From: Lai Jiangshan laijs@linux.alibaba.com
commit f85d40160691881a17a397c448d799dfc90987ba upstream.
When the host is using debug registers but the guest is not using them nor is the guest in guest-debug state, the kvm code does not reset the host debug registers before kvm_x86->run(). Rather, it relies on the hardware vmentry instruction to automatically reset the dr7 registers which ensures that the host breakpoints do not affect the guest.
This however violates the non-instrumentable nature around VM entry and exit; for example, when a host breakpoint is set on vcpu->arch.cr2,
Another issue is consistency. When the guest debug registers are active, the host breakpoints are reset before kvm_x86->run(). But when the guest debug registers are inactive, the host breakpoints are delayed to be disabled. The host tracing tools may see different results depending on what the guest is doing.
To fix the problems, we clear %db7 unconditionally before kvm_x86->run() if the host has set any breakpoints, no matter if the guest is using them or not.
Signed-off-by: Lai Jiangshan laijs@linux.alibaba.com Message-Id: 20210628172632.81029-1-jiangshanlai@gmail.com Cc: stable@vger.kernel.org [Only clear %db7 instead of reloading all debug registers. - Paolo] Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/x86.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9020,6 +9020,8 @@ static int vcpu_enter_guest(struct kvm_v set_debugreg(vcpu->arch.eff_db[3], 3); set_debugreg(vcpu->arch.dr6, 6); vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD; + } else if (unlikely(hw_breakpoint_active())) { + set_debugreg(0, 7); }
exit_fastpath = kvm_x86_ops.run(vcpu);