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

2 files changed, 5 insertions, 0 deletions

diff --git a/runsc/config/config.go b/runsc/config/config.go
index df134bb2f..f30f79f68 100644
--- a/runsc/config/config.go
+++ b/runsc/config/config.go
@@ -157,8 +157,12 @@ type Config struct {
 	// Enables FUSE usage.
 	FUSE bool `flag:"fuse"`
 
+	// Allows overriding of flags in OCI annotations.
 	AllowFlagOverride bool `flag:"allow-flag-override"`
 
+	// Enables seccomp inside the sandbox.
+	OCISeccomp bool `flag:"oci-seccomp"`
+
 	// TestOnlyAllowRunAsCurrentUserWithoutChroot should only be used in
 	// tests. It allows runsc to start the sandbox process as the current
 	// user, and without chrooting the sandbox process. This can be
diff --git a/runsc/config/flags.go b/runsc/config/flags.go
index eff46e938..a5f25cfa2 100644
--- a/runsc/config/flags.go
+++ b/runsc/config/flags.go
@@ -63,6 +63,7 @@ func RegisterFlags() {
 		flag.Bool("rootless", false, "it allows the sandbox to be started with a user that is not root. Sandbox and Gofer processes may run with same privileges as current user.")
 		flag.Var(leakModePtr(refs.NoLeakChecking), "ref-leak-mode", "sets reference leak check mode: disabled (default), log-names, log-traces.")
 		flag.Bool("cpu-num-from-quota", false, "set cpu number to cpu quota (least integer greater or equal to quota value, but not less than 2)")
+		flag.Bool("oci-seccomp", false, "Enables loading OCI seccomp filters inside the sandbox.")
 
 		// Flags that control sandbox runtime behavior: FS related.
 		flag.Var(fileAccessTypePtr(FileAccessExclusive), "file-access", "specifies which filesystem to use for the root mount: exclusive (default), shared. Volume mounts are always shared.")