Merge pull request #6573 from avagin:kvm-seccomp-mmap

PiperOrigin-RevId: 398572735

15 files changed, 531 insertions, 81 deletions

diff --git a/pkg/sentry/platform/kvm/BUILD b/pkg/sentry/platform/kvm/BUILD
index 8a490b3de..a26f54269 100644
--- a/pkg/sentry/platform/kvm/BUILD
+++ b/pkg/sentry/platform/kvm/BUILD
@@ -1,13 +1,26 @@
 load("//tools:defs.bzl", "go_library", "go_test")
+load("//tools/go_generics:defs.bzl", "go_template_instance")
 
 package(licenses = ["notice"])
 
+go_template_instance(
+    name = "atomicptr_machine",
+    out = "atomicptr_machine_unsafe.go",
+    package = "kvm",
+    prefix = "machine",
+    template = "//pkg/sync/atomicptr:generic_atomicptr",
+    types = {
+        "Value": "machine",
+    },
+)
+
 go_library(
     name = "kvm",
     srcs = [
         "address_space.go",
         "address_space_amd64.go",
         "address_space_arm64.go",
+        "atomicptr_machine_unsafe.go",
         "bluepill.go",
         "bluepill_allocator.go",
         "bluepill_amd64.go",
@@ -69,10 +82,17 @@ go_test(
         "kvm_amd64_test.go",
         "kvm_amd64_test.s",
         "kvm_arm64_test.go",
+        "kvm_safecopy_test.go",
         "kvm_test.go",
         "virtual_map_test.go",
     ],
     library = ":kvm",
+    # FIXME(gvisor.dev/issue/3374): Not working with all build systems.
+    nogo = False,
+    # cgo has to be disabled. We have seen libc that blocks all signals and
+    # calls mmap from pthread_create, but we use SIGSYS to trap mmap system
+    # calls.
+    pure = True,
     tags = [
         "manual",
         "nogotsan",
@@ -81,8 +101,10 @@ go_test(
     deps = [
         "//pkg/abi/linux",
         "//pkg/hostarch",
+        "//pkg/memutil",
         "//pkg/ring0",
         "//pkg/ring0/pagetables",
+        "//pkg/safecopy",
         "//pkg/sentry/arch",
         "//pkg/sentry/arch/fpu",
         "//pkg/sentry/platform",
diff --git a/pkg/sentry/platform/kvm/bluepill.go b/pkg/sentry/platform/kvm/bluepill.go
index bb9967b9f..826997e77 100644
--- a/pkg/sentry/platform/kvm/bluepill.go
+++ b/pkg/sentry/platform/kvm/bluepill.go
@@ -61,6 +61,9 @@ var (
 	// This is called by bluepillHandler.
 	savedHandler uintptr
 
+	// savedSigsysHandler is a pointer to the previos handler of the SIGSYS signals.
+	savedSigsysHandler uintptr
+
 	// dieTrampolineAddr is the address of dieTrampoline.
 	dieTrampolineAddr uintptr
 )
diff --git a/pkg/sentry/platform/kvm/bluepill_amd64.s b/pkg/sentry/platform/kvm/bluepill_amd64.s
index c2a1dca11..5d8358f64 100644
--- a/pkg/sentry/platform/kvm/bluepill_amd64.s
+++ b/pkg/sentry/platform/kvm/bluepill_amd64.s
@@ -32,6 +32,8 @@
 // This is checked as the source of the fault.
 #define CLI $0xfa
 
+#define SYS_MMAP 9
+
 // See bluepill.go.
 TEXT ·bluepill(SB),NOSPLIT,$0
 begin:
@@ -95,6 +97,31 @@ TEXT ·addrOfSighandler(SB), $0-8
 	MOVQ AX, ret+0(FP)
 	RET
 
