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AHgh+RrzpmVmXrmo1tP/FOW23Xxczy0VKn4dEboWN+m+2FlInYQ66jiUObyGBNRhRszb8tfG96M=@vger.kernel.org X-Gm-Message-State: AOJu0Yzg8OAYUsFRzqlCeF51n4wiX83MQEe6r89o+F8RK+n/noLMBKnV xDSouraV8Ple4f1gF2hcGKhIwC4YaI4P9Vm7hD82oGVFW48SehqTxVs64m3GBQbjuRjyv33Uykk ilku4Dg== X-Received: from plhi3.prod.google.com ([2002:a17:903:2ec3:b0:2cf:3e66:d26c]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:dac7:b0:2c7:ebfb:618f with SMTP id d9443c01a7336-2cfa6b73a76mr12595425ad.14.1784767049125; Wed, 22 Jul 2026 17:37:29 -0700 (PDT) Date: Wed, 22 Jul 2026 17:37:28 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260616004155.1435766-14-yosry@kernel.org> <20260616010534.2C8511F000E9@smtp.kernel.org> Message-ID: Subject: Re: [RFC PATCH v2 13/25] KVM: nSVM: Flush both L1 and L2 ASIDs on KVM_REQ_TLB_FLUSH From: Sean Christopherson To: Yosry Ahmed Cc: sashiko-reviews@lists.linux.dev, kvm@vger.kernel.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Tue, Jun 16, 2026, Yosry Ahmed wrote: > On Mon, Jun 15, 2026 at 6:05=E2=80=AFPM wrote: > > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > > > index dac3d0098bb77..4f13c3456a5d7 100644 > > > --- a/arch/x86/kvm/svm/svm.c > > > +++ b/arch/x86/kvm/svm/svm.c > > [ ... ] > > > @@ -4213,7 +4215,11 @@ static void svm_flush_tlb_all(struct kvm_vcpu = *vcpu) > > > if (WARN_ON_ONCE(svm_hv_is_enlightened_tlb_enabled(vcpu))) > > > hv_flush_remote_tlbs(vcpu->kvm); > > > > > > - svm_flush_tlb_asid(vcpu); > > > + kvm_hv_purge_all_tlb_flush_fifos(vcpu); > > > + > > > + vmcb_set_flush_asid(svm->vmcb01.ptr); > > > + if (svm->nested.vmcb02.ptr) > > > + vmcb_set_flush_asid(svm->nested.vmcb02.ptr); > > > > [Severity: High] > > Could this dereference of svm->nested.vmcb02.ptr cause a use-after-free= ? > > > > If svm_allocate_nested() successfully allocates vmcb02_page and assigns= it > > to svm->nested.vmcb02.ptr, but a subsequent allocation (such as msrpm) > > fails, the error path frees the page but does not clear the pointer: > > > > arch/x86/kvm/svm/nested.c:svm_allocate_nested() { > > ... > > err_free_vmcb02: > > __free_page(vmcb02_page); > > return -ENOMEM; > > } > > > > If a TLB flush is later triggered and calls svm_flush_tlb_all(), the ch= eck > > for if (svm->nested.vmcb02.ptr) would evaluate to true on the dangling > > pointer, and vmcb_set_flush_asid() would write to freed memory. > > > > Would it be safer to check svm->nested.initialized here instead, to ens= ure > > the nested state is fully allocated and valid? >=20 > Yes. But if no one objects, I'd rather add a patch to drop > svm->nested.initialized completely, and properly NULLify > svm->nested.vmcb02.ptr in the destruction paths. Keying off the > pointer makes more sense semantically imo. +1