5 files changed, 44 insertions, 2 deletions
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 0b53c72e7591..aea01a09eb94 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -30,6 +30,7 @@
 #define ARM_EXCEPTION_IRQ	  0
 #define ARM_EXCEPTION_EL1_SERROR  1
 #define ARM_EXCEPTION_TRAP	  2
+#define ARM_EXCEPTION_IL	  3
 /* The hyp-stub will return this for any kvm_call_hyp() call */
 #define ARM_EXCEPTION_HYP_GONE	  HVC_STUB_ERR
 
diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 177b851ca6d9..ff35ac1258eb 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -25,6 +25,9 @@
 #define CurrentEL_EL1		(1 << 2)
 #define CurrentEL_EL2		(2 << 2)
 
+/* Additional SPSR bits not exposed in the UABI */
+#define PSR_IL_BIT		(1 << 20)
+
 /* AArch32-specific ptrace requests */
 #define COMPAT_PTRACE_GETREGS		12
 #define COMPAT_PTRACE_SETREGS		13
diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index e5e741bfffe1..35a81bebd02b 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -284,6 +284,13 @@ int handle_exit(struct kvm_vcpu *vcpu, struct kvm_run *run,
 		 */
 		run->exit_reason = KVM_EXIT_FAIL_ENTRY;
 		return 0;
+	case ARM_EXCEPTION_IL:
+		/*
+		 * We attempted an illegal exception return.  Guest state must
+		 * have been corrupted somehow.  Give up.
+		 */
+		run->exit_reason = KVM_EXIT_FAIL_ENTRY;
+		return -EINVAL;
 	default:
 		kvm_pr_unimpl("Unsupported exception type: %d",
 			      exception_index);
diff --git a/arch/arm64/kvm/hyp/hyp-entry.S b/arch/arm64/kvm/hyp/hyp-entry.S
index 24b4fbafe3e4..b1f14f736962 100644
--- a/arch/arm64/kvm/hyp/hyp-entry.S
+++ b/arch/arm64/kvm/hyp/hyp-entry.S
@@ -162,6 +162,20 @@ el1_error:
 	mov	x0, #ARM_EXCEPTION_EL1_SERROR
 	b	__guest_exit
 
+el2_sync:
+	/* Check for illegal exception return, otherwise panic */
+	mrs	x0, spsr_el2
+
+	/* if this was something else, then panic! */
+	tst	x0, #PSR_IL_BIT
+	b.eq	__hyp_panic
+
+	/* Let's attempt a recovery from the illegal exception return */
+	get_vcpu_ptr	x1, x0
+	mov	x0, #ARM_EXCEPTION_IL
+	b	__guest_exit
+
+
 el2_error:
 	ldp	x0, x1, [sp], #16
 
@@ -240,7 +254,7 @@ ENTRY(__kvm_hyp_vector)
 	invalid_vect	el2t_fiq_invalid	// FIQ EL2t
 	invalid_vect	el2t_error_invalid	// Error EL2t
 
-	invalid_vect	el2h_sync_invalid	// Synchronous EL2h
+	valid_vect	el2_sync		// Synchronous EL2h
 	invalid_vect	el2h_irq_invalid	// IRQ EL2h
 	invalid_vect	el2h_fiq_invalid	// FIQ EL2h
 	valid_vect	el2_error		// Error EL2h
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index 9ce223944983..8dc285318204 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -152,8 +152,25 @@ static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
 static void __hyp_text
 __sysreg_restore_el2_return_state(struct kvm_cpu_context *ctxt)
 {
+	u64 pstate = ctxt->gp_regs.regs.pstate;
+	u64 mode = pstate & PSR_AA32_MODE_MASK;
+
+	/*
+	 * Safety check to ensure we're setting the CPU up to enter the guest
+	 * in a less privileged mode.
+	 *
+	 * If we are attempting a return to EL2 or higher in AArch64 state,
+	 * program SPSR_EL2 with M=EL2h and the IL bit set which ensures that
+	 * we'll take an illegal exception state exception immediately after
+	 * the ERET to the guest.  Attempts to return to AArch32 Hyp will
+	 * result in an illegal exception return because EL2's execution state
+	 * is determined by SCR_EL3.RW.
+	 */
+	if (!(mode & PSR_MODE32_BIT) && mode >= PSR_MODE_EL2t)
+		pstate = PSR_MODE_EL2h | PSR_IL_BIT;
+
 	write_sysreg_el2(ctxt->gp_regs.regs.pc,		elr);
-	write_sysreg_el2(ctxt->gp_regs.regs.pstate,	spsr);
+	write_sysreg_el2(pstate,			spsr);
 
 	if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN))
 		write_sysreg_s(ctxt->sys_regs[DISR_EL1], SYS_VDISR_EL2);