+TEXT ·sigsysHandler(SB),NOSPLIT,$0
+	// Check if the signal is from the kernel.
+	MOVQ $1, CX
+	CMPL CX, 0x8(SI)
+	JNE fallback
+
+	MOVL CONTEXT_RAX(DX), CX
+	CMPL CX, $SYS_MMAP
+	JNE fallback
+	PUSHQ DX                    // First argument (context).
+	CALL ·seccompMmapHandler(SB)    // Call the handler.
+	POPQ DX                     // Discard the argument.
+	RET
+fallback:
+	// Jump to the previous signal handler.
+	XORQ CX, CX
+	MOVQ ·savedSigsysHandler(SB), AX
+	JMP AX
+
+// func addrOfSighandler() uintptr
+TEXT ·addrOfSigsysHandler(SB), $0-8
+	MOVQ $·sigsysHandler(SB), AX
+	MOVQ AX, ret+0(FP)
+	RET
+
 // dieTrampoline: see bluepill.go, bluepill_amd64_unsafe.go for documentation.
 TEXT ·dieTrampoline(SB),NOSPLIT,$0
 	PUSHQ BX // First argument (vCPU).
diff --git a/pkg/sentry/platform/kvm/bluepill_arm64.s b/pkg/sentry/platform/kvm/bluepill_arm64.s
index 308f2a951..9690e3772 100644
--- a/pkg/sentry/platform/kvm/bluepill_arm64.s
+++ b/pkg/sentry/platform/kvm/bluepill_arm64.s
@@ -29,9 +29,12 @@
 // Only limited use of the context is done in the assembly stub below, most is
 // done in the Go handlers.
 #define SIGINFO_SIGNO 0x0
+#define SIGINFO_CODE 0x8
 #define CONTEXT_PC  0x1B8
 #define CONTEXT_R0 0xB8
 
+#define SYS_MMAP 222
+
 // getTLS returns the value of TPIDR_EL0 register.
 TEXT ·getTLS(SB),NOSPLIT,$0-8
 	MRS TPIDR_EL0, R1
@@ -98,6 +101,37 @@ TEXT ·addrOfSighandler(SB), $0-8
 	MOVD	R0, ret+0(FP)
 	RET
 
+// The arguments are the following:
+//
+// 	R0 - The signal number.
+// 	R1 - Pointer to siginfo_t structure.
+// 	R2 - Pointer to ucontext structure.
+//
+TEXT ·sigsysHandler(SB),NOSPLIT,$0
+	// si_code should be SYS_SECCOMP.
+	MOVD	SIGINFO_CODE(R1), R7
+	CMPW	$1, R7
+	BNE	fallback
+
+	CMPW	$SYS_MMAP, R8
+	BNE	fallback
+
+	MOVD	R2, 8(RSP)
+	BL	·seccompMmapHandler(SB)   // Call the handler.
+
+	RET
+
+fallback:
+	// Jump to the previous signal handler.
+	MOVD	·savedHandler(SB), R7
+	B	(R7)
+
+// func addrOfSighandler() uintptr
+TEXT ·addrOfSigsysHandler(SB), $0-8
+	MOVD	$·sigsysHandler(SB), R0
+	MOVD	R0, ret+0(FP)
+	RET
+
 // dieTrampoline: see bluepill.go, bluepill_arm64_unsafe.go for documentation.
 TEXT ·dieTrampoline(SB),NOSPLIT,$0
 	// R0: Fake the old PC as caller
diff --git a/pkg/sentry/platform/kvm/bluepill_unsafe.go b/pkg/sentry/platform/kvm/bluepill_unsafe.go
index 0f0c1e73b..e38ca05c0 100644
--- a/pkg/sentry/platform/kvm/bluepill_unsafe.go
+++ b/pkg/sentry/platform/kvm/bluepill_unsafe.go
@@ -193,36 +193,8 @@ func bluepillHandler(context unsafe.Pointer) {
 				return
 			}
 
