Messages in this thread |  | | Date | Wed, 22 Nov 2017 11:43:03 +0200 | From | Liran Alon <> | Subject | Re: [PATCH] KVM: VMX: Fix vmx->nested freeing when no SMI handler |
| |
On 22/11/17 11:31, Wanpeng Li wrote: > 2017-11-22 17:07 GMT+08:00 Liran Alon <LIRAN.ALON@oracle.com>: >> >> >> On 22/11/17 10:45, Liran Alon wrote: >>> >>> >>> >>> On 22/11/17 09:56, Wanpeng Li wrote: >>>> >>>> From: Wanpeng Li <wanpeng.li@hotmail.com> >>>> >>>> Reported by syzkaller: >>>> >>>> ------------[ cut here ]------------ >>>> WARNING: CPU: 5 PID: 2939 at arch/x86/kvm/vmx.c:3844 >>>> free_loaded_vmcs+0x77/0x80 [kvm_intel] >>>> CPU: 5 PID: 2939 Comm: repro Not tainted 4.14.0+ #26 >>>> RIP: 0010:free_loaded_vmcs+0x77/0x80 [kvm_intel] >>>> Call Trace: >>>> vmx_free_vcpu+0xda/0x130 [kvm_intel] >>>> kvm_arch_destroy_vm+0x192/0x290 [kvm] >>>> kvm_put_kvm+0x262/0x560 [kvm] >>>> kvm_vm_release+0x2c/0x30 [kvm] >>>> __fput+0x190/0x370 >>>> task_work_run+0xa1/0xd0 >>>> do_exit+0x4d2/0x13e0 >>>> do_group_exit+0x89/0x140 >>>> get_signal+0x318/0xb80 >>>> do_signal+0x8c/0xb40 >>>> exit_to_usermode_loop+0xe4/0x140 >>>> syscall_return_slowpath+0x206/0x230 >>>> entry_SYSCALL_64_fastpath+0x98/0x9a >>>> >>>> The syzkaller testcase will execute VMXON/VMLAUCH instructions, so the >>>> vmx->nested stuff is populated, it will also issue KVM_SMI ioctl. >>>> However, >>>> the testcase is just a simple c program and not be lauched by something >>>> like seabios which implements smi_handler. Commit 05cade71cf (KVM: nSVM: >>>> fix SMI injection in guest mode) gets out of guest mode and set >>>> nested.vmxon >>>> to false for the duration of SMM according to SDM 34.14.1 "leave VMX >>>> operation" upon entering SMM. We can't alloc/free the vmx->nested stuff >>>> each time when entering/exiting SMM since it will induce more >>>> overhead. So >>>> the function vmx_pre_enter_smm() marks nested.vmxon false even if >>>> vmx->nested >>>> stuff is still populated. What it expected is em_rsm() can mark >>>> nested.vmxon >>>> to be true again. However, the smi_handler/rsm will not execute since >>>> there >>>> is no something like seabios in this scenario. The function free_nested() >>>> fails to free the vmx->nested stuff since the vmx->nested.vmxon is false >>>> which results in the above warning. >>>> >>>> This patch fixes it by also considering the no SMI handler case, luckily >>>> vmx->nested.smm.vmxon is marked according to the value of >>>> vmx->nested.vmxon >>>> in vmx_pre_enter_smm(), we can take advantage of it and free vmx->nested >>>> stuff when L1 goes down. >>>> >>>> Reported-by: Dmitry Vyukov <dvyukov@google.com> >>>> Cc: Paolo Bonzini <pbonzini@redhat.com> >>>> Cc: Radim Krčmář <rkrcmar@redhat.com> >>>> Cc: Dmitry Vyukov <dvyukov@google.com> >>>> Fixes: 05cade71cf (KVM: nSVM: fix SMI injection in guest mode) >>>> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com> >>>> --- >>>> arch/x86/kvm/vmx.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >>>> index dccc0f7..ed22425 100644 >>>> --- a/arch/x86/kvm/vmx.c >>>> +++ b/arch/x86/kvm/vmx.c >>>> @@ -7372,7 +7372,7 @@ static inline void nested_release_vmcs12(struct >>>> vcpu_vmx *vmx) >>>> */ >>>> static void free_nested(struct vcpu_vmx *vmx) >>>> { >>>> - if (!vmx->nested.vmxon) >>>> + if (!vmx->nested.vmxon && !vmx->nested.smm.vmxon) >>>> return; >>>> >>>> vmx->nested.vmxon = false; >>>> >>> Funny bug. Great analysis. >>> Reviewed-by: Liran Alon <liran.alon@oracle.com> >> >> Actually, I would add one more thing to patch: >> I think we should also set "vmx->nested.smm.vmxon = false;" after >> "vmx->nested.vmxon = false;" to correctlyhandle the case VMXOFF is executed >> from SMI handler. Otherwise, when SMI handler executes RSM, we will reach >> vmx_pre_leave_smm() which will set again "vmx->nested.vmxon = true;" which I >> think shouldn't happen. > > I didn't see a real scenario for this. Actually I later saw that handle_vmoff() calls nested_vmx_check_permission() which indeed won't allow to continue executing if running from SMI because vmx->nested.vmxon=false; and therefore this will raise a #UD. So you are right. :) > > Regards, > Wanpeng Li >
|  |