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AL+hErFUxqsucpd4jszLnrBoGbsfz2WcMD8yyQ/CqsaiGGzVR1KjwSiscgEXnYIpQMij9Qevz+4fgGB0AaaJaCY=@vger.kernel.org X-Gm-Message-State: APuU4Z8HkTxj2A18bm796dMe+nr1HI7IWz9LM80b8ZEeD65jB3YzOlLe fgJkkLWqdAQD1jcVDSmetXUNORxxeVPfpFC6VX82qslTjVqhLy0SMqG4H0zfUYqHUPOZI+Ufe3M XCWS7QKTw8R8xLg== X-Received: from ilbdw15-n1.prod.google.com ([2002:a05:6e02:410f:10b0:51a:346:d73b]) (user=jmattson job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6808:c168:b0:4d6:90f4:48b7 with SMTP id 5614622812f47-56b986255cbmr3796223b6e.57.1794442124402; Wed, 11 Nov 2026 16:08:44 -0800 (PST) Date: Wed, 11 Nov 2026 16:08:41 -0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 X-Mailer: git-send-email 2.56.0.567.gdb80ae8cd5-goog Message-ID: <20261112000841.3013324-1-jmattson@google.com> Subject: [PATCH v2] KVM: nSVM: Add missing CET VMRUN consistency checks From: Jim Mattson To: Sean Christopherson , Paolo Bonzini Cc: Yosry Ahmed , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jim Mattson Content-Type: text/plain; charset="UTF-8" Per the APM, "Canonicalization and Consistency Checks," [t]he following conditions are considered illegal state combinations: - CR4.CET=1 when CR0.WP=0 - Any reserved bit set in S_CET - CR4.CET=1 and U_CET.SS=1 when EFLAGS.VM=1 Check these conditions in software before trying to VMRUN vmcb02, so that the illegal states result in a #VMEXIT to L1 rather than an exit to userspace with KVM_EXIT_FAIL_ENTRY. Fixes: c5ba49458513 ("KVM: nSVM: Save/load CET Shadow Stack state to/from vmcb12/vmcb02") Signed-off-by: Jim Mattson --- v1 -> v2: - Warn and fail VMRUN if reading MSR_IA32_U_CET fails [Yosry] v1: https://lore.kernel.org/all/20261110004037.125692-1-jmattson@google.com/ arch/x86/kvm/svm/nested.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index af0ef678433d..6298160458bc 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -469,6 +469,21 @@ static bool nested_vmcb_check_save(struct kvm_vcpu *vcpu, if (CC(!__kvm_is_valid_cr4(vcpu, save->cr4))) return false; + if (CC((save->cr4 & X86_CR4_CET) && !(save->cr0 & X86_CR0_WP))) + return false; + + if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) && + CC(!kvm_is_valid_u_s_cet(vcpu, save->s_cet))) + return false; + + if ((save->cr4 & X86_CR4_CET) && (save->rflags & X86_EFLAGS_VM)) { + u64 u_cet = 0; + + if (WARN_ON_ONCE(__kvm_emulate_msr_read(vcpu, MSR_IA32_U_CET, &u_cet)) || + CC(u_cet & CET_SHSTK_EN)) + return false; + } + if (CC(!kvm_valid_efer(vcpu, save->efer))) return false; -- 2.56.0.567.gdb80ae8cd5-goog