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[35.230.65.123]) by smtp.gmail.com with ESMTPSA id e2-20020a17090a118200b001ef3f85d1aasm5821172pja.9.2022.07.15.07.47.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 Jul 2022 07:47:40 -0700 (PDT) Date: Fri, 15 Jul 2022 14:47:36 +0000 From: Sean Christopherson To: Yu Zhang Cc: pbonzini@redhat.com, vkuznets@redhat.com, jmattson@google.com, joro@8bytes.org, wanpengli@tencent.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] KVM: X86: Initialize 'fault' in kvm_fixup_and_inject_pf_error(). Message-ID: References: <20220715114211.53175-1-yu.c.zhang@linux.intel.com> <20220715114211.53175-2-yu.c.zhang@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220715114211.53175-2-yu.c.zhang@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, Jul 15, 2022, Yu Zhang wrote: > kvm_fixup_and_inject_pf_error() was introduced to fixup the error code( > e.g., to add RSVD flag) and inject the #PF to the guest, when guest > MAXPHYADDR is smaller than the host one. > > When it comes to nested, L0 is expected to intercept and fix up the #PF > and then inject to L2 directly if > - L2.MAXPHYADDR < L0.MAXPHYADDR and > - L1 has no intention to intercept L2's #PF (e.g., L2 and L1 have the > same MAXPHYADDR value && L1 is using EPT for L2), > instead of constructing a #PF VM Exit to L1. Currently, with PFEC_MASK > and PFEC_MATCH both set to 0 in vmcs02, the interception and injection > may happen on all L2 #PFs. > > However, failing to initialize 'fault' in kvm_fixup_and_inject_pf_error() > may cause the fault.async_page_fault being NOT zeroed, and later the #PF > being treated as a nested async page fault, and then being injected to L1. > So just fix it by initialize the 'fault' value in the beginning. Ouch. > Fixes: 897861479c064 ("KVM: x86: Add helper functions for illegal GPA checking and page fault injection") > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216178 > Reported-by: Yang Lixiao > Signed-off-by: Yu Zhang > --- > 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 031678eff28e..3246b3c9dfb3 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -12983,7 +12983,7 @@ EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value); > void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_code) > { > struct kvm_mmu *mmu = vcpu->arch.walk_mmu; > - struct x86_exception fault; > + struct x86_exception fault = {0}; > u64 access = error_code & > (PFERR_WRITE_MASK | PFERR_FETCH_MASK | PFERR_USER_MASK); As stupid as it may be to intentionally not fix the uninitialized data in a robust way, I'd actually prefer to manually clear fault.async_page_fault instead of zero-initializing the struct. Unlike a similar bug fix in commit 159e037d2e36 ("KVM: x86: Fully initialize 'struct kvm_lapic_irq' in kvm_pv_kick_cpu_op()"), this code actually cares about async_page_fault being false as opposed to just being _initialized_. And if another field is added to struct x86_exception in the future, leaving the struct uninitialized means that if such a patch were to miss this case, running with various sanitizers should in theory be able to detect such a bug. I suspect no one has found this with syzkaller due to the need to opt into running with allow_smaller_maxphyaddr=1. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index f389691d8c04..aeed737b55c2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12996,6 +12996,7 @@ void kvm_fixup_and_inject_pf_error(struct kvm_vcpu *vcpu, gva_t gva, u16 error_c fault.error_code = error_code; fault.nested_page_fault = false; fault.address = gva; + fault.async_page_fault = false; } vcpu->arch.walk_mmu->inject_page_fault(vcpu, &fault); }