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Subject[PATCH] arm64: KVM: Reject non-compliant HVC calls from guest kernel
Date
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@codeaurora.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)
--
Qualcomm Datacenter Technologies, Inc. on behalf of the Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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