Better strace logging for epoll syscalls.

Example:

epoll_ctl(0x3 anon_inode:[eventpoll], EPOLL_CTL_ADD, 0x6 anon_inode:[eventfd], 0x7efe2fd92a80 {events=EPOLLIN|EPOLLOUT data=0x10203040506070a}) = 0x0 (4.411µs)

epoll_wait(0x3 anon_inode:[eventpoll], 0x7efe2fd92b50 {{events=EPOLLOUT data=0x102030405060708}{events=EPOLLOUT data=0x102030405060708}{events=EPOLLOUT data=0x102030405060708}}, 0x3, 0xffffffff) = 0x3 (29.891µs)

PiperOrigin-RevId: 296258146

7 files changed, 120 insertions, 5 deletions

diff --git a/pkg/abi/linux/epoll.go b/pkg/abi/linux/epoll.go
index 6e4de69da..1121a1a92 100644
--- a/pkg/abi/linux/epoll.go
+++ b/pkg/abi/linux/epoll.go
@@ -14,6 +14,10 @@
 
 package linux
 
+import (
+	"gvisor.dev/gvisor/pkg/binary"
+)
+
 // Event masks.
 const (
 	EPOLLIN     = 0x1
@@ -53,3 +57,6 @@ const (
 	EPOLL_CTL_DEL = 0x2
 	EPOLL_CTL_MOD = 0x3
 )
+
+// SizeOfEpollEvent is the size of EpollEvent struct.
+var SizeOfEpollEvent = int(binary.Size(EpollEvent{}))
diff --git a/pkg/sentry/strace/BUILD b/pkg/sentry/strace/BUILD
index 2f39a6f2b..88d5db9fc 100644
--- a/pkg/sentry/strace/BUILD
+++ b/pkg/sentry/strace/BUILD
@@ -7,6 +7,7 @@ go_library(
     srcs = [
         "capability.go",
         "clone.go",
+        "epoll.go",
         "futex.go",
         "linux64_amd64.go",
         "linux64_arm64.go",
diff --git a/pkg/sentry/strace/epoll.go b/pkg/sentry/strace/epoll.go
new file mode 100644
index 000000000..a6e48b836
--- /dev/null
+++ b/pkg/sentry/strace/epoll.go
@@ -0,0 +1,89 @@
+// Copyright 2020 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.
+
+package strace
+
+import (
+	"fmt"
+	"strings"
+
+	"gvisor.dev/gvisor/pkg/abi"
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+func epollEvent(t *kernel.Task, eventAddr usermem.Addr) string {
+	var e linux.EpollEvent
+	if _, err := t.CopyIn(eventAddr, &e); err != nil {
+		return fmt.Sprintf("%#x {error reading event: %v}", eventAddr, err)
+	}
+	var sb strings.Builder
+	fmt.Fprintf(&sb, "%#x ", eventAddr)
+	writeEpollEvent(&sb, e)
+	return sb.String()
+}
+
+func epollEvents(t *kernel.Task, eventsAddr usermem.Addr, numEvents, maxBytes uint64) string {
+	var sb strings.Builder
+	fmt.Fprintf(&sb, "%#x {", eventsAddr)
+	addr := eventsAddr
+	for i := uint64(0); i < numEvents; i++ {
+		var e linux.EpollEvent
+		if _, err := t.CopyIn(addr, &e); err != nil {
+			fmt.Fprintf(&sb, "{error reading event at %#x: %v}", addr, err)
+			continue
+		}
+		writeEpollEvent(&sb, e)
+		if uint64(sb.Len()) >= maxBytes {
+			sb.WriteString("...")
+			break
+		}
+		if _, ok := addr.AddLength(uint64(linux.SizeOfEpollEvent)); !ok {
+			fmt.Fprintf(&sb, "{error reading event at %#x: EFAULT}", addr)
+			continue
+		}
+	}
+	sb.WriteString("}")
+	return sb.String()
