linux-kernel - [PATCH 3.16 208/254] arm64: KVM: Fix SMCCC handling of unimplemented SMC/HVC calls

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Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Christoffer Dall" <christoffer.dall@...aro.org>,
        "Marc Zyngier" <marc.zyngier@....com>
Subject: [PATCH 3.16 208/254] arm64: KVM: Fix SMCCC handling of
 unimplemented SMC/HVC calls

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Marc Zyngier <marc.zyngier@....com>

commit acfb3b883f6d6a4b5d27ad7fdded11f6a09ae6dd 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.

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Christoffer Dall <christoffer.dall@...aro.org>
[bwh: Backported to 3.16: use vcpu_reg()]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm64/kvm/handle_exit.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -34,7 +34,7 @@ static int handle_hvc(struct kvm_vcpu *v
 
 	ret = kvm_psci_call(vcpu);
 	if (ret < 0) {
-		kvm_inject_undefined(vcpu);
+		*vcpu_reg(vcpu, 0) = ~0UL;
 		return 1;
 	}
 
@@ -43,7 +43,7 @@ static int handle_hvc(struct kvm_vcpu *v
 
 static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
-	kvm_inject_undefined(vcpu);
+	*vcpu_reg(vcpu, 0) = ~0UL;
 	return 1;
 }