* Tianyu Lan <lantianyu1986@xxxxxxxxx> wrote: > Hi Jim&Wanpeng: > Thanks for your help. > > 2017-12-08 5:25 GMT+08:00 Jim Mattson <jmattson@xxxxxxxxxx>: > > Try disabling the module parameter, "unrestricted_guest." Make sure > > that the module parameter, "emulate_invalid_guest_state" is enabled. > > This combination allows userspace to feed invalid guest state into the > > in-kernel emulator. > > Yes, you are right. I need to disable unrestricted_guest to reproduce the issue. > > I find this is pop instruction emulation issue. According "SDM VOL2, > chapter INSTRUCTION > SET REFERENCE. POP—Pop a Value from the Stack" > > Protected Mode Exceptions > #GP(0) If attempt is made to load SS register with NULL segment selector. > > This test case hits it but current code doesn't check such case. > The following patch can fix the issue. > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index abe74f7..e2ac5cc 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -1844,6 +1844,9 @@ static int emulate_pop(struct x86_emulate_ctxt *ctxt, > int rc; > struct segmented_address addr; > > + if ( !get_segment_selector(ctxt, VCPU_SREG_SS)) > + return emulate_gp(ctxt, 0); > + > addr.ea = reg_read(ctxt, VCPU_REGS_RSP) & stack_mask(ctxt); > addr.seg = VCPU_SREG_SS; > rc = segmented_read(ctxt, addr, dest, len); s/if ( !get_segment_selector /if (!get_segment_selector I think it would also be nice to convert the syzkaller testcase to a new KVM unit test: git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git There's a test_pop() function in kvm-unit-tests/x86/emulator.c. Thanks, Ingo