+}
+
+func writeEpollEvent(sb *strings.Builder, e linux.EpollEvent) {
+	events := epollEventEvents.Parse(uint64(e.Events))
+	fmt.Fprintf(sb, "{events=%s data=[%#x, %#x]}", events, e.Data[0], e.Data[1])
+}
+
+var epollCtlOps = abi.ValueSet{
+	linux.EPOLL_CTL_ADD: "EPOLL_CTL_ADD",
+	linux.EPOLL_CTL_DEL: "EPOLL_CTL_DEL",
+	linux.EPOLL_CTL_MOD: "EPOLL_CTL_MOD",
+}
+
+var epollEventEvents = abi.FlagSet{
+	{Flag: linux.EPOLLIN, Name: "EPOLLIN"},
+	{Flag: linux.EPOLLPRI, Name: "EPOLLPRI"},
+	{Flag: linux.EPOLLOUT, Name: "EPOLLOUT"},
+	{Flag: linux.EPOLLERR, Name: "EPOLLERR"},
+	{Flag: linux.EPOLLHUP, Name: "EPULLHUP"},
+	{Flag: linux.EPOLLRDNORM, Name: "EPOLLRDNORM"},
+	{Flag: linux.EPOLLRDBAND, Name: "EPOLLRDBAND"},
+	{Flag: linux.EPOLLWRNORM, Name: "EPOLLWRNORM"},
+	{Flag: linux.EPOLLWRBAND, Name: "EPOLLWRBAND"},
+	{Flag: linux.EPOLLMSG, Name: "EPOLLMSG"},
+	{Flag: linux.EPOLLRDHUP, Name: "EPOLLRDHUP"},
+	{Flag: linux.EPOLLEXCLUSIVE, Name: "EPOLLEXCLUSIVE"},
+	{Flag: linux.EPOLLWAKEUP, Name: "EPOLLWAKEUP"},
+	{Flag: linux.EPOLLONESHOT, Name: "EPOLLONESHOT"},
+	{Flag: linux.EPOLLET, Name: "EPOLLET"},
+}
diff --git a/pkg/sentry/strace/linux64_amd64.go b/pkg/sentry/strace/linux64_amd64.go
index a4de545e9..71b92eaee 100644
--- a/pkg/sentry/strace/linux64_amd64.go
+++ b/pkg/sentry/strace/linux64_amd64.go
@@ -256,8 +256,8 @@ var linuxAMD64 = SyscallMap{
 	229: makeSyscallInfo("clock_getres", Hex, PostTimespec),
 	230: makeSyscallInfo("clock_nanosleep", Hex, Hex, Timespec, PostTimespec),
 	231: makeSyscallInfo("exit_group", Hex),
-	232: makeSyscallInfo("epoll_wait", Hex, Hex, Hex, Hex),
-	233: makeSyscallInfo("epoll_ctl", Hex, Hex, FD, Hex),
+	232: makeSyscallInfo("epoll_wait", FD, EpollEvents, Hex, Hex),
+	233: makeSyscallInfo("epoll_ctl", FD, EpollCtlOp, FD, EpollEvent),
 	234: makeSyscallInfo("tgkill", Hex, Hex, Signal),
 	235: makeSyscallInfo("utimes", Path, Timeval),
 	// 236: vserver (not implemented in the Linux kernel)
@@ -305,7 +305,7 @@ var linuxAMD64 = SyscallMap{
 	278: makeSyscallInfo("vmsplice", FD, Hex, Hex, Hex),
 	279: makeSyscallInfo("move_pages", Hex, Hex, Hex, Hex, Hex, Hex),
 	280: makeSyscallInfo("utimensat", FD, Path, UTimeTimespec, Hex),
-	281: makeSyscallInfo("epoll_pwait", Hex, Hex, Hex, Hex, SigSet, Hex),
+	281: makeSyscallInfo("epoll_pwait", FD, EpollEvents, Hex, Hex, SigSet, Hex),
 	282: makeSyscallInfo("signalfd", Hex, Hex, Hex),
 	283: makeSyscallInfo("timerfd_create", Hex, Hex),
 	284: makeSyscallInfo("eventfd", Hex),
diff --git a/pkg/sentry/strace/linux64_arm64.go b/pkg/sentry/strace/linux64_arm64.go
index 8bc38545f..bd7361a52 100644
--- a/pkg/sentry/strace/linux64_arm64.go
+++ b/pkg/sentry/strace/linux64_arm64.go
@@ -45,8 +45,8 @@ var linuxARM64 = SyscallMap{
