KVM: arm64: Save the host's PtrAuth keys in non-preemptible context

When using the PtrAuth feature in a guest, we need to save the host's
keys before allowing the guest to program them. For that, we dump
them in a per-CPU data structure (the so called host context).

But both call sites that do this are in preemptible context,
which may end up in disaster should the vcpu thread get preempted
before reentering the guest.

Instead, save the keys eagerly on each vcpu_load(). This has an
increased overhead, but is at least safe.

Cc: stable@vger.kernel.org
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index a30b4eec7cb40048c92d9d4261765446c2365af8..977843e4d5fb79f3c9b31fff3d403f10039e507a 100644 (file)
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -112,12 +112,6 @@ static inline void vcpu_ptrauth_disable(struct kvm_vcpu *vcpu)
        vcpu->arch.hcr_el2 &= ~(HCR_API | HCR_APK);
 }
 
-static inline void vcpu_ptrauth_setup_lazy(struct kvm_vcpu *vcpu)
-{
-       if (vcpu_has_ptrauth(vcpu))
-               vcpu_ptrauth_disable(vcpu);
-}
-
 static inline unsigned long vcpu_get_vsesr(struct kvm_vcpu *vcpu)
 {
        return vcpu->arch.vsesr_el2;

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index d6988401c22a56171361e12033e8c6efe0f47fa2..152049c5055dcdeb6fda9254b5d340f4cf854b06 100644 (file)
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -337,6 +337,12 @@ void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
        preempt_enable();
 }
 
+#define __ptrauth_save_key(regs, key)                                          \
+({                                                                             \
+       regs[key ## KEYLO_EL1] = read_sysreg_s(SYS_ ## key ## KEYLO_EL1);       \
+       regs[key ## KEYHI_EL1] = read_sysreg_s(SYS_ ## key ## KEYHI_EL1);       \
+})
+
 void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
        int *last_ran;
@@ -370,7 +376,17 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
        else
                vcpu_set_wfx_traps(vcpu);
 
-       vcpu_ptrauth_setup_lazy(vcpu);
+       if (vcpu_has_ptrauth(vcpu)) {
+               struct kvm_cpu_context *ctxt = vcpu->arch.host_cpu_context;
+
+               __ptrauth_save_key(ctxt->sys_regs, APIA);
+               __ptrauth_save_key(ctxt->sys_regs, APIB);
+               __ptrauth_save_key(ctxt->sys_regs, APDA);
+               __ptrauth_save_key(ctxt->sys_regs, APDB);
+               __ptrauth_save_key(ctxt->sys_regs, APGA);
+
+               vcpu_ptrauth_disable(vcpu);
+       }
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index eb194696ef62250535648be848e9b725105802d1..065251efa2e6a2d57ec7c98b079617402ab57045 100644 (file)
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -162,31 +162,16 @@ static int handle_sve(struct kvm_vcpu *vcpu, struct kvm_run *run)
        return 1;
 }
 
-#define __ptrauth_save_key(regs, key)                                          \
-({                                                                             \
-       regs[key ## KEYLO_EL1] = read_sysreg_s(SYS_ ## key ## KEYLO_EL1);       \
-       regs[key ## KEYHI_EL1] = read_sysreg_s(SYS_ ## key ## KEYHI_EL1);       \
-})
-
 /*
  * Handle the guest trying to use a ptrauth instruction, or trying to access a
  * ptrauth register.
  */
 void kvm_arm_vcpu_ptrauth_trap(struct kvm_vcpu *vcpu)
 {
-       struct kvm_cpu_context *ctxt;
-
-       if (vcpu_has_ptrauth(vcpu)) {
+       if (vcpu_has_ptrauth(vcpu))
                vcpu_ptrauth_enable(vcpu);
-               ctxt = vcpu->arch.host_cpu_context;
-               __ptrauth_save_key(ctxt->sys_regs, APIA);
-               __ptrauth_save_key(ctxt->sys_regs, APIB);
-               __ptrauth_save_key(ctxt->sys_regs, APDA);
-               __ptrauth_save_key(ctxt->sys_regs, APDB);
-               __ptrauth_save_key(ctxt->sys_regs, APGA);
-       } else {
+       else
                kvm_inject_undefined(vcpu);
-       }
 }
 
 /*