-			// Increment the fault count.
-			atomic.AddUint32(&c.faults, 1)
-
-			// For MMIO, the physical address is the first data item.
-			physical = uintptr(c.runData.data[0])
-			virtual, ok := handleBluepillFault(c.machine, physical, physicalRegions, _KVM_MEM_FLAGS_NONE)
-			if !ok {
-				c.die(bluepillArchContext(context), "invalid physical address")
-				return
-			}
-
-			// We now need to fill in the data appropriately. KVM
-			// expects us to provide the result of the given MMIO
-			// operation in the runData struct. This is safe
-			// because, if a fault occurs here, the same fault
-			// would have occurred in guest mode. The kernel should
-			// not create invalid page table mappings.
-			data := (*[8]byte)(unsafe.Pointer(&c.runData.data[1]))
-			length := (uintptr)((uint32)(c.runData.data[2]))
-			write := (uint8)(((c.runData.data[2] >> 32) & 0xff)) != 0
-			for i := uintptr(0); i < length; i++ {
-				b := bytePtr(uintptr(virtual) + i)
-				if write {
-					// Write to the given address.
-					*b = data[i]
-				} else {
-					// Read from the given address.
-					data[i] = *b
-				}
-			}
+			c.die(bluepillArchContext(context), "exit_mmio")
+			return
 		case _KVM_EXIT_IRQ_WINDOW_OPEN:
 			bluepillStopGuest(c)
 		case _KVM_EXIT_SHUTDOWN:
diff --git a/pkg/sentry/platform/kvm/kvm_safecopy_test.go b/pkg/sentry/platform/kvm/kvm_safecopy_test.go
new file mode 100644
index 000000000..9a87c9e6f
--- /dev/null
+++ b/pkg/sentry/platform/kvm/kvm_safecopy_test.go
@@ -0,0 +1,104 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// FIXME(gvisor.dev/issue//6629): These tests don't pass on ARM64.
+//
+//go:build amd64
+// +build amd64
+
+package kvm
+
+import (
+	"fmt"
+	"os"
+	"testing"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/hostarch"
+	"gvisor.dev/gvisor/pkg/memutil"
+	"gvisor.dev/gvisor/pkg/safecopy"
+)
+
+func testSafecopy(t *testing.T, mapSize uintptr, fileSize uintptr, testFunc func(t *testing.T, c *vCPU, addr uintptr)) {
+	memfd, err := memutil.CreateMemFD(fmt.Sprintf("kvm_test_%d", os.Getpid()), 0)
+	if err != nil {
+		t.Errorf("error creating memfd: %v", err)
+	}
+
+	memfile := os.NewFile(uintptr(memfd), "kvm_test")
+	memfile.Truncate(int64(fileSize))
+	kvmTest(t, nil, func(c *vCPU) bool {
+		const n = 10
+		mappings := make([]uintptr, n)
+		defer func() {
+			for i := 0; i < n && mappings[i] != 0; i++ {
+				unix.RawSyscall(
+					unix.SYS_MUNMAP,
+					mappings[i], mapSize, 0)
+			}
+		}()
+		for i := 0; i < n; i++ {
+			addr, _, errno := unix.RawSyscall6(
+				unix.SYS_MMAP,
+				0,
+				mapSize,
+				unix.PROT_READ|unix.PROT_WRITE,
+				unix.MAP_SHARED|unix.MAP_FILE,
+				uintptr(memfile.Fd()),
+				0)
+			if errno != 0 {
+				t.Errorf("error mapping file: %v", errno)
+			}
+			mappings[i] = addr
+			testFunc(t, c, addr)
+		}
+		return false
+	})
+}
+
+func TestSafecopySigbus(t *testing.T) {
+	mapSize := uintptr(faultBlockSize)
+	fileSize := mapSize - hostarch.PageSize
+	buf := make([]byte, hostarch.PageSize)
+	testSafecopy(t, mapSize, fileSize, func(t *testing.T, c *vCPU, addr uintptr) {
+		want := safecopy.BusError{addr + fileSize}
+		bluepill(c)
+		_, err := safecopy.CopyIn(buf, unsafe.Pointer(addr+fileSize))
+		if err != want {
+			t.Errorf("expected error: got %v, want %v", err, want)
+		}
+	})
+}
+
+func TestSafecopy(t *testing.T) {
+	mapSize := uintptr(faultBlockSize)
+	fileSize := mapSize
+	testSafecopy(t, mapSize, fileSize, func(t *testing.T, c *vCPU, addr uintptr) {
+		want := uint32(0x12345678)
+		bluepill(c)
+		_, err := safecopy.SwapUint32(unsafe.Pointer(addr+fileSize-8), want)
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+		bluepill(c)
+		val, err := safecopy.LoadUint32(unsafe.Pointer(addr + fileSize - 8))
+		if err != nil {
+			t.Errorf("unexpected error: %v", err)
+		}
+		if val != want {
+			t.Errorf("incorrect value: got %x, want %x", val, want)
+		}
+	})
+}
diff --git a/pkg/sentry/platform/kvm/machine.go b/pkg/sentry/platform/kvm/machine.go
index d67563958..dcf34015d 100644
--- a/pkg/sentry/platform/kvm/machine.go
+++ b/pkg/sentry/platform/kvm/machine.go
@@ -17,15 +17,19 @@ package kvm
 import (
 	"fmt"
 	"runtime"
+	gosync "sync"
 	"sync/atomic"
 
 	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/atomicbitops"
 	"gvisor.dev/gvisor/pkg/hostarch"
 	"gvisor.dev/gvisor/pkg/log"
 	"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/sync"
 )
@@ -35,6 +39,9 @@ type machine struct {
 	// fd is the vm fd.
 	fd int
 
