kvm]
         __mmu_notifier_release+0x79/0x110
         ? __mmu_notifier_release+0x5/0x110
         exit_mmap+0x15a/0x170
         ? do_exit+0x281/0xcb0
         mmput+0x66/0x160
         do_exit+0x2c9/0xcb0
         ? __context_tracking_exit.part.5+0x4a/0x150
         do_group_exit+0x50/0xd0
         SyS_exit_group+0x14/0x20
         do_syscall_64+0x73/0x1f0
         entry_SYSCALL64_slow_path+0x25/0x25
    
    The reason is that when creates new memslot, there is no guarantee for new
    memslot not overlap with private memslots. This can be triggered by the
    following program:
    
       #include <fcntl.h>
       #include <pthread.h>
       #include <setjmp.h>
       #include <signal.h>
       #include <stddef.h>
       #include <stdint.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>
       #include <sys/ioctl.h>
       #include <sys/stat.h>
       #include <sys/syscall.h>
       #include <sys/types.h>
       #include <unistd.h>
       #include <linux/kvm.h>
    
       long r[16];
    
       int main()
       {
    	void *p = valloc(0x4000);
    
    	r[2] = open("/dev/kvm", 0);
    	r[3] = ioctl(r[2], KVM_CREATE_VM, 0x0ul);
    
    	uint64_t addr = 0xf000;
    	ioctl(r[3], KVM_SET_IDENTITY_MAP_ADDR, &addr);
    	r[6] = ioctl(r[3], KVM_CREATE_VCPU, 0x0ul);
    	ioctl(r[3], KVM_SET_TSS_ADDR, 0x0ul);
    	ioctl(r[6], KVM_RUN, 0);
    	ioctl(r[6], KVM_RUN, 0);
    
    	struct kvm_userspace_memory_region mr = {
    		.slot = 0,
    		.flags = KVM_MEM_LOG_DIRTY_PAGES,
    		.guest_phys_addr = 0xf000,
    		.memory_size = 0x4000,
    		.userspace_addr = (uintptr_t) p
    	};
    	ioctl(r[3], KVM_SET_USER_MEMORY_REGION, &mr);
    	return 0;
       }
    
    This patch fixes the bug by not adding a new memslot even if it
    overlaps with private memslots.
    Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Radim Krčmář <rkrcmar@redhat.com>
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Eric Biggers <ebiggers3@gmail.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarWanpeng Li <wanpeng.li@hotmail.com>
    ---
     virt/kvm/kvm_main.c | 3 +--
     1 file changed, 1 insertion(+), 2 deletions(-)
    b28676bb
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