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[146.148.121.110]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-498010aade3sm84008685e9.14.2026.07.30.11.24.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2026 11:24:33 -0700 (PDT) From: Dmytro Maluka To: Sean Christopherson Cc: Paolo Bonzini , Dave Hansen , Mathias Krause , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Vineeth Pillai , Chuanxiao Dong , Aashish Sharma , Grzegorz Jaszczyk , Dmytro Maluka Subject: [PATCH 2/3] KVM: x86: Fix off-by-one in max_vcpu_ids bounds checks Date: Thu, 30 Jul 2026 18:24:24 +0000 Message-ID: <20260730182425.1223530-3-dmaluka@chromium.org> X-Mailer: git-send-email 2.55.0.508.g3f0d502094-goog In-Reply-To: <20260730182425.1223530-1-dmaluka@chromium.org> References: <20260730182425.1223530-1-dmaluka@chromium.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit max_vcpu_ids and KVM_CAP_MAX_VCPU_ID are exclusive, i.e. the maximum allowed vcpu_id value is max_vcpu_ids minus one, not max_vcpu_ids. Fix sanity checks for KVM_SET_BOOT_CPU_ID and KVM_CAP_MAX_VCPU_ID to fail when bsp_vcpu_id is incorrectly set to max_vcpu_ids, not to a value below max_vcpu_ids. Fixes: 7c305d5118e6 ("KVM: x86: Limit check IDs for KVM_SET_BOOT_CPU_ID") Fixes: d29bf2ca1404 ("KVM: x86: Prevent excluding the BSP on setting max_vcpu_ids") Signed-off-by: Dmytro Maluka --- arch/x86/kvm/x86.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 47cb9eba113b..b576b46869d2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6908,7 +6908,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, break; mutex_lock(&kvm->lock); - if (kvm->arch.bsp_vcpu_id > cap->args[0]) { + if (kvm->arch.bsp_vcpu_id >= cap->args[0]) { ; } else if (kvm->arch.max_vcpu_ids == cap->args[0]) { r = 0; @@ -7478,8 +7478,8 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg) mutex_lock(&kvm->lock); if (kvm->created_vcpus) r = -EBUSY; - else if (arg > KVM_MAX_VCPU_IDS || - (kvm->arch.max_vcpu_ids && arg > kvm->arch.max_vcpu_ids)) + else if (arg >= KVM_MAX_VCPU_IDS || + (kvm->arch.max_vcpu_ids && arg >= kvm->arch.max_vcpu_ids)) r = -EINVAL; else kvm->arch.bsp_vcpu_id = arg; -- 2.55.0.508.g3f0d502094-goog