allow guest user applications read ctr_el0 on Arm64

At present, when doing syscall_kvm test, we need to
enable the function of ESR_ELx_SYS64_ISS_SYS_CTR_READ to
successfully pass the test.

I set SCTLR_EL1.UCT==1, so that the related cases can passed.

Signed-off-by: Bin Lu <bin.lu@arm.com>

pkg/sentry/platform/kvm/machine_arm64_unsafe.go

@@ -78,19 +78,6 @@ func (c *vCPU) initArchState() error {
 		return err
 	}
 
-	// sctlr_el1
-	regGet.id = _KVM_ARM64_REGS_SCTLR_EL1
-	if err := c.getOneRegister(&regGet); err != nil {
-		return err
-	}
-
-	dataGet |= (_SCTLR_M | _SCTLR_C | _SCTLR_I)
-	data = dataGet
-	reg.id = _KVM_ARM64_REGS_SCTLR_EL1
-	if err := c.setOneRegister(&reg); err != nil {
-		return err
-	}
-
 	// tcr_el1
 	data = _TCR_TXSZ_VA48 | _TCR_CACHE_FLAGS | _TCR_SHARED | _TCR_TG_FLAGS | _TCR_ASID16 | _TCR_IPS_40BITS
 	reg.id = _KVM_ARM64_REGS_TCR_EL1

pkg/sentry/platform/ring0/entry_arm64.s

@@ -40,6 +40,14 @@
 
 #define FPEN_ENABLE (FPEN_NOTRAP << FPEN_SHIFT)
 
+// sctlr_el1: system control register el1.
+#define SCTLR_M         1 << 0
+#define SCTLR_C         1 << 2
+#define SCTLR_I         1 << 12
+#define SCTLR_UCT       1 << 15
+
+#define SCTLR_EL1_DEFAULT       (SCTLR_M | SCTLR_C | SCTLR_I | SCTLR_UCT)
+
 // Saves a register set.
 //
 // This is a macro because it may need to executed in contents where a stack is
@@ -496,6 +504,11 @@ TEXT ·kernelExitToEl1(SB),NOSPLIT,$0
 // Start is the CPU entrypoint.
 TEXT ·Start(SB),NOSPLIT,$0
 	IRQ_DISABLE
+
+	// Init.
+	MOVD $SCTLR_EL1_DEFAULT, R1
+	MSR R1, SCTLR_EL1
+
 	MOVD R8, RSV_REG
 	ORR $0xffff000000000000, RSV_REG, RSV_REG
 	WORD $0xd518d092        //MSR R18, TPIDR_EL1