From 8d5988f3eac1d0b5916ca6ff9191921a23a9ccd3 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Tue, 29 Jun 2021 01:26:32 +0800 Subject: [PATCH] KVM: X86: Disable hardware breakpoints unconditionally before kvm_x86->run() BugLink: https://bugs.launchpad.net/bugs/1939738 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 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 Signed-off-by: Greg Kroah-Hartman Signed-off-by: Kamal Mostafa Signed-off-by: Stefan Bader --- arch/x86/kvm/x86.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1497bbd02328..67258666b566 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9084,6 +9084,8 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) 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); -- 2.39.5