+	// machinePoolIndex is the index in the machinePool array.
+	machinePoolIndex uint32
+
 	// nextSlot is the next slot for setMemoryRegion.
 	//
 	// This must be accessed atomically. If nextSlot is ^uint32(0), then
@@ -192,6 +199,10 @@ func (m *machine) newVCPU() *vCPU {
 	return c // Done.
 }
 
+// readOnlyGuestRegions contains regions that have to be mapped read-only into
+// the guest physical address space. Right now, it is used on arm64 only.
+var readOnlyGuestRegions []region
+
 // newMachine returns a new VM context.
 func newMachine(vm int) (*machine, error) {
 	// Create the machine.
@@ -227,6 +238,10 @@ func newMachine(vm int) (*machine, error) {
 	m.upperSharedPageTables.MarkReadOnlyShared()
 	m.kernel.PageTables = pagetables.NewWithUpper(newAllocator(), m.upperSharedPageTables, ring0.KernelStartAddress)
 
+	// Install seccomp rules to trap runtime mmap system calls. They will
+	// be handled by seccompMmapHandler.
+	seccompMmapRules(m)
+
 	// Apply the physical mappings. Note that these mappings may point to
 	// guest physical addresses that are not actually available. These
 	// physical pages are mapped on demand, see kernel_unsafe.go.
@@ -241,32 +256,11 @@ func newMachine(vm int) (*machine, error) {
 		return true // Keep iterating.
 	})
 
-	var physicalRegionsReadOnly []physicalRegion
-	var physicalRegionsAvailable []physicalRegion
-
-	physicalRegionsReadOnly = rdonlyRegionsForSetMem()
-	physicalRegionsAvailable = availableRegionsForSetMem()
-
-	// Map all read-only regions.
-	for _, r := range physicalRegionsReadOnly {
-		m.mapPhysical(r.physical, r.length, physicalRegionsReadOnly, _KVM_MEM_READONLY)
-	}
-
 	// Ensure that the currently mapped virtual regions are actually
 	// available in the VM. Note that this doesn't guarantee no future
 	// faults, however it should guarantee that everything is available to
 	// ensure successful vCPU entry.
-	applyVirtualRegions(func(vr virtualRegion) {
-		if excludeVirtualRegion(vr) {
-			return // skip region.
-		}
-
-		for _, r := range physicalRegionsReadOnly {
-			if vr.virtual == r.virtual {
-				return
-			}
-		}
-
+	mapRegion := func(vr region, flags uint32) {
 		for virtual := vr.virtual; virtual < vr.virtual+vr.length; {
 			physical, length, ok := translateToPhysical(virtual)
 			if !ok {
@@ -280,9 +274,32 @@ func newMachine(vm int) (*machine, error) {
 			}
 
 			// Ensure the physical range is mapped.
-			m.mapPhysical(physical, length, physicalRegionsAvailable, _KVM_MEM_FLAGS_NONE)
+			m.mapPhysical(physical, length, physicalRegions, flags)
 			virtual += length
 		}
+	}
+
+	for _, vr := range readOnlyGuestRegions {
+		mapRegion(vr, _KVM_MEM_READONLY)
+	}
+
+	applyVirtualRegions(func(vr virtualRegion) {
+		if excludeVirtualRegion(vr) {
+			return // skip region.
+		}
+		for _, r := range readOnlyGuestRegions {
+			if vr.virtual == r.virtual {
+				return
+			}
+		}
+		// Take into account that the stack can grow down.
+		if vr.filename == "[stack]" {
+			vr.virtual -= 1 << 20
+			vr.length += 1 << 20
+		}
+
+		mapRegion(vr.region, 0)
+
 	})
 
 	// Initialize architecture state.
@@ -352,6 +369,10 @@ func (m *machine) mapPhysical(physical, length uintptr, phyRegions []physicalReg
 func (m *machine) Destroy() {
 	runtime.SetFinalizer(m, nil)
 
