supporting sError injection step 2 on Arm64

I disabled DAIF(DEBUG, sError, IRQ, FIQ) in guest kernel mode,
and enabled them in guest user mode.
So, I can make sure all DAIF-s come from guest user mode,
and then the case 'TestBounceStress' can passed on Arm64.

Test steps:
 1, cd pkg/sentry/platform/kvm
 2, bazel test kvm_test --strip=never --test_output=streamed

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

pkg/sentry/platform/kvm/bluepill_arm64.go

@@ -49,7 +49,7 @@ func bluepillArchEnter(context *arch.SignalContext64) (c *vCPU) {
 	regs.Sp = context.Sp
 	regs.Pc = context.Pc
 	regs.Pstate = context.Pstate
-	regs.Pstate &^= uint64(ring0.KernelFlagsClear)
+	regs.Pstate &^= uint64(ring0.PsrFlagsClear)
 	regs.Pstate |= ring0.KernelFlagsSet
 	return
 }
@@ -63,7 +63,7 @@ func bluepillArchExit(c *vCPU, context *arch.SignalContext64) {
 	context.Sp = regs.Sp
 	context.Pc = regs.Pc
 	context.Pstate = regs.Pstate
-	context.Pstate &^= uint64(ring0.UserFlagsClear)
+	context.Pstate &^= uint64(ring0.PsrFlagsClear)
 	context.Pstate |= ring0.UserFlagsSet
 
 	lazyVfp := c.GetLazyVFP()

pkg/sentry/platform/kvm/bluepill_arm64_unsafe.go

@@ -41,7 +41,7 @@ func fpsimdPtr(addr *byte) *arch.FpsimdContext {
 func dieArchSetup(c *vCPU, context *arch.SignalContext64, guestRegs *userRegs) {
 	// If the vCPU is in user mode, we set the stack to the stored stack
 	// value in the vCPU itself. We don't want to unwind the user stack.
-	if guestRegs.Regs.Pstate&ring0.PSR_MODE_MASK == ring0.PSR_MODE_EL0t {
+	if guestRegs.Regs.Pstate&ring0.PsrModeMask == ring0.UserFlagsSet {
 		regs := c.CPU.Registers()
 		context.Regs[0] = regs.Regs[0]
 		context.Sp = regs.Sp

pkg/sentry/platform/kvm/machine_arm64_unsafe.go

@@ -151,12 +151,6 @@ func (c *vCPU) initArchState() error {
 	// the MMIO address base.
 	arm64HypercallMMIOBase = toLocation
 
-	data = ring0.PsrDefaultSet | ring0.KernelFlagsSet
-	reg.id = _KVM_ARM64_REGS_PSTATE
-	if err := c.setOneRegister(&reg); err != nil {
-		return err
-	}
-
 	// Initialize the PCID database.
 	if hasGuestPCID {
 		// Note that NewPCIDs may return a nil table here, in which

pkg/sentry/platform/ring0/aarch64.go

@@ -26,30 +26,31 @@ const (
 	_PMD_PGT_SIZE = 0x4000
 	_PTE_PGT_BASE = 0x7000
 	_PTE_PGT_SIZE = 0x1000
-
-	_PSR_D_BIT = 0x00000200
-	_PSR_A_BIT = 0x00000100
-	_PSR_I_BIT = 0x00000080
-	_PSR_F_BIT = 0x00000040
 )
 
 const (
-	// PSR bits
-	PSR_MODE_EL0t = 0x00000000
-	PSR_MODE_EL1t = 0x00000004
-	PSR_MODE_EL1h = 0x00000005
-	PSR_MODE_MASK = 0x0000000f
+	// DAIF bits:debug, sError, IRQ, FIQ.
+	_PSR_D_BIT      = 0x00000200
+	_PSR_A_BIT      = 0x00000100
+	_PSR_I_BIT      = 0x00000080
+	_PSR_F_BIT      = 0x00000040
+	_PSR_DAIF_SHIFT = 6
+	_PSR_DAIF_MASK  = 0xf << _PSR_DAIF_SHIFT
+
+	// PSR bits.
+	_PSR_MODE_EL0t = 0x00000000
+	_PSR_MODE_EL1t = 0x00000004
+	_PSR_MODE_EL1h = 0x00000005
+	_PSR_MODE_MASK = 0x0000000f
+
+	PsrFlagsClear = _PSR_MODE_MASK | _PSR_DAIF_MASK
+	PsrModeMask   = _PSR_MODE_MASK
 
 	// KernelFlagsSet should always be set in the kernel.
-	KernelFlagsSet = PSR_MODE_EL1h
+	KernelFlagsSet = _PSR_MODE_EL1h | _PSR_D_BIT | _PSR_A_BIT | _PSR_I_BIT | _PSR_F_BIT
 
 	// UserFlagsSet are always set in userspace.
-	UserFlagsSet = PSR_MODE_EL0t
-
-	KernelFlagsClear = PSR_MODE_MASK
-	UserFlagsClear   = PSR_MODE_MASK
-
-	PsrDefaultSet = _PSR_D_BIT | _PSR_A_BIT | _PSR_I_BIT | _PSR_F_BIT
+	UserFlagsSet = _PSR_MODE_EL0t
 )
 
 // Vector is an exception vector.

pkg/sentry/platform/ring0/entry_arm64.s

@@ -312,12 +312,6 @@
 	ISB $15; \
 	DSB $15;
 
-#define IRQ_ENABLE \
-	MSR $2, DAIFSet;
-
-#define IRQ_DISABLE \
-	MSR $2, DAIFClr;
-
 #define VFP_ENABLE \
 	MOVD $FPEN_ENABLE, R0; \
 	WORD $0xd5181040; \ //MSR R0, CPACR_EL1
@@ -509,8 +503,6 @@ 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

pkg/sentry/platform/ring0/kernel_arm64.go

@@ -56,7 +56,7 @@ func (c *CPU) SwitchToUser(switchOpts SwitchOpts) (vector Vector) {
 	// Sanitize registers.
 	regs := switchOpts.Registers
 
-	regs.Pstate &= ^uint64(UserFlagsClear)
+	regs.Pstate &= ^uint64(PsrFlagsClear)
 	regs.Pstate |= UserFlagsSet
 
 	SetTLS(regs.TPIDR_EL0)