Implement rseq(2)

PiperOrigin-RevId: 288342928

1 files changed, 334 insertions, 49 deletions

diff --git a/pkg/sentry/kernel/rseq.go b/pkg/sentry/kernel/rseq.go
index 24ea002ba..b14429854 100644
--- a/pkg/sentry/kernel/rseq.go
+++ b/pkg/sentry/kernel/rseq.go
@@ -15,17 +15,29 @@
 package kernel
 
 import (
+	"fmt"
+
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/hostcpu"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
-// Restartable sequences, as described in https://lwn.net/Articles/650333/.
+// Restartable sequences.
+//
+// We support two different APIs for restartable sequences.
+//
+//  1. The upstream interface added in v4.18.
+//  2. The interface described in https://lwn.net/Articles/650333/.
+//
+// Throughout this file and other parts of the kernel, the latter is referred
+// to as "old rseq". This interface was never merged upstream, but is supported
+// for a limited set of applications that use it regardless.
 
-// RSEQCriticalRegion describes a restartable sequence critical region.
+// OldRSeqCriticalRegion describes an old rseq critical region.
 //
 // +stateify savable
-type RSEQCriticalRegion struct {
+type OldRSeqCriticalRegion struct {
 	// When a task in this thread group has its CPU preempted (as defined by
 	// platform.ErrContextCPUPreempted) or has a signal delivered to an
 	// application handler while its instruction pointer is in CriticalSection,
@@ -35,86 +47,359 @@ type RSEQCriticalRegion struct {
 	Restart         usermem.Addr
 }
 
-// RSEQAvailable returns true if t supports restartable sequences.
-func (t *Task) RSEQAvailable() bool {
+// RSeqAvailable returns true if t supports (old and new) restartable sequences.
+func (t *Task) RSeqAvailable() bool {
 	return t.k.useHostCores && t.k.Platform.DetectsCPUPreemption()
 }
 
-// RSEQCriticalRegion returns a copy of t's thread group's current restartable
-// sequence.
-func (t *Task) RSEQCriticalRegion() RSEQCriticalRegion {
-	return *t.tg.rscr.Load().(*RSEQCriticalRegion)
+// SetRSeq registers addr as this thread's rseq structure.
+//
+// Preconditions: The caller must be running on the task goroutine.
+func (t *Task) SetRSeq(addr usermem.Addr, length, signature uint32) error {
+	if t.rseqAddr != 0 {
+		if t.rseqAddr != addr {
+			return syserror.EINVAL
+		}
+		if t.rseqSignature != signature {
+			return syserror.EINVAL
+		}
+		return syserror.EBUSY
+	}
+
+	// rseq must be aligned and correctly sized.
+	if addr&(linux.AlignOfRSeq-1) != 0 {
+		return syserror.EINVAL
+	}
+	if length != linux.SizeOfRSeq {
+		return syserror.EINVAL
+	}
+	if _, ok := t.MemoryManager().CheckIORange(addr, linux.SizeOfRSeq); !ok {
+		return syserror.EFAULT
+	}
+
+	t.rseqAddr = addr
+	t.rseqSignature = signature
+
+	// Initialize the CPUID.
+	//
+	// Linux implicitly does this on return from userspace, where failure
+	// would cause SIGSEGV.
+	if err := t.rseqUpdateCPU(); err != nil {
+		t.rseqAddr = 0
+		t.rseqSignature = 0
+
+		t.Debugf("Failed to copy CPU to %#x for rseq: %v", t.rseqAddr, err)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return syserror.EFAULT
+	}
+
+	return nil
 }
 
