• Wanpeng Li's avatar
    KVM: Fix stack-out-of-bounds read in write_mmio · e39d200f
    Wanpeng Li authored
    Reported by syzkaller:
    
      BUG: KASAN: stack-out-of-bounds in write_mmio+0x11e/0x270 [kvm]
      Read of size 8 at addr ffff8803259df7f8 by task syz-executor/32298
    
      CPU: 6 PID: 32298 Comm: syz-executor Tainted: G           OE    4.15.0-rc2+ #18
      Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS FBKTC1AUS 02/16/2016
      Call Trace:
       dump_stack+0xab/0xe1
       print_address_description+0x6b/0x290
       kasan_report+0x28a/0x370
       write_mmio+0x11e/0x270 [kvm]
       emulator_read_write_onepage+0x311/0x600 [kvm]
       emulator_read_write+0xef/0x240 [kvm]
       emulator_fix_hypercall+0x105/0x150 [kvm]
       em_hypercall+0x2b/0x80 [kvm]
       x86_emulate_insn+0x2b1/0x1640 [kvm]
       x86_emulate_instruction+0x39a/0xb90 [kvm]
       handle_exception+0x1b4/0x4d0 [kvm_intel]
       vcpu_enter_guest+0x15a0/0x2640 [kvm]
       kvm_arch_vcpu_ioctl_run+0x549/0x7d0 [kvm]
       kvm_vcpu_ioctl+0x479/0x880 [kvm]
       do_vfs_ioctl+0x142/0x9a0
       SyS_ioctl+0x74/0x80
       entry_SYSCALL_64_fastpath+0x23/0x9a
    
    The path of patched vmmcall will patch 3 bytes opcode 0F 01 C1(vmcall)
    to the guest memory, however, write_mmio tracepoint always prints 8 bytes
    through *(u64 *)val since kvm splits the mmio access into 8 bytes. This
    leaks 5 bytes from the kernel stack (CVE-2017-17741).  This patch fixes
    it by just accessing the bytes which we operate on.
    
    Before patch:
    
    syz-executor-5567  [007] .... 51370.561696: kvm_mmio: mmio write len 3 gpa 0x10 val 0x1ffff10077c1010f
    
    After patch:
    
    syz-executor-13416 [002] .... 51302.299573: kvm_mmio: mmio write len 3 gpa 0x10 val 0xc1010f
    Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
    Reviewed-by: default avatarDarren Kenny <darren.kenny@oracle.com>
    Reviewed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Tested-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Radim Krčmář <rkrcmar@redhat.com>
    Cc: Marc Zyngier <marc.zyngier@arm.com>
    Cc: Christoffer Dall <christoffer.dall@linaro.org>
    Signed-off-by: default avatarWanpeng Li <wanpeng.li@hotmail.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    e39d200f
x86.c 228 KB