+	machinePoolMu.Lock()
+	machinePool[m.machinePoolIndex].Store(nil)
+	machinePoolMu.Unlock()
+
 	// Destroy vCPUs.
 	for _, c := range m.vCPUsByID {
 		if c == nil {
@@ -683,3 +704,72 @@ func (c *vCPU) setSystemTimeLegacy() error {
 		}
 	}
 }
+
+const machinePoolSize = 16
+
+// machinePool is enumerated from the seccompMmapHandler signal handler
+var (
+	machinePool          [machinePoolSize]machineAtomicPtr
+	machinePoolLen       uint32
+	machinePoolMu        sync.Mutex
+	seccompMmapRulesOnce gosync.Once
+)
+
+func sigsysHandler()
+func addrOfSigsysHandler() uintptr
+
+// seccompMmapRules adds seccomp rules to trap mmap system calls that will be
+// handled in seccompMmapHandler.
+func seccompMmapRules(m *machine) {
+	seccompMmapRulesOnce.Do(func() {
+		// Install the handler.
+		if err := safecopy.ReplaceSignalHandler(unix.SIGSYS, addrOfSigsysHandler(), &savedSigsysHandler); err != nil {
+			panic(fmt.Sprintf("Unable to set handler for signal %d: %v", bluepillSignal, err))
+		}
+		rules := []seccomp.RuleSet{}
+		rules = append(rules, []seccomp.RuleSet{
+			// Trap mmap system calls and handle them in sigsysGoHandler
+			{
+				Rules: seccomp.SyscallRules{
+					unix.SYS_MMAP: {
+						{
+							seccomp.MatchAny{},
+							seccomp.MatchAny{},
+							seccomp.MatchAny{},
+							/* MAP_DENYWRITE is ignored and used only for filtering. */
+							seccomp.MaskedEqual(unix.MAP_DENYWRITE, 0),
+						},
+					},
+				},
+				Action: linux.SECCOMP_RET_TRAP,
+			},
+		}...)
+		instrs, err := seccomp.BuildProgram(rules, linux.SECCOMP_RET_ALLOW, linux.SECCOMP_RET_ALLOW)
+		if err != nil {
+			panic(fmt.Sprintf("failed to build rules: %v", err))
+		}
+		// Perform the actual installation.
+		if err := seccomp.SetFilter(instrs); err != nil {
+			panic(fmt.Sprintf("failed to set filter: %v", err))
+		}
+	})
+
+	machinePoolMu.Lock()
+	n := atomic.LoadUint32(&machinePoolLen)
+	i := uint32(0)
+	for ; i < n; i++ {
+		if machinePool[i].Load() == nil {
+			break
+		}
+	}
+	if i == n {
+		if i == machinePoolSize {
+			machinePoolMu.Unlock()
+			panic("machinePool is full")
+		}
+		atomic.AddUint32(&machinePoolLen, 1)
+	}
+	machinePool[i].Store(m)
+	m.machinePoolIndex = i
+	machinePoolMu.Unlock()
+}
diff --git a/pkg/sentry/platform/kvm/machine_amd64.go b/pkg/sentry/platform/kvm/machine_amd64.go
index a96634381..ab1e036b7 100644
--- a/pkg/sentry/platform/kvm/machine_amd64.go
+++ b/pkg/sentry/platform/kvm/machine_amd64.go
@@ -309,22 +309,6 @@ func loadByte(ptr *byte) byte {
 	return *ptr
 }
 
-// prefaultFloatingPointState touches each page of the floating point state to
-// be sure that its physical pages are mapped.
-//
-// Otherwise the kernel can trigger KVM_EXIT_MMIO and an instruction that
-// triggered a fault will be emulated by the kvm kernel code, but it can't
-// emulate instructions like xsave and xrstor.
-//
-//go:nosplit
-func prefaultFloatingPointState(data *fpu.State) {
-	size := len(*data)
-	for i := 0; i < size; i += hostarch.PageSize {
-		loadByte(&(*data)[i])
-	}
-	loadByte(&(*data)[size-1])
-}
-
 // SwitchToUser unpacks architectural-details.
 func (c *vCPU) SwitchToUser(switchOpts ring0.SwitchOpts, info *linux.SignalInfo) (hostarch.AccessType, error) {
 	// Check for canonical addresses.
@@ -355,11 +339,6 @@ func (c *vCPU) SwitchToUser(switchOpts ring0.SwitchOpts, info *linux.SignalInfo)
 	// allocations occur.
 	entersyscall()
 	bluepill(c)
-	// The root table physical page has to be mapped to not fault in iret
-	// or sysret after switching into a user address space.  sysret and
-	// iret are in the upper half that is global and already mapped.
-	switchOpts.PageTables.PrefaultRootTable()
-	prefaultFloatingPointState(switchOpts.FloatingPointState)
 	vector = c.CPU.SwitchToUser(switchOpts)
 	exitsyscall()
 
