Move `safecopy.ReplaceSignalHandler` into `sighandling` package.

PiperOrigin-RevId: 399560357

7 files changed, 43 insertions, 45 deletions

diff --git a/pkg/safecopy/BUILD b/pkg/safecopy/BUILD
index 0a045fc8e..2a1602e2b 100644
--- a/pkg/safecopy/BUILD
+++ b/pkg/safecopy/BUILD
@@ -18,9 +18,9 @@ go_library(
     ],
     visibility = ["//:sandbox"],
     deps = [
-        "//pkg/abi/linux",
         "//pkg/errors",
         "//pkg/errors/linuxerr",
+        "//pkg/sighandling",
         "@org_golang_x_sys//unix:go_default_library",
     ],
 )
diff --git a/pkg/safecopy/safecopy.go b/pkg/safecopy/safecopy.go
index a9711e63d..0dd0aea83 100644
--- a/pkg/safecopy/safecopy.go
+++ b/pkg/safecopy/safecopy.go
@@ -23,6 +23,7 @@ import (
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/errors"
 	"gvisor.dev/gvisor/pkg/errors/linuxerr"
+	"gvisor.dev/gvisor/pkg/sighandling"
 )
 
 // SegvError is returned when a safecopy function receives SIGSEGV.
@@ -132,10 +133,10 @@ func initializeAddresses() {
 
 func init() {
 	initializeAddresses()
-	if err := ReplaceSignalHandler(unix.SIGSEGV, addrOfSignalHandler(), &savedSigSegVHandler); err != nil {
+	if err := sighandling.ReplaceSignalHandler(unix.SIGSEGV, addrOfSignalHandler(), &savedSigSegVHandler); err != nil {
 		panic(fmt.Sprintf("Unable to set handler for SIGSEGV: %v", err))
 	}
-	if err := ReplaceSignalHandler(unix.SIGBUS, addrOfSignalHandler(), &savedSigBusHandler); err != nil {
+	if err := sighandling.ReplaceSignalHandler(unix.SIGBUS, addrOfSignalHandler(), &savedSigBusHandler); err != nil {
 		panic(fmt.Sprintf("Unable to set handler for SIGBUS: %v", err))
 	}
 	linuxerr.AddErrorUnwrapper(func(e error) (*errors.Error, bool) {
diff --git a/pkg/safecopy/safecopy_unsafe.go b/pkg/safecopy/safecopy_unsafe.go
index 2365b2c0d..15f84abea 100644
--- a/pkg/safecopy/safecopy_unsafe.go
+++ b/pkg/safecopy/safecopy_unsafe.go
@@ -20,7 +20,6 @@ import (
 	"unsafe"
 
 	"golang.org/x/sys/unix"
-	"gvisor.dev/gvisor/pkg/abi/linux"
 )
 
 // maxRegisterSize is the maximum register size used in memcpy and memclr. It
@@ -332,39 +331,3 @@ func errorFromFaultSignal(addr uintptr, sig int32) error {
 		panic(fmt.Sprintf("safecopy got unexpected signal %d at address %#x", sig, addr))
 	}
 }
-
-// ReplaceSignalHandler replaces the existing signal handler for the provided
-// signal with the one that handles faults in safecopy-protected functions.
-//
-// It stores the value of the previously set handler in previous.
-//
-// This function will be called on initialization in order to install safecopy
-// handlers for appropriate signals. These handlers will call the previous
-// handler however, and if this is function is being used externally then the
-// same courtesy is expected.
-func ReplaceSignalHandler(sig unix.Signal, handler uintptr, previous *uintptr) error {
-	var sa linux.SigAction
-	const maskLen = 8
-
-	// Get the existing signal handler information, and save the current
-	// handler. Once we replace it, we will use this pointer to fall back to
-	// it when we receive other signals.
-	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(sig), 0, uintptr(unsafe.Pointer(&sa)), maskLen, 0, 0); e != 0 {
-		return e
-	}
-
-	// Fail if there isn't a previous handler.
-	if sa.Handler == 0 {
-		return fmt.Errorf("previous handler for signal %x isn't set", sig)
-	}
-
-	*previous = uintptr(sa.Handler)
-
-	// Install our own handler.
-	sa.Handler = uint64(handler)
-	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(sig), uintptr(unsafe.Pointer(&sa)), 0, maskLen, 0, 0); e != 0 {
-		return e
-	}
-
-	return nil
-}
diff --git a/pkg/sentry/platform/kvm/BUILD b/pkg/sentry/platform/kvm/BUILD
index a26f54269..834d72408 100644
--- a/pkg/sentry/platform/kvm/BUILD
+++ b/pkg/sentry/platform/kvm/BUILD
@@ -63,7 +63,6 @@ go_library(
         "//pkg/procid",
         "//pkg/ring0",
         "//pkg/ring0/pagetables",
-        "//pkg/safecopy",
         "//pkg/seccomp",
         "//pkg/sentry/arch",
         "//pkg/sentry/arch/fpu",
@@ -71,6 +70,7 @@ go_library(
         "//pkg/sentry/platform",
         "//pkg/sentry/platform/interrupt",
         "//pkg/sentry/time",
+        "//pkg/sighandling",
         "//pkg/sync",
         "@org_golang_x_sys//unix:go_default_library",
     ],
diff --git a/pkg/sentry/platform/kvm/bluepill.go b/pkg/sentry/platform/kvm/bluepill.go
index 826997e77..5be2215ed 100644
--- a/pkg/sentry/platform/kvm/bluepill.go
+++ b/pkg/sentry/platform/kvm/bluepill.go
@@ -19,8 +19,8 @@ import (
 
