From 2955bcc8c309bb8f2c773db4798649aa802a491f Mon Sep 17 00:00:00 2001 From: Dave Martin Date: Fri, 15 Jun 2018 16:47:26 +0100 Subject: [PATCH] KVM: arm64: Avoid mistaken attempts to save SVE state for vcpus Commit e6b673b ("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") uses fpsimd_save() to save the FPSIMD state for a vcpu when scheduling the vcpu out. However, currently current's value of TIF_SVE is restored before calling fpsimd_save() which means that fpsimd_save() may erroneously attempt to save SVE state from the vcpu. This enables current's vector state to be polluted with guest data. current->thread.sve_state may be unallocated or not large enough, so this can also trigger a NULL dereference or buffer overrun. Instead of this, TIF_SVE should be configured properly for the guest when calling fpsimd_save() with the vcpu context loaded. This patch ensures this by delaying restoration of current's TIF_SVE until after the call to fpsimd_save(). Fixes: e6b673b741ea ("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") Signed-off-by: Dave Martin Signed-off-by: Marc Zyngier --- arch/arm64/kvm/fpsimd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 98d19d1afa50..aac7808ce216 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -103,9 +103,6 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) local_irq_save(flags); - update_thread_flag(TIF_SVE, - vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE); - if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) { /* Clean guest FP state to memory and invalidate cpu view */ fpsimd_save(); @@ -124,5 +121,8 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0); } + update_thread_flag(TIF_SVE, + vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE); + local_irq_restore(flags); }