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([2604:3d08:8e80:f800:3c86:745c:97f1:5486]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2eb39266f42sm384225ad.40.2026.10.29.16.50.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2026 16:50:45 -0700 (PDT) From: ma.mandourr@gmail.com To: Sean Christopherson , Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Mahmoud Abumandour Subject: [PATCH 1/2] KVM: nVMX: Don't let L2's LMSW modify CR0 bits owned by L1 Date: Thu, 29 Oct 2026 16:50:39 -0700 Message-ID: <20261029235040.12013-2-ma.mandourr@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20261029235040.12013-1-ma.mandourr@gmail.com> References: <20261029235040.12013-1-ma.mandourr@gmail.com> 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 Content-Transfer-Encoding: 8bit From: Mahmoud Abumandour When L2's LMSW exits to L0 but not to L1, emulate it through handle_set_cr0(), as is done for MOV to CR0. kvm_lmsw() ignores vmcs12's CR0 guest/host mask, so L2 could change CR0 bits that L1 owns, e.g. clear TS, and read their effective values instead of the read shadow. Fixes: eeadf9e7558c ("KVM: nVMX: Handling of CR0 and CR4 modifying instructions") Signed-off-by: Mahmoud Abumandour --- arch/x86/kvm/vmx/vmx.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index b341af4c60..3633496299 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -5748,6 +5748,21 @@ static int handle_cr(struct kvm_vcpu *vcpu) case 3: /* lmsw */ val = (exit_qualification >> LMSW_SOURCE_DATA_SHIFT) & 0x0f; trace_kvm_cr_write(0, (kvm_read_cr0_bits(vcpu, ~0xful) | val)); + if (is_guest_mode(vcpu)) { + struct vmcs12 *vmcs12 = get_vmcs12(vcpu); + unsigned long mask = vmcs12->cr0_guest_host_mask; + unsigned long cr0; + + /* + * LMSW leaves the bits L1 owns unmodified, as does a MOV + * to CR0 that writes their read shadow values. Emulate + * it as that MOV: L2's view of CR0 with LMSW's bits. + */ + cr0 = (kvm_read_cr0(vcpu) & ~mask) | + (vmcs12->cr0_read_shadow & mask); + err = handle_set_cr0(vcpu, (cr0 & ~0x0eul) | val); + return kvm_complete_insn_gp(vcpu, err); + } kvm_lmsw(vcpu, val); return kvm_skip_emulated_instruction(vcpu); -- 2.25.1