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/ring0"
-	"gvisor.dev/gvisor/pkg/safecopy"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sighandling"
 )
 
 // bluepill enters guest mode.
@@ -97,7 +97,7 @@ func (c *vCPU) die(context *arch.SignalContext64, msg string) {
 
 func init() {
 	// Install the handler.
-	if err := safecopy.ReplaceSignalHandler(bluepillSignal, addrOfSighandler(), &savedHandler); err != nil {
+	if err := sighandling.ReplaceSignalHandler(bluepillSignal, addrOfSighandler(), &savedHandler); err != nil {
 		panic(fmt.Sprintf("Unable to set handler for signal %d: %v", bluepillSignal, err))
 	}
 
diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go
index dcf34015d..f1f7e4ea4 100644
--- a/pkg/sentry/platform/kvm/machine.go
+++ b/pkg/sentry/platform/kvm/machine.go
@@ -28,9 +28,9 @@ import (
 	"gvisor.dev/gvisor/pkg/procid"
 	"gvisor.dev/gvisor/pkg/ring0"
 	"gvisor.dev/gvisor/pkg/ring0/pagetables"
-	"gvisor.dev/gvisor/pkg/safecopy"
 	"gvisor.dev/gvisor/pkg/seccomp"
 	ktime "gvisor.dev/gvisor/pkg/sentry/time"
+	"gvisor.dev/gvisor/pkg/sighandling"
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
@@ -723,7 +723,7 @@ func addrOfSigsysHandler() uintptr
 func seccompMmapRules(m *machine) {
 	seccompMmapRulesOnce.Do(func() {
 		// Install the handler.
-		if err := safecopy.ReplaceSignalHandler(unix.SIGSYS, addrOfSigsysHandler(), &savedSigsysHandler); err != nil {
+		if err := sighandling.ReplaceSignalHandler(unix.SIGSYS, addrOfSigsysHandler(), &savedSigsysHandler); err != nil {
 			panic(fmt.Sprintf("Unable to set handler for signal %d: %v", bluepillSignal, err))
 		}
 		rules := []seccomp.RuleSet{}
diff --git a/pkg/sighandling/sighandling_unsafe.go b/pkg/sighandling/sighandling_unsafe.go
index 3fe5c6770..7deeda042 100644
--- a/pkg/sighandling/sighandling_unsafe.go
+++ b/pkg/sighandling/sighandling_unsafe.go
@@ -15,6 +15,7 @@
 package sighandling
 
 import (
+	"fmt"
 	"unsafe"
 
 	"golang.org/x/sys/unix"
@@ -37,3 +38,36 @@ func IgnoreChildStop() error {
 
 	return nil
 }
+
+// ReplaceSignalHandler replaces the existing signal handler for the provided
+// signal with the function pointer at `handler`. This bypasses the Go runtime
+// signal handlers, and should only be used for low-level signal handlers where
+// use of signal.Notify is not appropriate.
+//
+// It stores the value of the previously set handler in previous.
+func ReplaceSignalHandler(sig unix.Signal, handler uintptr, previous *uintptr) error {
+	var sa linux.SigAction
+	const maskLen = 8
+
+	// Get the existing signal handler information, and save the current
+	// handler. Once we replace it, we will use this pointer to fall back to
+	// it when we receive other signals.
+	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(sig), 0, uintptr(unsafe.Pointer(&sa)), maskLen, 0, 0); e != 0 {
+		return e
+	}
+
+	// Fail if there isn't a previous handler.
+	if sa.Handler == 0 {
+		return fmt.Errorf("previous handler for signal %x isn't set", sig)
+	}
+
+	*previous = uintptr(sa.Handler)
+
+	// Install our own handler.
+	sa.Handler = uint64(handler)
+	if _, _, e := unix.RawSyscall6(unix.SYS_RT_SIGACTION, uintptr(sig), uintptr(unsafe.Pointer(&sa)), 0, maskLen, 0, 0); e != 0 {
+		return e
+	}
+
+	return nil
+}