-// SetRSEQCriticalRegion replaces t's thread group's restartable sequence.
+// ClearRSeq unregisters addr as this thread's rseq structure.
 //
-// Preconditions: t.RSEQAvailable() == true.
-func (t *Task) SetRSEQCriticalRegion(rscr RSEQCriticalRegion) error {
+// Preconditions: The caller must be running on the task goroutine.
+func (t *Task) ClearRSeq(addr usermem.Addr, length, signature uint32) error {
+	if t.rseqAddr == 0 {
+		return syserror.EINVAL
+	}
+	if t.rseqAddr != addr {
+		return syserror.EINVAL
+	}
+	if length != linux.SizeOfRSeq {
+		return syserror.EINVAL
+	}
+	if t.rseqSignature != signature {
+		return syserror.EPERM
+	}
+
+	if err := t.rseqClearCPU(); err != nil {
+		return err
+	}
+
+	t.rseqAddr = 0
+	t.rseqSignature = 0
+
+	if t.oldRSeqCPUAddr == 0 {
+		// rseqCPU no longer needed.
+		t.rseqCPU = -1
+	}
+
+	return nil
+}
+
+// OldRSeqCriticalRegion returns a copy of t's thread group's current
+// old restartable sequence.
+func (t *Task) OldRSeqCriticalRegion() OldRSeqCriticalRegion {
+	return *t.tg.oldRSeqCritical.Load().(*OldRSeqCriticalRegion)
+}
+
+// SetOldRSeqCriticalRegion replaces t's thread group's old restartable
+// sequence.
+//
+// Preconditions: t.RSeqAvailable() == true.
+func (t *Task) SetOldRSeqCriticalRegion(r OldRSeqCriticalRegion) error {
 	// These checks are somewhat more lenient than in Linux, which (bizarrely)
-	// requires rscr.CriticalSection to be non-empty and rscr.Restart to be
-	// outside of rscr.CriticalSection, even if rscr.CriticalSection.Start == 0
+	// requires r.CriticalSection to be non-empty and r.Restart to be
+	// outside of r.CriticalSection, even if r.CriticalSection.Start == 0
 	// (which disables the critical region).
-	if rscr.CriticalSection.Start == 0 {
-		rscr.CriticalSection.End = 0
-		rscr.Restart = 0
-		t.tg.rscr.Store(&rscr)
+	if r.CriticalSection.Start == 0 {
+		r.CriticalSection.End = 0
+		r.Restart = 0
+		t.tg.oldRSeqCritical.Store(&r)
 		return nil
 	}
-	if rscr.CriticalSection.Start >= rscr.CriticalSection.End {
+	if r.CriticalSection.Start >= r.CriticalSection.End {
 		return syserror.EINVAL
 	}
-	if rscr.CriticalSection.Contains(rscr.Restart) {
+	if r.CriticalSection.Contains(r.Restart) {
 		return syserror.EINVAL
 	}
-	// TODO(jamieliu): check that rscr.CriticalSection and rscr.Restart are in
-	// the application address range, for consistency with Linux
-	t.tg.rscr.Store(&rscr)
+	// TODO(jamieliu): check that r.CriticalSection and r.Restart are in
+	// the application address range, for consistency with Linux.
+	t.tg.oldRSeqCritical.Store(&r)
 	return nil
 }
 
-// RSEQCPUAddr returns the address that RSEQ will keep updated with t's CPU
-// number.
+// OldRSeqCPUAddr returns the address that old rseq will keep updated with t's
+// CPU number.
 //
 // Preconditions: The caller must be running on the task goroutine.
-func (t *Task) RSEQCPUAddr() usermem.Addr {
-	return t.rseqCPUAddr
+func (t *Task) OldRSeqCPUAddr() usermem.Addr {
+	return t.oldRSeqCPUAddr
 }
 
-// SetRSEQCPUAddr replaces the address that RSEQ will keep updated with t's CPU
-// number.
+// SetOldRSeqCPUAddr replaces the address that old rseq will keep updated with
+// t's CPU number.
 //
-// Preconditions: t.RSEQAvailable() == true. The caller must be running on the
+// Preconditions: t.RSeqAvailable() == true. The caller must be running on the
 // task goroutine. t's AddressSpace must be active.
-func (t *Task) SetRSEQCPUAddr(addr usermem.Addr) error {
-	t.rseqCPUAddr = addr
-	if addr != 0 {
-		t.rseqCPU = int32(hostcpu.GetCPU())
-		if err := t.rseqCopyOutCPU(); err != nil {
-			t.rseqCPUAddr = 0
-			t.rseqCPU = -1
-			return syserror.EINVAL // yes, EINVAL, not err or EFAULT
-		}
-	} else {
-		t.rseqCPU = -1
+func (t *Task) SetOldRSeqCPUAddr(addr usermem.Addr) error {
+	t.oldRSeqCPUAddr = addr
+
+	// Check that addr is writable.
+	//
+	// N.B. rseqUpdateCPU may fail on a bad t.rseqAddr as well. That's
+	// unfortunate, but unlikely in a correct program.
+	if err := t.rseqUpdateCPU(); err != nil {
+		t.oldRSeqCPUAddr = 0
+		return syserror.EINVAL // yes, EINVAL, not err or EFAULT
 	}
 	return nil
 }
 