@@ -522,3 +501,7 @@ func (m *machine) getNewVCPU() *vCPU {
 	}
 	return nil
 }
+
+func archPhysicalRegions(physicalRegions []physicalRegion) []physicalRegion {
+	return physicalRegions
+}
diff --git a/pkg/sentry/platform/kvm/machine_amd64_unsafe.go b/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
index de798bb2c..fbacea9ad 100644
--- a/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_amd64_unsafe.go
@@ -161,3 +161,15 @@ func (c *vCPU) getSystemRegisters(sregs *systemRegs) unix.Errno {
 	}
 	return 0
 }
+
+//go:nosplit
+func seccompMmapSyscall(context unsafe.Pointer) (uintptr, uintptr, unix.Errno) {
+	ctx := bluepillArchContext(context)
+
+	// MAP_DENYWRITE is deprecated and ignored by kernel. We use it only for seccomp filters.
+	addr, _, e := unix.RawSyscall6(uintptr(ctx.Rax), uintptr(ctx.Rdi), uintptr(ctx.Rsi),
+		uintptr(ctx.Rdx), uintptr(ctx.R10)|unix.MAP_DENYWRITE, uintptr(ctx.R8), uintptr(ctx.R9))
+	ctx.Rax = uint64(addr)
+
+	return addr, uintptr(ctx.Rsi), e
+}
diff --git a/pkg/sentry/platform/kvm/machine_arm64.go b/pkg/sentry/platform/kvm/machine_arm64.go
index 7937a8481..08d98c479 100644
--- a/pkg/sentry/platform/kvm/machine_arm64.go
+++ b/pkg/sentry/platform/kvm/machine_arm64.go
@@ -110,18 +110,128 @@ func rdonlyRegionsForSetMem() (phyRegions []physicalRegion) {
 	return phyRegions
 }
 
+// archPhysicalRegions fills readOnlyGuestRegions and allocates separate
+// physical regions form them.
+func archPhysicalRegions(physicalRegions []physicalRegion) []physicalRegion {
+	applyVirtualRegions(func(vr virtualRegion) {
+		if excludeVirtualRegion(vr) {
+			return // skip region.
+		}
+		if !vr.accessType.Write {
+			readOnlyGuestRegions = append(readOnlyGuestRegions, vr.region)
+		}
+	})
+
+	rdRegions := readOnlyGuestRegions[:]
+
+	// Add an unreachable region.
+	rdRegions = append(rdRegions, region{
+		virtual: 0xffffffffffffffff,
+		length:  0,
+	})
+
+	var regions []physicalRegion
+	addValidRegion := func(r *physicalRegion, virtual, length uintptr) {
+		if length == 0 {
+			return
+		}
+		regions = append(regions, physicalRegion{
+			region: region{
+				virtual: virtual,
+				length:  length,
+			},
+			physical: r.physical + (virtual - r.virtual),
+		})
+	}
+	i := 0
+	for _, pr := range physicalRegions {
+		start := pr.virtual
+		end := pr.virtual + pr.length
+		for start < end {
+			rdRegion := rdRegions[i]
+			rdStart := rdRegion.virtual
+			rdEnd := rdRegion.virtual + rdRegion.length
+			if rdEnd <= start {
+				i++
+				continue
+			}
+			if rdStart > start {
+				newEnd := rdStart
+				if end < rdStart {
+					newEnd = end
+				}
+				addValidRegion(&pr, start, newEnd-start)
+				start = rdStart
+				continue
+			}
+			if rdEnd < end {
+				addValidRegion(&pr, start, rdEnd-start)
+				start = rdEnd
+				continue
+			}
+			addValidRegion(&pr, start, end-start)
+			start = end
+		}
+	}
+
+	return regions
+}
+
 // Get all available physicalRegions.
-func availableRegionsForSetMem() (phyRegions []physicalRegion) {
-	var excludeRegions []region
+func availableRegionsForSetMem() []physicalRegion {
+	var excludedRegions []region
 	applyVirtualRegions(func(vr virtualRegion) {
 		if !vr.accessType.Write {
-			excludeRegions = append(excludeRegions, vr.region)
+			excludedRegions = append(excludedRegions, vr.region)
 		}
 	})
 
-	phyRegions = computePhysicalRegions(excludeRegions)
+	// Add an unreachable region.
+	excludedRegions = append(excludedRegions, region{
+		virtual: 0xffffffffffffffff,
+		length:  0,
+	})
 
