6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Fuad Tabba [ Upstream commit cf533b4d3630b229d78ad55567c5db2f365052a2 ] 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/ Reviewed-by: Vincent Donnefort Reviewed-by: Joey Gouly Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba Link: https://patch.msgid.link/20261001135711.1640520-3-fuad.tabba@linux.dev Signed-off-by: Marc Zyngier Signed-off-by: Sasha Levin --- arch/arm64/kvm/hyp/exception.c | 5 ++- arch/arm64/kvm/hyp/include/hyp/adjust_pc.h | 28 ++++++++++++++++ arch/arm64/kvm/hyp/include/nvhe/pkvm.h | 2 ++ arch/arm64/kvm/hyp/nvhe/pkvm.c | 37 ++++++++++++++++++++++ 4 files changed, 71 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c index bef40ddb16dbc..c041142896e35 100644 --- a/arch/arm64/kvm/hyp/exception.c +++ b/arch/arm64/kvm/hyp/exception.c @@ -86,6 +86,7 @@ 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); @@ -125,8 +126,10 @@ 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..f55950ee2a7e4 100644 --- a/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h +++ b/arch/arm64/kvm/hyp/include/hyp/adjust_pc.h @@ -13,6 +13,34 @@ #include #include +#ifdef __KVM_NVHE_HYPERVISOR__ +#include + +/* Under pKVM a host vCPU's ->kvm is host-writable. */ +static inline struct kvm *vcpu_get_kvm(struct kvm_vcpu *vcpu) +{ + if (is_protected_kvm_enabled()) + return pkvm_vcpu_get_kvm(vcpu); + + return kern_hyp_va(vcpu->kvm); +} + +static inline void vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm) +{ + if (is_protected_kvm_enabled()) + pkvm_vcpu_put_kvm(vcpu, 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/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h index 184ad7a399507..25b2f477bb5b2 100644 --- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h +++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h @@ -79,6 +79,8 @@ struct pkvm_hyp_vcpu *pkvm_load_hyp_vcpu(pkvm_handle_t handle, unsigned int vcpu_idx); void pkvm_put_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu); struct pkvm_hyp_vcpu *pkvm_get_loaded_hyp_vcpu(void); +struct kvm *pkvm_vcpu_get_kvm(struct kvm_vcpu *vcpu); +void pkvm_vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm); struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle); struct pkvm_hyp_vm *get_np_pkvm_hyp_vm(pkvm_handle_t handle); diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c index bf0250806a781..136c4008b9363 100644 --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c @@ -306,6 +306,43 @@ struct pkvm_hyp_vcpu *pkvm_get_loaded_hyp_vcpu(void) } +static struct pkvm_hyp_vm *pkvm_get_loaded_hyp_vm(struct kvm_vcpu *vcpu) +{ + 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; +} + +/* + * A loaded vCPU's VM is the hyp VM. An unloaded host vCPU's is mapped at + * EL2 only while pinned, so it's read once and pinned; the pin fails for + * memory the host isn't sharing. + */ +struct kvm *pkvm_vcpu_get_kvm(struct kvm_vcpu *vcpu) +{ + struct pkvm_hyp_vm *hyp_vm = pkvm_get_loaded_hyp_vm(vcpu); + struct kvm *kvm; + + 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 pkvm_vcpu_put_kvm(struct kvm_vcpu *vcpu, struct kvm *kvm) +{ + if (kvm && !pkvm_get_loaded_hyp_vm(vcpu)) + hyp_unpin_shared_mem(kvm, kvm + 1); +} + struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle) { struct pkvm_hyp_vm *hyp_vm; -- 2.53.0