linux-kernel - [PATCH 4.14 079/195] [Variant 2/Spectre-v2] arm64: KVM: Increment PC after handling an SMC trap

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Message-Id: <20180215151709.640731876@linuxfoundation.org>
Date:   Thu, 15 Feb 2018 16:16:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH 4.14 079/195] [Variant 2/Spectre-v2] arm64: KVM: Increment PC after handling an SMC trap

4.14-stable review patch.  If anyone has any objections, please let me know.

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

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


Commit f5115e8869e1 upstream.

When handling an SMC trap, the "preferred return address" is set
to that of the SMC, and not the next PC (which is a departure from
the behaviour of an SMC that isn't trapped).

Increment PC in the handler, as the guest is otherwise forever
stuck...

Cc: stable@...r.kernel.org
Fixes: acfb3b883f6d ("arm64: KVM: Fix SMCCC handling of unimplemented SMC/HVC calls")
Reviewed-by: Christoffer Dall <christoffer.dall@...aro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/kvm/handle_exit.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -53,7 +53,16 @@ static int handle_hvc(struct kvm_vcpu *v
 
 static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
+	/*
+	 * "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;
 }