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// Copyright 2018 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 seccomp
import (
"fmt"
"golang.org/x/sys/unix"
)
// The offsets are based on the following struct in include/linux/seccomp.h.
//
// struct seccomp_data {
// int nr;
// __u32 arch;
// __u64 instruction_pointer;
// __u64 args[6];
// };
const (
seccompDataOffsetNR = 0
seccompDataOffsetArch = 4
seccompDataOffsetIPLow = 8
seccompDataOffsetIPHigh = 12
seccompDataOffsetArgs = 16
)
func seccompDataOffsetArgLow(i int) uint32 {
return uint32(seccompDataOffsetArgs + i*8)
}
func seccompDataOffsetArgHigh(i int) uint32 {
return seccompDataOffsetArgLow(i) + 4
}
// MatchAny is marker to indicate any value will be accepted.
type MatchAny struct{}
func (a MatchAny) String() (s string) {
return "*"
}
// EqualTo specifies a value that needs to be strictly matched.
type EqualTo uintptr
func (a EqualTo) String() (s string) {
return fmt.Sprintf("== %#x", uintptr(a))
}
// NotEqual specifies a value that is strictly not equal.
type NotEqual uintptr
func (a NotEqual) String() (s string) {
return fmt.Sprintf("!= %#x", uintptr(a))
}
// GreaterThan specifies a value that needs to be strictly smaller.
type GreaterThan uintptr
func (a GreaterThan) String() (s string) {
return fmt.Sprintf("> %#x", uintptr(a))
}
// GreaterThanOrEqual specifies a value that needs to be smaller or equal.
type GreaterThanOrEqual uintptr
func (a GreaterThanOrEqual) String() (s string) {
return fmt.Sprintf(">= %#x", uintptr(a))
}
// LessThan specifies a value that needs to be strictly greater.
type LessThan uintptr
func (a LessThan) String() (s string) {
return fmt.Sprintf("< %#x", uintptr(a))
}
// LessThanOrEqual specifies a value that needs to be greater or equal.
type LessThanOrEqual uintptr
func (a LessThanOrEqual) String() (s string) {
return fmt.Sprintf("<= %#x", uintptr(a))
}
type maskedEqual struct {
mask uintptr
value uintptr
}
func (a maskedEqual) String() (s string) {
return fmt.Sprintf("& %#x == %#x", a.mask, a.value)
}
// MaskedEqual specifies a value that matches the input after the input is
// masked (bitwise &) against the given mask. Can be used to verify that input
// only includes certain approved flags.
func MaskedEqual(mask, value uintptr) any {
return maskedEqual{
mask: mask,
value: value,
}
}
// Rule stores the allowed syscall arguments.
//
// For example:
//
// rule := Rule {
// EqualTo(linux.ARCH_GET_FS | linux.ARCH_SET_FS), // arg0
// }
type Rule [7]any // 6 arguments + RIP
// RuleIP indicates what rules in the Rule array have to be applied to
// instruction pointer.
const RuleIP = 6
func (r Rule) String() (s string) {
if len(r) == 0 {
return
}
s += "( "
for _, arg := range r {
if arg != nil {
s += fmt.Sprintf("%v ", arg)
}
}
s += ")"
return
}
// SyscallRules stores a map of OR'ed argument rules indexed by the syscall number.
// If the 'Rules' is empty, we treat it as any argument is allowed.
//
// For example:
//
// rules := SyscallRules{
// syscall.SYS_FUTEX: []Rule{
// {
// MatchAny{},
// EqualTo(linux.FUTEX_WAIT | linux.FUTEX_PRIVATE_FLAG),
// }, // OR
// {
// MatchAny{},
// EqualTo(linux.FUTEX_WAKE | linux.FUTEX_PRIVATE_FLAG),
// },
// },
// syscall.SYS_GETPID: []Rule{},
//
// }
type SyscallRules map[uintptr][]Rule
// NewSyscallRules returns a new SyscallRules.
func NewSyscallRules() SyscallRules {
return make(map[uintptr][]Rule)
}
// AddRule adds the given rule. It will create a new entry for a new syscall, otherwise
// it will append to the existing rules.
func (sr SyscallRules) AddRule(sysno uintptr, r Rule) {
if cur, ok := sr[sysno]; ok {
// An empty rules means allow all. Honor it when more rules are added.
if len(cur) == 0 {
sr[sysno] = append(sr[sysno], Rule{})
}
sr[sysno] = append(sr[sysno], r)
} else {
sr[sysno] = []Rule{r}
}
}
// Merge merges the given SyscallRules.
func (sr SyscallRules) Merge(rules SyscallRules) {
for sysno, rs := range rules {
if cur, ok := sr[sysno]; ok {
// An empty rules means allow all. Honor it when more rules are added.
if len(cur) == 0 {
sr[sysno] = append(sr[sysno], Rule{})
}
if len(rs) == 0 {
rs = []Rule{{}}
}
sr[sysno] = append(sr[sysno], rs...)
} else {
sr[sysno] = rs
}
}
}
// DenyNewExecMappings is a set of rules that denies creating new executable
// mappings and converting existing ones.
var DenyNewExecMappings = SyscallRules{
unix.SYS_MMAP: []Rule{
{
MatchAny{},
MatchAny{},
MaskedEqual(unix.PROT_EXEC, unix.PROT_EXEC),
},
},
unix.SYS_MPROTECT: []Rule{
{
MatchAny{},
MatchAny{},
MaskedEqual(unix.PROT_EXEC, unix.PROT_EXEC),
},
},
}
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