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    KVM: x86: fix singlestepping over syscall · c8401dda
    Paolo Bonzini 提交于
    TF is handled a bit differently for syscall and sysret, compared
    to the other instructions: TF is checked after the instruction completes,
    so that the OS can disable #DB at a syscall by adding TF to FMASK.
    When the sysret is executed the #DB is taken "as if" the syscall insn
    just completed.
    
    KVM emulates syscall so that it can trap 32-bit syscall on Intel processors.
    Fix the behavior, otherwise you could get #DB on a user stack which is not
    nice.  This does not affect Linux guests, as they use an IST or task gate
    for #DB.
    
    This fixes CVE-2017-7518.
    
    Cc: stable@vger.kernel.org
    Reported-by: NAndy Lutomirski <luto@kernel.org>
    Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>
    c8401dda
kvm_emulate.h 15.1 KB