arm: KVM: Fix SMCCC handling of unimplemented SMC/HVC calls

commit 20e8175d246e9f9deb377f2784b3e7dfb2ad3e86 upstream.

KVM doesn't follow the SMCCC when it comes to unimplemented calls,
and inject an UNDEF instead of returning an error. Since firmware
calls are now used for security mitigation, they are becoming more
common, and the undef is counter productive.

Instead, let's follow the SMCCC which states that -1 must be returned
to the caller when getting an unknown function number.

Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm/kvm/handle_exit.c b/arch/arm/kvm/handle_exit.c
index 76be5701f9d6ab8d1619e6cf2e94e880e9a58c9f..910bd8dabb3c038932abec060bc66da8834aeb68 100644 (file)
--- a/arch/arm/kvm/handle_exit.c
+++ b/arch/arm/kvm/handle_exit.c
@@ -38,7 +38,7 @@ static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
 
        ret = kvm_hvc_call_handler(vcpu);
        if (ret < 0) {
-               kvm_inject_undefined(vcpu);
+               vcpu_set_reg(vcpu, 0, ~0UL);
                return 1;
        }
 
@@ -47,7 +47,16 @@ static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
 
 static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
-       kvm_inject_undefined(vcpu);
+       /*
+        * "If an SMC instruction executed at Non-secure EL1 is
+        * trapped to EL2 because HCR_EL2.TSC is 1, the exception is a
+        * Trap exception, not a Secure Monitor Call exception [...]"
+        *
+        * We need to advance the PC after the trap, as it would
+        * otherwise return to the same address...
+        */
+       vcpu_set_reg(vcpu, 0, ~0UL);
+       kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
        return 1;
 }