-	return phyRegions
+	var regions []physicalRegion
+	addValidRegion := func(r *physicalRegion, virtual, length uintptr) {
+		if length == 0 {
+			return
+		}
+		regions = append(regions, physicalRegion{
+			region: region{
+				virtual: virtual,
+				length:  length,
+			},
+			physical: r.physical + (virtual - r.virtual),
+		})
+	}
+	i := 0
+	for _, pr := range physicalRegions {
+		start := pr.virtual
+		end := pr.virtual + pr.length
+		for start < end {
+			er := excludedRegions[i]
+			excludeEnd := er.virtual + er.length
+			excludeStart := er.virtual
+			if excludeEnd < start {
+				i++
+				continue
+			}
+			if excludeStart < start {
+				start = excludeEnd
+				i++
+				continue
+			}
+			rend := excludeStart
+			if rend > end {
+				rend = end
+			}
+			addValidRegion(&pr, start, rend-start)
+			start = excludeEnd
+		}
+	}
+
+	return regions
 }
 
 // nonCanonical generates a canonical address return.
diff --git a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
index 1a4a9ce7d..7e8e19dcb 100644
--- a/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_arm64_unsafe.go
@@ -333,3 +333,15 @@ func (c *vCPU) SwitchToUser(switchOpts ring0.SwitchOpts, info *linux.SignalInfo)
 	}
 
 }
+
+//go:nosplit
+func seccompMmapSyscall(context unsafe.Pointer) (uintptr, uintptr, unix.Errno) {
+	ctx := bluepillArchContext(context)
+
+	// MAP_DENYWRITE is deprecated and ignored by kernel. We use it only for seccomp filters.
+	addr, _, e := unix.RawSyscall6(uintptr(ctx.Regs[8]), uintptr(ctx.Regs[0]), uintptr(ctx.Regs[1]),
+		uintptr(ctx.Regs[2]), uintptr(ctx.Regs[3])|unix.MAP_DENYWRITE, uintptr(ctx.Regs[4]), uintptr(ctx.Regs[5]))
+	ctx.Regs[0] = uint64(addr)
+
+	return addr, uintptr(ctx.Regs[1]), e
+}
diff --git a/pkg/sentry/platform/kvm/machine_unsafe.go b/pkg/sentry/platform/kvm/machine_unsafe.go
index cc3a1253b..cf3a4e7c9 100644
--- a/pkg/sentry/platform/kvm/machine_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_unsafe.go
@@ -171,3 +171,46 @@ func (c *vCPU) setSignalMask() error {
 
 	return nil
 }
+
+// seccompMmapHandler is a signal handler for runtime mmap system calls
+// that are trapped by seccomp.
+//
+// It executes the mmap syscall with specified arguments and maps a new region
+// to the guest.
+//
+//go:nosplit
+func seccompMmapHandler(context unsafe.Pointer) {
+	addr, length, errno := seccompMmapSyscall(context)
+	if errno != 0 {
+		return
+	}
+
+	for i := uint32(0); i < atomic.LoadUint32(&machinePoolLen); i++ {
+		m := machinePool[i].Load()
+		if m == nil {
+			continue
+		}
+
+		// Map the new region to the guest.
+		vr := region{
+			virtual: addr,
+			length:  length,
+		}
+		for virtual := vr.virtual; virtual < vr.virtual+vr.length; {
+			physical, length, ok := translateToPhysical(virtual)
+			if !ok {
+				// This must be an invalid region that was
+				// knocked out by creation of the physical map.
+				return
+			}
+			if virtual+length > vr.virtual+vr.length {
+				// Cap the length to the end of the area.
+				length = vr.virtual + vr.length - virtual
+			}
+
+			// Ensure the physical range is mapped.
+			m.mapPhysical(physical, length, physicalRegions, _KVM_MEM_FLAGS_NONE)
+			virtual += length
+		}
+	}
+}
diff --git a/pkg/sentry/platform/kvm/physical_map.go b/pkg/sentry/platform/kvm/physical_map.go
index d812e6c26..9864d1258 100644
--- a/pkg/sentry/platform/kvm/physical_map.go
+++ b/pkg/sentry/platform/kvm/physical_map.go
@@ -168,6 +168,9 @@ func computePhysicalRegions(excludedRegions []region) (physicalRegions []physica
 	}
 	addValidRegion(lastExcludedEnd, ring0.MaximumUserAddress-lastExcludedEnd)
 
