From a2b0ce3c22062da7e8657d8e9b72be32c6e9d848 Mon Sep 17 00:00:00 2001 From: Felipe Franciosi Date: Tue, 19 May 2020 08:11:22 +0000 Subject: [PATCH] KVM: x86: respect singlestep when emulating instruction commit 384dea1c9183880be183cfaae161d99aafd16df6 upstream. When userspace configures KVM_GUESTDBG_SINGLESTEP, KVM will manage the presence of X86_EFLAGS_TF via kvm_set/get_rflags on vcpus. The actual rflag bit is therefore hidden from callers. That includes init_emulate_ctxt() which uses the value returned from kvm_get_flags() to set ctxt->tf. As a result, x86_emulate_instruction() will skip a single step, leaving singlestep_rip stale and not returning to userspace. This resolves the issue by observing the vcpu guest_debug configuration alongside ctxt->tf in x86_emulate_instruction(), performing the single step if set. Cc: stable@vger.kernel.org Signed-off-by: Felipe Franciosi Message-Id: <20200519081048.8204-1-felipe@nutanix.com> Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/x86.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index c6d9e363dfc0..8c21976e86b7 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6833,7 +6833,7 @@ restart: if (!ctxt->have_exception || exception_type(ctxt->exception.vector) == EXCPT_TRAP) { kvm_rip_write(vcpu, ctxt->eip); - if (r && ctxt->tf) + if (r && (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP))) r = kvm_vcpu_do_singlestep(vcpu); __kvm_set_rflags(vcpu, ctxt->eflags); }