From mboxrd@z Thu Jan 1 00:00:00 1970 From: Liran Alon Subject: Re: [PATCH] KVM: VMX: Fix vmx->nested freeing when no SMI handler Date: Wed, 22 Nov 2017 11:07:39 +0200 Message-ID: <5A153E5B.2060104@ORACLE.COM> References: <1511337410-8100-1-git-send-email-wanpeng.li@hotmail.com> <5A153926.7030004@ORACLE.COM> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Dmitry Vyukov To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <5A153926.7030004@ORACLE.COM> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 22/11/17 10:45, Liran Alon wrote: > > > On 22/11/17 09:56, Wanpeng Li wrote: >> From: Wanpeng Li >> >> 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 >> Cc: Paolo Bonzini >> Cc: Radim Krčmář >> Cc: Dmitry Vyukov >> Fixes: 05cade71cf (KVM: nSVM: fix SMI injection in guest mode) >> Signed-off-by: Wanpeng Li >> --- >> 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 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. Regards, -Liran