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[104.155.91.135]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49e7d66ab6esm51074165e9.2.2026.09.15.00.34.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Sep 2026 00:34:51 -0700 (PDT) Date: Tue, 15 Sep 2026 08:34:48 +0100 From: Vincent Donnefort To: Fuad Tabba Cc: maz@kernel.org, oupton@kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, mark.rutland@arm.com, steven.price@arm.com, qperret@google.com, tabba@google.com Subject: Re: [PATCH v2 1/2] KVM: arm64: Validate the host vCPU's VM before reading it under pKVM Message-ID: References: <20260915070418.3209779-1-fuad.tabba@linux.dev> <20260915070418.3209779-2-fuad.tabba@linux.dev> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260915070418.3209779-2-fuad.tabba@linux.dev> On Tue, Sep 15, 2026 at 08:04:17AM +0100, Fuad Tabba wrote: > On an MTE-capable host under pKVM, enter_exception64() reads the VM's > MTE flag through vcpu->kvm, which for a host vCPU is a host-writable > pointer nothing validates. The host can point it at any address in the > hyp linear map and read back bit 1 of that word through PSR_TCO in the > vCPU's CPSR, or panic the hypervisor with an unmapped one. > > Get the VM through a get/put pair around the read: a loaded vCPU's is > the hyp VM, an unloaded host vCPU's is read once and pinned, and a > pointer the host never shared leaves TCO clear. > > Fixes: ea7fc1bb1cd1b ("KVM: arm64: Introduce MTE VM feature") > Reported-by: Sashiko > Closes: https://lore.kernel.org/all/20260914070536.877D91F000FF@smtp.kernel.org/ > Cc: stable@vger.kernel.org > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/hyp/exception.c | 5 ++- > arch/arm64/kvm/hyp/include/hyp/adjust_pc.h | 18 ++++++++++ > arch/arm64/kvm/hyp/nvhe/pkvm.c | 39 ++++++++++++++++++++++ > 3 files changed, 61 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c > index 754e2dc1df54a..6e60d890afa4a 100644 > --- a/arch/arm64/kvm/hyp/exception.c > +++ b/arch/arm64/kvm/hyp/exception.c > @@ -70,6 +70,7 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode, > enum exception_type type) > { > unsigned long sctlr, vbar, old, new, mode; > + struct kvm *kvm; > u64 exc_offset; > > mode = *vcpu_cpsr(vcpu) & (PSR_MODE_MASK | PSR_MODE32_BIT); > @@ -109,8 +110,10 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode, > new |= (old & PSR_C_BIT); > new |= (old & PSR_V_BIT); > > - if (kvm_has_mte(kern_hyp_va(vcpu->kvm))) > + kvm = vcpu_get_kvm(vcpu); > + if (kvm && kvm_has_mte(kvm)) > new |= PSR_TCO_BIT; > + vcpu_put_kvm(vcpu, kvm); > > new |= (old & PSR_DIT_BIT); > > diff --git a/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h b/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h > index 4fdfeabefeb43..a4fb04faa7d09 100644 > --- a/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h > +++ b/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h > @@ -13,6 +13,24 @@ > #include > #include > > +/* > + * Under pKVM a host vCPU's ->kvm is host-writable: the nVHE pair > + * validates it. > + */ > +#ifdef __KVM_NVHE_HYPERVISOR__ > +struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu); > +void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm); > +#else > +static inline struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu) > +{ > + return vcpu->kvm; > +} > + > +static inline void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm) > +{ > +} > +#endif > + > static inline void kvm_skip_instr(struct kvm_vcpu *vcpu) > { > if (vcpu_mode_is_32bit(vcpu)) { > diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c > index 459bd9eb7e4bc..9bdc7a9b84b8c 100644 > --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c > +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c > @@ -11,6 +11,8 @@ > > #include > > +#include > + > #include > #include > #include > @@ -304,6 +306,43 @@ struct pkvm_hyp_vcpu *pkvm_get_loaded_hyp_vcpu(void) > > } > > +static struct pkvm_hyp_vm *loaded_hyp_vm_of(struct kvm_vcpu *vcpu) pkvm_get_loaded_hyp_vm()? to align with the other. > +{ > + struct pkvm_hyp_vcpu *hyp_vcpu = pkvm_get_loaded_hyp_vcpu(); > + > + if (hyp_vcpu && > + (vcpu == &hyp_vcpu->vcpu || vcpu == hyp_vcpu->host_vcpu)) > + return pkvm_hyp_vcpu_to_hyp_vm(hyp_vcpu); > + > + return NULL; > +} > + > +/* An unloaded host vCPU's VM is mapped at EL2 only while pinned. */ Could we get the last paragraph of the commit here? As this describes quite well what this is doing. > +struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu) > +{ > + struct pkvm_hyp_vm *hyp_vm; > + struct kvm *kvm; > + > + if (!is_protected_kvm_enabled()) > + return kern_hyp_va(vcpu->kvm); > + > + hyp_vm = loaded_hyp_vm_of(vcpu); > + if (hyp_vm) > + return &hyp_vm->kvm; > + > + kvm = kern_hyp_va(READ_ONCE(vcpu->kvm)); > + if (hyp_pin_shared_mem(kvm, kvm + 1)) > + return NULL; > + > + return kvm; > +} > + > +void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm) > +{ > + if (kvm && is_protected_kvm_enabled() && !loaded_hyp_vm_of(vcpu)) > + hyp_unpin_shared_mem(kvm, kvm + 1); > +} > + It seems strange for pkvm.c to provides function that aren't prefixed with pkvm_ and declared into adjust_pc.h and not pkvm.h. I wonder if adjust_pc.h should't just struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu) { if (is_protected_kvm_enabled()) return pkvm_vcpu_get_kvm() else kern_hyp_va(vcpu->kvm); } > struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle) > { > struct pkvm_hyp_vm *hyp_vm; > -- > 2.39.5 > Beside those nits: Reviewed-by: Vincent Donnefort -- Vincent