1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
|
// 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.
//go:build amd64
// +build amd64
package usertrap
import (
"encoding/binary"
"unsafe"
"gvisor.dev/gvisor/pkg/context"
"gvisor.dev/gvisor/pkg/marshal/primitive"
"gvisor.dev/gvisor/pkg/sentry/arch"
"gvisor.dev/gvisor/pkg/sentry/platform/systrap/sysmsg"
"gvisor.dev/gvisor/pkg/usermem"
)
// addTrapLocked constructs a trampoline for a specified syscall.
//
// mm.UserTrap.Lock has to be taken.
func (s *State) addTrapLocked(ctx context.Context, ac *arch.Context64, mm memoryManager, sysno uint32) (uint64, error) {
trapAddr, err := s.newTrapLocked(ctx, mm)
if err != nil {
return 0, err
}
// First eight bytes is an address which points to the 9th byte, they
// are used as an argument for the jmp instruction.
//
// Then here is the code of the syscall trampoline.
// First, we need to lock the sysmsg struct by setting StatePrep. This
// is used to synchronise with sighandler which uses the same struct
// sysmsg. And we need to guarantee that the current thread will not be
// interrupted in syshandler, because the sysmsg struct isn't saved on
// S/R.
// A thread stack can't be change, so the call instruction can't be
// used and we need to save values of stack and instruction registers,
// switch to the syshandler stack and call the jmp instruction to
// syshandler:
// mov sysmsg.ThreadStatePrep, %gs:offset(msg.State)
// mov %rsp,%gs:0x20 // msg.AppStack
// mov %gs:0x18,%rsp // msg.SyshandlerStack
// movabs $ret_addr, %rax
// mov %rax,%gs:0x8 // msg.RetAddr
// mov sysno,%eax
// jmpq *%gs:0x10 // msg.Syshandler
trap := []byte{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
// msg.State = sysmsg.ThreadStatePrep
/*08*/ 0x65, 0xc7, 0x04, 0x25, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov $X, %gs:OFFSET
/*20*/ 0x65, 0x48, 0x89, 0x24, 0x25, 0x20, 0x00, 0x00, 0x00, // mov %rsp,%gs:0x20
/*29*/ 0x65, 0x48, 0x8b, 0x24, 0x25, 0x18, 0x00, 0x00, 0x00, // mov %gs:0x18,%rsp
/*38*/ 0x48, 0xb8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // movabs $ret_addr, %rax
/*48*/ 0x65, 0x48, 0x89, 0x04, 0x25, 0x08, 0x00, 0x00, 0x00, // mov %rax,%gs:0x8
/*57*/ 0xb8, 0x00, 0x00, 0x00, 0x00, // mov sysno,%eax
/*62*/ 0x65, 0xff, 0x24, 0x25, 0x10, 0x00, 0x00, 0x00, // jmpq *%gs:0x10
}
binary.LittleEndian.PutUint64(trap[40:48], uint64(ac.IP()))
binary.LittleEndian.PutUint32(trap[58:62], sysno)
binary.LittleEndian.PutUint64(trap[:8], uint64(trapAddr)+8)
var msg *sysmsg.Msg
binary.LittleEndian.PutUint32(trap[12:16], uint32(unsafe.Offsetof(msg.State)))
binary.LittleEndian.PutUint32(trap[16:20], uint32(sysmsg.ThreadStatePrep))
binary.LittleEndian.PutUint32(trap[25:29], uint32(unsafe.Offsetof(msg.AppStack)))
binary.LittleEndian.PutUint32(trap[34:38], uint32(unsafe.Offsetof(msg.SyshandlerStack)))
binary.LittleEndian.PutUint32(trap[53:57], uint32(unsafe.Offsetof(msg.RetAddr)))
binary.LittleEndian.PutUint32(trap[66:70], uint32(unsafe.Offsetof(msg.Syshandler)))
iocc := usermem.IOCopyContext{
Ctx: ctx,
IO: mm,
Opts: usermem.IOOpts{
IgnorePermissions: true,
},
}
_, err = primitive.CopyByteSliceOut(&iocc, trapAddr, trap[:])
return uint64(trapAddr), err
}
|
