Add support for OCI seccomp filters in the sandbox.

OCI configuration includes support for specifying seccomp filters. In runc,
these filter configurations are converted into seccomp BPF programs and loaded
into the kernel via libseccomp. runsc needs to be a static binary so, for
runsc, we cannot rely on a C library and need to implement the functionality
in Go.

The generator added here implements basic support for taking OCI seccomp
configuration and converting it into a seccomp BPF program with the same
behavior as a program generated by libseccomp.

- New conditional operations were added to pkg/seccomp to support operations
  available in OCI.
- AllowAny and AllowValue were renamed to MatchAny and EqualTo to better reflect
  that syscalls matching the conditionals result in the provided action not
  simply SCMP_RET_ALLOW.
- BuildProgram in pkg/seccomp no longer panics if provided an empty list of
  rules. It now builds a program with the architecture sanity check only.
- ProgramBuilder now allows adding labels that are unused. However, backwards
  jumps are still not permitted.

Fixes #510

PiperOrigin-RevId: 331938697

1 files changed, 10 insertions, 0 deletions

diff --git a/pkg/sentry/kernel/syscalls.go b/pkg/sentry/kernel/syscalls.go
index 413111faf..332bdb8e8 100644
--- a/pkg/sentry/kernel/syscalls.go
+++ b/pkg/sentry/kernel/syscalls.go
@@ -348,6 +348,16 @@ func (s *SyscallTable) LookupName(sysno uintptr) string {
 	return fmt.Sprintf("sys_%d", sysno) // Unlikely.
 }
 
+// LookupNo looks up a syscall number by name.
+func (s *SyscallTable) LookupNo(name string) (uintptr, error) {
+	for i, syscall := range s.Table {
+		if syscall.Name == name {
+			return uintptr(i), nil
+		}
+	}
+	return 0, fmt.Errorf("syscall %q not found", name)
+}
+
 // LookupEmulate looks up an emulation syscall number.
 func (s *SyscallTable) LookupEmulate(addr usermem.Addr) (uintptr, bool) {
 	sysno, ok := s.Emulate[addr]