+	// Do arch-specific actions on physical regions.
+	physicalRegions = archPhysicalRegions(physicalRegions)
+
 	// Dump our all physical regions.
 	for _, r := range physicalRegions {
 		log.Infof("physicalRegion: virtual [%x,%x) => physical [%x,%x)",
diff --git a/pkg/sentry/platform/kvm/testutil/testutil_arm64.go b/pkg/sentry/platform/kvm/testutil/testutil_arm64.go
index 6d0ba8252..346a10043 100644
--- a/pkg/sentry/platform/kvm/testutil/testutil_arm64.go
+++ b/pkg/sentry/platform/kvm/testutil/testutil_arm64.go
@@ -30,8 +30,8 @@ import (
 func TLSWorks() bool
 
 // SetTestTarget sets the rip appropriately.
-func SetTestTarget(regs *arch.Registers, fn func()) {
-	regs.Pc = uint64(reflect.ValueOf(fn).Pointer())
+func SetTestTarget(regs *arch.Registers, fn uintptr) {
+	regs.Pc = uint64(fn)
 }
 
 // SetTouchTarget sets rax appropriately.
diff --git a/pkg/sentry/platform/kvm/testutil/testutil_arm64.s b/pkg/sentry/platform/kvm/testutil/testutil_arm64.s
index 7348c29a5..42876245a 100644
--- a/pkg/sentry/platform/kvm/testutil/testutil_arm64.s
+++ b/pkg/sentry/platform/kvm/testutil/testutil_arm64.s
@@ -28,6 +28,11 @@ TEXT ·Getpid(SB),NOSPLIT,$0
 	SVC
 	RET
 
+TEXT ·AddrOfGetpid(SB),NOSPLIT,$0-8
+	MOVD $·Getpid(SB), R0
+	MOVD R0, ret+0(FP)
+	RET
+
 TEXT ·Touch(SB),NOSPLIT,$0
 start:
 	MOVD 0(R8), R1
@@ -35,21 +40,41 @@ start:
 	SVC
 	B start
 
+TEXT ·AddrOfTouch(SB),NOSPLIT,$0-8
+	MOVD $·Touch(SB), R0
+	MOVD R0, ret+0(FP)
+	RET
+
 TEXT ·HaltLoop(SB),NOSPLIT,$0
 start:
 	HLT
 	B start
 
+TEXT ·AddOfHaltLoop(SB),NOSPLIT,$0-8
+	MOVD $·HaltLoop(SB), R0
+	MOVD R0, ret+0(FP)
+	RET
+
 // This function simulates a loop of syscall.
 TEXT ·SyscallLoop(SB),NOSPLIT,$0
 start:
 	SVC
 	B start
 
+TEXT ·AddrOfSyscallLoop(SB),NOSPLIT,$0-8
+	MOVD $·SyscallLoop(SB), R0
+	MOVD R0, ret+0(FP)
+	RET
+
 TEXT ·SpinLoop(SB),NOSPLIT,$0
 start:
 	B start
 
+TEXT ·AddrOfSpinLoop(SB),NOSPLIT,$0-8
+	MOVD $·SpinLoop(SB), R0
+	MOVD R0, ret+0(FP)
+	RET
+
 TEXT ·TLSWorks(SB),NOSPLIT,$0-8
         NO_LOCAL_POINTERS
         MOVD $0x6789, R5
@@ -125,6 +150,11 @@ TEXT ·TwiddleRegsSyscall(SB),NOSPLIT,$0
 	SVC
 	RET // never reached
 
+TEXT ·AddrOfTwiddleRegsSyscall(SB),NOSPLIT,$0-8
+	MOVD $·TwiddleRegsSyscall(SB), R0
+	MOVD R0, ret+0(FP)
+	RET
+
 TEXT ·TwiddleRegsFault(SB),NOSPLIT,$0
 	TWIDDLE_REGS()
 	MSR R10, TPIDR_EL0
@@ -132,3 +162,8 @@ TEXT ·TwiddleRegsFault(SB),NOSPLIT,$0
 	// Branch to Register branches unconditionally to an address in <Rn>.
 	JMP (R6) // <=> br x6, must fault
 	RET // never reached
+
+TEXT ·AddrOfTwiddleRegsFault(SB),NOSPLIT,$0-8
+	MOVD $·TwiddleRegsFault(SB), R0
+	MOVD R0, ret+0(FP)
+	RET