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AJvYcCXqDmgC2H9I9oxUQcUoz4eYrjHuXUi70IhGqHS1KRt05F9Sd2c+G4GlyBMbyF94weOVeoDdnwUp5doJiDHV/7DeoInK X-Gm-Message-State: AOJu0Yy1o7ADIXk6aVdMJtmiaXbhpkH3Be5AYokAPpv+nebb3lxi6lep dWP66Xq6nOaXoj55A5Hwke+3SBG1ATrEiTZ1dlRWYyUpZJpP7EFFqJCrJIlwthRVTaa1weh+k/N ZICD84bhwhw== X-Google-Smtp-Source: AGHT+IFV8XW0q6Vc+/y+/ULmmUgE0pK+amRiYPmJG0lNXqT19q15J8nIrLHDkebqo9zBkflGqNFe7OG5YJeiaQ== X-Received: from dmatlack-n2d-128.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:1309]) (user=dmatlack job=sendgmr) by 2002:a05:6902:1023:b0:dd9:1db5:8348 with SMTP id x3-20020a056902102300b00dd91db58348mr1087385ybt.8.1714760260354; Fri, 03 May 2024 11:17:40 -0700 (PDT) Date: Fri, 3 May 2024 11:17:32 -0700 In-Reply-To: <20240503181734.1467938-1-dmatlack@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240503181734.1467938-1-dmatlack@google.com> X-Mailer: git-send-email 2.45.0.rc1.225.g2a3ae87e7f-goog Message-ID: <20240503181734.1467938-2-dmatlack@google.com> Subject: [PATCH v3 1/3] KVM: Introduce vcpu->wants_to_run From: David Matlack To: Paolo Bonzini Cc: Marc Zyngier , Oliver Upton , James Morse , Suzuki K Poulose , Zenghui Yu , Tianrui Zhao , Bibo Mao , Huacai Chen , Michael Ellerman , Nicholas Piggin , Anup Patel , Atish Patra , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , David Hildenbrand , Sean Christopherson , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, David Matlack Introduce vcpu->wants_to_run to indicate when a vCPU is in its core run loop, i.e. when the vCPU is running the KVM_RUN ioctl and immediate_exit was not set. Replace all references to vcpu->run->immediate_exit with !vcpu->wants_to_run to avoid TOCTOU races with userspace. For example, a malicious userspace could invoked KVM_RUN with immediate_exit=true and then after KVM reads it to set wants_to_run=false, flip it to false. This would result in the vCPU running in KVM_RUN with wants_to_run=false. This wouldn't cause any real bugs today but is a dangerous landmine. Signed-off-by: David Matlack --- arch/arm64/kvm/arm.c | 2 +- arch/loongarch/kvm/vcpu.c | 2 +- arch/mips/kvm/mips.c | 2 +- arch/powerpc/kvm/powerpc.c | 2 +- arch/riscv/kvm/vcpu.c | 2 +- arch/s390/kvm/kvm-s390.c | 2 +- arch/x86/kvm/x86.c | 4 ++-- include/linux/kvm_host.h | 1 + virt/kvm/kvm_main.c | 3 +++ 9 files changed, 12 insertions(+), 8 deletions(-) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index c4a0a35e02c7..c587e5d9396e 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -986,7 +986,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) vcpu_load(vcpu); - if (run->immediate_exit) { + if (!vcpu->wants_to_run) { ret = -EINTR; goto out; } diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c index 3a8779065f73..847ef54f3a84 100644 --- a/arch/loongarch/kvm/vcpu.c +++ b/arch/loongarch/kvm/vcpu.c @@ -1163,7 +1163,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_complete_iocsr_read(vcpu, run); } - if (run->immediate_exit) + if (!vcpu->wants_to_run) return r; /* Clear exit_reason */ diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c index 231ac052b506..f1a99962027a 100644 --- a/arch/mips/kvm/mips.c +++ b/arch/mips/kvm/mips.c @@ -436,7 +436,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) vcpu->mmio_needed = 0; } - if (vcpu->run->immediate_exit) + if (!vcpu->wants_to_run) goto out; lose_fpu(1); diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c index d32abe7fe6ab..961aadc71de2 100644 --- a/arch/powerpc/kvm/powerpc.c +++ b/arch/powerpc/kvm/powerpc.c @@ -1852,7 +1852,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_sigset_activate(vcpu); - if (run->immediate_exit) + if (!vcpu->wants_to_run) r = -EINTR; else r = kvmppc_vcpu_run(vcpu); diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c index b5ca9f2e98ac..3d8349470ee6 100644 --- a/arch/riscv/kvm/vcpu.c +++ b/arch/riscv/kvm/vcpu.c @@ -711,7 +711,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) return ret; } - if (run->immediate_exit) { + if (!vcpu->wants_to_run) { kvm_vcpu_srcu_read_unlock(vcpu); return -EINTR; } diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index 5147b943a864..b1ea25aacbf9 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -5033,7 +5033,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) if (vcpu->kvm->arch.pv.dumping) return -EINVAL; - if (kvm_run->immediate_exit) + if (!vcpu->wants_to_run) return -EINTR; if (kvm_run->kvm_valid_regs & ~KVM_SYNC_S390_VALID_FIELDS || diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2d2619d3eee4..f70ae1558684 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11396,7 +11396,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) kvm_vcpu_srcu_read_lock(vcpu); if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) { - if (kvm_run->immediate_exit) { + if (!vcpu->wants_to_run) { r = -EINTR; goto out; } @@ -11474,7 +11474,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) WARN_ON_ONCE(vcpu->mmio_needed); } - if (kvm_run->immediate_exit) { + if (!vcpu->wants_to_run) { r = -EINTR; goto out; } diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index afbc99264ffa..f9b9ce0c3cd9 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -380,6 +380,7 @@ struct kvm_vcpu { bool dy_eligible; } spin_loop; #endif + bool wants_to_run; bool preempted; bool ready; struct kvm_vcpu_arch arch; diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 38b498669ef9..bdea5b978f80 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4425,7 +4425,10 @@ static long kvm_vcpu_ioctl(struct file *filp, synchronize_rcu(); put_pid(oldpid); } + vcpu->wants_to_run = !READ_ONCE(vcpu->run->immediate_exit); r = kvm_arch_vcpu_ioctl_run(vcpu); + vcpu->wants_to_run = false; + trace_kvm_userspace_exit(vcpu->run->exit_reason, r); break; }