 	18:  makeSyscallInfo("lookup_dcookie", Hex, Hex, Hex),
 	19:  makeSyscallInfo("eventfd2", Hex, Hex),
 	20:  makeSyscallInfo("epoll_create1", Hex),
-	21:  makeSyscallInfo("epoll_ctl", Hex, Hex, FD, Hex),
-	22:  makeSyscallInfo("epoll_pwait", Hex, Hex, Hex, Hex, SigSet, Hex),
+	21:  makeSyscallInfo("epoll_ctl", FD, EpollCtlOp, FD, EpollEvent),
+	22:  makeSyscallInfo("epoll_pwait", FD, EpollEvents, Hex, Hex, SigSet, Hex),
 	23:  makeSyscallInfo("dup", FD),
 	24:  makeSyscallInfo("dup3", FD, FD, Hex),
 	25:  makeSyscallInfo("fcntl", FD, Hex, Hex),
diff --git a/pkg/sentry/strace/strace.go b/pkg/sentry/strace/strace.go
index 46cb2a1cc..77655558e 100644
--- a/pkg/sentry/strace/strace.go
+++ b/pkg/sentry/strace/strace.go
@@ -481,6 +481,12 @@ func (i *SyscallInfo) pre(t *kernel.Task, args arch.SyscallArguments, maximumBlo
 			output = append(output, capData(t, args[arg-1].Pointer(), args[arg].Pointer()))
 		case PollFDs:
 			output = append(output, pollFDs(t, args[arg].Pointer(), uint(args[arg+1].Uint()), false))
+		case EpollCtlOp:
+			output = append(output, epollCtlOps.Parse(uint64(args[arg].Int())))
+		case EpollEvent:
+			output = append(output, epollEvent(t, args[arg].Pointer()))
+		case EpollEvents:
+			output = append(output, epollEvents(t, args[arg].Pointer(), 0 /* numEvents */, uint64(maximumBlobSize)))
 		case SelectFDSet:
 			output = append(output, fdSet(t, int(args[0].Int()), args[arg].Pointer()))
 		case Oct:
@@ -549,6 +555,8 @@ func (i *SyscallInfo) post(t *kernel.Task, args arch.SyscallArguments, rval uint
 			output[arg] = capData(t, args[arg-1].Pointer(), args[arg].Pointer())
 		case PollFDs:
 			output[arg] = pollFDs(t, args[arg].Pointer(), uint(args[arg+1].Uint()), true)
+		case EpollEvents:
+			output[arg] = epollEvents(t, args[arg].Pointer(), uint64(rval), uint64(maximumBlobSize))
 		case GetSockOptVal:
 			output[arg] = getSockOptVal(t, args[arg-2].Uint64() /* level */, args[arg-1].Uint64() /* optName */, args[arg].Pointer() /* optVal */, args[arg+1].Pointer() /* optLen */, maximumBlobSize, rval)
 		case SetSockOptVal:
diff --git a/pkg/sentry/strace/syscalls.go b/pkg/sentry/strace/syscalls.go
index 446d1e0f6..7e69b9279 100644
--- a/pkg/sentry/strace/syscalls.go
+++ b/pkg/sentry/strace/syscalls.go
@@ -228,6 +228,16 @@ const (
 	// SockOptLevel is the optname argument in getsockopt(2) and
 	// setsockopt(2).
 	SockOptName
+
+	// EpollCtlOp is the op argument to epoll_ctl(2).
+	EpollCtlOp
+
+	// EpollEvent is the event argument in epoll_ctl(2).
+	EpollEvent
+
+	// EpollEvents is an array of struct epoll_event. It is the events
+	// argument in epoll_wait(2)/epoll_pwait(2).
+	EpollEvents
 )
 
 // defaultFormat is the syscall argument format to use if the actual format is