Patch "arm: KVM: Fix SMCCC handling of unimplemented SMC/HVC calls" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm-kvm-fix-smccc-handling-of-unimplemented-smc-hvc-calls.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Marc Zyngier <[email protected]>
Date: Tue, 6 Feb 2018 17:56:06 +0000
Subject: arm: KVM: Fix SMCCC handling of unimplemented SMC/HVC calls

From: Marc Zyngier <[email protected]>

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.

---
 arch/arm/kvm/handle_exit.c |   13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

@@ -45,7 +45,7 @@ static int handle_hvc(struct kvm_vcpu *v
 
 	ret = kvm_psci_call(vcpu);
 	if (ret < 0) {
-		kvm_inject_undefined(vcpu);
+		vcpu_set_reg(vcpu, 0, ~0UL);
 		return 1;
 	}
 

@@ -54,7 +54,16 @@ static int handle_hvc(struct kvm_vcpu *v
 
 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;
 }
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/arm-kvm-fix-smccc-handling-of-unimplemented-smc-hvc-calls.patch