Subject: Re: Coverity: handle_vmclear(): Error handling issues

From: Sean Christopherson <[email-masked]>
Date: Thu, 1 Dec 2022 18:26:57 +0000

On Thu, Dec 01, 2022, coverity-bot wrote:
> Hello!
> 
> This is an experimental semi-automated report about issues detected by
> Coverity from a scan of next-20221201 as part of the linux-next scan project:
> https://scan.coverity.com/projects/linux-next-weekly-scan
> 
> You're getting this email because you were associated with the identified
> lines of code (noted below) that were touched by commits:
> 
>   Fri Dec 14 17:59:46 2018 +0100
>     55d2375e58a6 ("KVM: nVMX: Move nested code to dedicated files")
> 
> Coverity reported the following:
> 
> *** CID 1527765:  Error handling issues  (CHECKED_RETURN)
> arch/x86/kvm/vmx/nested.c:5269 in handle_vmclear()
> 5263     	 */
> 5264     	if (likely(!guest_cpuid_has_evmcs(vcpu) ||
> 5265     		   !evmptr_is_valid(nested_get_evmptr(vcpu)))) {
> 5266     		if (vmptr == vmx->nested.current_vmptr)
> 5267     			nested_release_vmcs12(vcpu);
> 5268
> vvv     CID 1527765:  Error handling issues  (CHECKED_RETURN)
> vvv     Calling "kvm_vcpu_write_guest" without checking return value (as is done elsewhere 7 out of 8 times).
> 5269     		kvm_vcpu_write_guest(vcpu,
> 5270     				     vmptr + offsetof(struct vmcs12,
> 5271     						      launch_state),
> 5272     				     &zero, sizeof(zero));

Good bot.  Some day we'll hopefully do more than freak out if writing guest memory
fails, so I think we want this:

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index b28be793de29..938900c0c994 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5266,10 +5266,12 @@ static int handle_vmclear(struct kvm_vcpu *vcpu)
                if (vmptr == vmx->nested.current_vmptr)
                        nested_release_vmcs12(vcpu);
 
-               kvm_vcpu_write_guest(vcpu,
-                                    vmptr + offsetof(struct vmcs12,
-                                                     launch_state),
-                                    &zero, sizeof(zero));
+               r = kvm_vcpu_write_guest(vcpu,
+                                        vmptr + offsetof(struct vmcs12,
+                                                         launch_state),
+                                        &zero, sizeof(zero));
+               if (r)
+                       return kvm_handle_memory_failure(vcpu, r, NULL);
        } else if (vmx->nested.hv_evmcs && vmptr == vmx->nested.hv_evmcs_vmptr) {
                nested_release_evmcs(vcpu);
        }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7f850dfb4086..8f720107b77c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -13123,6 +13123,9 @@ int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
                              struct x86_exception *e)
 {
        if (r == X86EMUL_PROPAGATE_FAULT) {
+               if (KVM_BUG_ON(!e, vcpu->kvm))
+                       return -EIO;
+
                kvm_inject_emulated_page_fault(vcpu, e);
                return 1;
        }