linux-kernel - [PATCH] arm64: KVM: Reject non-compliant HVC calls from guest kernel

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Date:   Mon,  7 Aug 2017 14:03:28 -0500
From:   Shanker Donthineni <shankerd@...eaurora.org>
To:     Marc Zyngier <marc.zyngier@....com>,
        Christoffer Dall <christoffer.dall@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        kvmarm <kvmarm@...ts.cs.columbia.edu>, kvm <kvm@...r.kernel.org>,
        Shanker Donthineni <shankerd@...eaurora.org>
Subject: [PATCH] arm64: KVM: Reject non-compliant HVC calls from guest kernel

The SMC/HVC instructions with an immediate value non-zero are not compliant
according to 'SMC calling convention system software document'. Add a
validation check in handle_hvc() to avoid malicious HVC calls from VM, and
inject an undefined instruction for those calls.

http://infocenter.arm.com/help/topic/com.arm.doc.den0028b/ARM_DEN0028B_SMC_Calling_Convention.pdf

Signed-off-by: Shanker Donthineni <shankerd@...eaurora.org>
---
 arch/arm64/include/asm/esr.h |  4 ++++
 arch/arm64/kvm/handle_exit.c | 12 +++++++-----
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
index 8cabd57..fa988e5 100644
--- a/arch/arm64/include/asm/esr.h
+++ b/arch/arm64/include/asm/esr.h
@@ -107,6 +107,9 @@
 #define ESR_ELx_AR 		(UL(1) << 14)
 #define ESR_ELx_CM 		(UL(1) << 8)
 
+/* ISS field definitions for HVC/SVC instruction execution traps */
+#define ESR_HVC_IMMEDIATE(esr)	((esr) & 0xFFFF)
+
 /* ISS field definitions for exceptions taken in to Hyp */
 #define ESR_ELx_CV		(UL(1) << 24)
 #define ESR_ELx_COND_SHIFT	(20)
@@ -114,6 +117,7 @@
 #define ESR_ELx_WFx_ISS_WFE	(UL(1) << 0)
 #define ESR_ELx_xVC_IMM_MASK	((1UL << 16) - 1)
 
+
 /* ESR value templates for specific events */
 
 /* BRK instruction trap from AArch64 state */
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 17d8a16..a900dcd 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -42,13 +42,15 @@ static int handle_hvc(struct kvm_vcpu *vcpu, struct kvm_run *run)
 			    kvm_vcpu_hvc_get_imm(vcpu));
 	vcpu->stat.hvc_exit_stat++;
 
-	ret = kvm_psci_call(vcpu);
-	if (ret < 0) {
-		kvm_inject_undefined(vcpu);
-		return 1;
+	/* HVC immediate value must be zero for all compliant calls */
+	if (!ESR_HVC_IMMEDIATE(kvm_vcpu_get_hsr(vcpu))) {
+		ret = kvm_psci_call(vcpu);
+		if (ret >= 0)
+			return ret;
 	}
 
-	return ret;
+	kvm_inject_undefined(vcpu);
+	return 1;
 }
 
 static int handle_smc(struct kvm_vcpu *vcpu, struct kvm_run *run)
-- 
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