 // Preconditions: The caller must be running on the task goroutine. t's
 // AddressSpace must be active.
-func (t *Task) rseqCopyOutCPU() error {
+func (t *Task) rseqUpdateCPU() error {
+	if t.rseqAddr == 0 && t.oldRSeqCPUAddr == 0 {
+		t.rseqCPU = -1
+		return nil
+	}
+
+	t.rseqCPU = int32(hostcpu.GetCPU())
+
+	// Update both CPUs, even if one fails.
+	rerr := t.rseqCopyOutCPU()
+	oerr := t.oldRSeqCopyOutCPU()
+
+	if rerr != nil {
+		return rerr
+	}
+	return oerr
+}
+
+// Preconditions: The caller must be running on the task goroutine. t's
+// AddressSpace must be active.
+func (t *Task) oldRSeqCopyOutCPU() error {
+	if t.oldRSeqCPUAddr == 0 {
+		return nil
+	}
+
 	buf := t.CopyScratchBuffer(4)
 	usermem.ByteOrder.PutUint32(buf, uint32(t.rseqCPU))
-	_, err := t.CopyOutBytes(t.rseqCPUAddr, buf)
+	_, err := t.CopyOutBytes(t.oldRSeqCPUAddr, buf)
+	return err
+}
+
+// Preconditions: The caller must be running on the task goroutine. t's
+// AddressSpace must be active.
+func (t *Task) rseqCopyOutCPU() error {
+	if t.rseqAddr == 0 {
+		return nil
+	}
+
+	buf := t.CopyScratchBuffer(8)
+	// CPUIDStart and CPUID are the first two fields in linux.RSeq.
+	usermem.ByteOrder.PutUint32(buf, uint32(t.rseqCPU))     // CPUIDStart
+	usermem.ByteOrder.PutUint32(buf[4:], uint32(t.rseqCPU)) // CPUID
+	// N.B. This write is not atomic, but since this occurs on the task
+	// goroutine then as long as userspace uses a single-instruction read
+	// it can't see an invalid value.
+	_, err := t.CopyOutBytes(t.rseqAddr, buf)
+	return err
+}
+
+// Preconditions: The caller must be running on the task goroutine. t's
+// AddressSpace must be active.
+func (t *Task) rseqClearCPU() error {
+	buf := t.CopyScratchBuffer(8)
+	// CPUIDStart and CPUID are the first two fields in linux.RSeq.
+	usermem.ByteOrder.PutUint32(buf, 0)                                   // CPUIDStart
+	usermem.ByteOrder.PutUint32(buf[4:], linux.RSEQ_CPU_ID_UNINITIALIZED) // CPUID
+	// N.B. This write is not atomic, but since this occurs on the task
+	// goroutine then as long as userspace uses a single-instruction read
+	// it can't see an invalid value.
+	_, err := t.CopyOutBytes(t.rseqAddr, buf)
 	return err
 }
 
