Merge pull request #4377 from avagin:kvm-if-flag

PiperOrigin-RevId: 335122704

4 files changed, 52 insertions, 6 deletions

diff --git a/pkg/sentry/platform/kvm/bluepill_amd64_unsafe.go b/pkg/sentry/platform/kvm/bluepill_amd64_unsafe.go
index 03a98512e..0a54dd30d 100644
--- a/pkg/sentry/platform/kvm/bluepill_amd64_unsafe.go
+++ b/pkg/sentry/platform/kvm/bluepill_amd64_unsafe.go
@@ -83,5 +83,34 @@ func bluepillStopGuest(c *vCPU) {
 //
 //go:nosplit
 func bluepillReadyStopGuest(c *vCPU) bool {
-	return c.runData.readyForInterruptInjection != 0
+	if c.runData.readyForInterruptInjection == 0 {
+		return false
+	}
+
+	if c.runData.ifFlag == 0 {
+		// This is impossible if readyForInterruptInjection is 1.
+		throw("interrupts are disabled")
+	}
+
+	// Disable interrupts if we are in the kernel space.
+	//
+	// When the Sentry switches into the kernel mode, it disables
+	// interrupts. But when goruntime switches on a goroutine which has
+	// been saved in the host mode, it restores flags and this enables
+	// interrupts.  See the comment of UserFlagsSet for more details.
+	uregs := userRegs{}
+	err := c.getUserRegisters(&uregs)
+	if err != 0 {
+		throw("failed to get user registers")
+	}
+
+	if ring0.IsKernelFlags(uregs.RFLAGS) {
+		uregs.RFLAGS &^= ring0.KernelFlagsClear
+		err = c.setUserRegisters(&uregs)
+		if err != 0 {
+			throw("failed to set user registers")
+		}
+		return false
+	}
+	return true
 }
diff --git a/pkg/sentry/platform/kvm/kvm_const.go b/pkg/sentry/platform/kvm/kvm_const.go
index 5c4b18899..5f627a016 100644
--- a/pkg/sentry/platform/kvm/kvm_const.go
+++ b/pkg/sentry/platform/kvm/kvm_const.go
@@ -32,6 +32,7 @@ const (
 	_KVM_SET_REGS               = 0x4090ae82
 	_KVM_SET_SREGS              = 0x4138ae84
 	_KVM_GET_REGS               = 0x8090ae81
+	_KVM_GET_SREGS              = 0x8138ae83
 	_KVM_GET_SUPPORTED_CPUID    = 0xc008ae05
 	_KVM_SET_CPUID2             = 0x4008ae90
 	_KVM_SET_SIGNAL_MASK        = 0x4004ae8b
diff --git a/pkg/sentry/platform/kvm/machine_amd64.go b/pkg/sentry/platform/kvm/machine_amd64.go
index 6849ab113..54e721bb1 100644
--- a/pkg/sentry/platform/kvm/machine_amd64.go
+++ b/pkg/sentry/platform/kvm/machine_amd64.go
@@ -153,8 +153,8 @@ func (c *vCPU) initArchState() error {
 	}
 
 	// Set the user registers.
-	if err := c.setUserRegisters(&kernelUserRegs); err != nil {
-		return err
+	if errno := c.setUserRegisters(&kernelUserRegs); errno != 0 {
+		return fmt.Errorf("error setting user registers: %v", errno)
 	}
 
 	// Allocate some floating point state save area for the local vCPU.
diff --git a/pkg/sentry/platform/kvm/machine_amd64_unsafe.go b/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
index 290f035dd..330f29065 100644
--- a/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
@@ -137,15 +137,17 @@ func (c *vCPU) setSignalMask() error {
 }
 
 // setUserRegisters sets user registers in the vCPU.
-func (c *vCPU) setUserRegisters(uregs *userRegs) error {
+//
+//go:nosplit
+func (c *vCPU) setUserRegisters(uregs *userRegs) syscall.Errno {
 	if _, _, errno := syscall.RawSyscall(
 		syscall.SYS_IOCTL,
 		uintptr(c.fd),
 		_KVM_SET_REGS,
 		uintptr(unsafe.Pointer(uregs))); errno != 0 {
-		return fmt.Errorf("error setting user registers: %v", errno)
+		return errno
 	}
-	return nil
+	return 0
 }
 
 // getUserRegisters reloads user registers in the vCPU.
@@ -175,3 +177,17 @@ func (c *vCPU) setSystemRegisters(sregs *systemRegs) error {
 	}
 	return nil
 }
+
+// getSystemRegisters sets system registers.
+//
+//go:nosplit
+func (c *vCPU) getSystemRegisters(sregs *systemRegs) syscall.Errno {
+	if _, _, errno := syscall.RawSyscall(
+		syscall.SYS_IOCTL,
+		uintptr(c.fd),
+		_KVM_GET_SREGS,
+		uintptr(unsafe.Pointer(sregs))); errno != 0 {
+		return errno
+	}
+	return 0
+}