+// rseqAddrInterrupt checks if IP is in a critical section, and aborts if so.
+//
+// This is a bit complex since both the RSeq and RSeqCriticalSection structs
+// are stored in userspace. So we must:
+//
+// 1. Copy in the address of RSeqCriticalSection from RSeq.
+// 2. Copy in RSeqCriticalSection itself.
+// 3. Validate critical section struct version, address range, abort address.
+// 4. Validate the abort signature (4 bytes preceding abort IP match expected
+//    signature).
+// 5. Clear address of RSeqCriticalSection from RSeq.
+// 6. Finally, conditionally abort.
+//
+// See kernel/rseq.c:rseq_ip_fixup for reference.
+//
+// Preconditions: The caller must be running on the task goroutine. t's
+// AddressSpace must be active.
+func (t *Task) rseqAddrInterrupt() {
+	if t.rseqAddr == 0 {
+		return
+	}
+
+	critAddrAddr, ok := t.rseqAddr.AddLength(linux.OffsetOfRSeqCriticalSection)
+	if !ok {
+		// SetRSeq should validate this.
+		panic(fmt.Sprintf("t.rseqAddr (%#x) not large enough", t.rseqAddr))
+	}
+
+	if t.Arch().Width() != 8 {
+		// We only handle 64-bit for now.
+		t.Debugf("Only 64-bit rseq supported.")
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	buf := t.CopyScratchBuffer(8)
+	if _, err := t.CopyInBytes(critAddrAddr, buf); err != nil {
+		t.Debugf("Failed to copy critical section address from %#x for rseq: %v", critAddrAddr, err)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	critAddr := usermem.Addr(usermem.ByteOrder.Uint64(buf))
+	if critAddr == 0 {
+		return
+	}
+
+	buf = t.CopyScratchBuffer(linux.SizeOfRSeqCriticalSection)
+	if _, err := t.CopyInBytes(critAddr, buf); err != nil {
+		t.Debugf("Failed to copy critical section from %#x for rseq: %v", critAddr, err)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	// Manually marshal RSeqCriticalSection as this is in the hot path when
+	// rseq is enabled. It must be as fast as possible.
+	//
+	// TODO(b/130243041): Replace with go_marshal.
+	cs := linux.RSeqCriticalSection{
+		Version:          usermem.ByteOrder.Uint32(buf[0:4]),
+		Flags:            usermem.ByteOrder.Uint32(buf[4:8]),
+		Start:            usermem.ByteOrder.Uint64(buf[8:16]),
+		PostCommitOffset: usermem.ByteOrder.Uint64(buf[16:24]),
+		Abort:            usermem.ByteOrder.Uint64(buf[24:32]),
+	}
+
+	if cs.Version != 0 {
+		t.Debugf("Unknown version in %+v", cs)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	start := usermem.Addr(cs.Start)
+	critRange, ok := start.ToRange(cs.PostCommitOffset)
+	if !ok {
+		t.Debugf("Invalid start and offset in %+v", cs)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	abort := usermem.Addr(cs.Abort)
+	if critRange.Contains(abort) {
+		t.Debugf("Abort in critical section in %+v", cs)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	// Verify signature.
+	sigAddr := abort - linux.SizeOfRSeqSignature
+
+	buf = t.CopyScratchBuffer(linux.SizeOfRSeqSignature)
+	if _, err := t.CopyInBytes(sigAddr, buf); err != nil {
+		t.Debugf("Failed to copy critical section signature from %#x for rseq: %v", sigAddr, err)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	sig := usermem.ByteOrder.Uint32(buf)
+	if sig != t.rseqSignature {
+		t.Debugf("Mismatched rseq signature %d != %d", sig, t.rseqSignature)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	// Clear the critical section address.
+	//
+	// NOTE(b/143949567): We don't support any rseq flags, so we always
+	// restart if we are in the critical section, and thus *always* clear
+	// critAddrAddr.
+	if _, err := t.MemoryManager().ZeroOut(t, critAddrAddr, int64(t.Arch().Width()), usermem.IOOpts{
+		AddressSpaceActive: true,
+	}); err != nil {
+		t.Debugf("Failed to clear critical section address from %#x for rseq: %v", critAddrAddr, err)
+		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
+		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))
+		return
+	}
+
+	// Finally we can actually decide whether or not to restart.
+	if !critRange.Contains(usermem.Addr(t.Arch().IP())) {
+		return
+	}
+
+	t.Arch().SetIP(uintptr(cs.Abort))
+}
+
 // Preconditions: The caller must be running on the task goroutine.
-func (t *Task) rseqInterrupt() {
-	rscr := t.tg.rscr.Load().(*RSEQCriticalRegion)
-	if ip := t.Arch().IP(); rscr.CriticalSection.Contains(usermem.Addr(ip)) {
-		t.Debugf("Interrupted RSEQ critical section at %#x; restarting at %#x", ip, rscr.Restart)
-		t.Arch().SetIP(uintptr(rscr.Restart))
-		t.Arch().SetRSEQInterruptedIP(ip)
+func (t *Task) oldRSeqInterrupt() {
+	r := t.tg.oldRSeqCritical.Load().(*OldRSeqCriticalRegion)
+	if ip := t.Arch().IP(); r.CriticalSection.Contains(usermem.Addr(ip)) {
+		t.Debugf("Interrupted rseq critical section at %#x; restarting at %#x", ip, r.Restart)
+		t.Arch().SetIP(uintptr(r.Restart))
+		t.Arch().SetOldRSeqInterruptedIP(ip)
 	}
 }
+
+// Preconditions: The caller must be running on the task goroutine.
+func (t *Task) rseqInterrupt() {
+	t.rseqAddrInterrupt()
+	t.oldRSeqInterrupt()
+}