seccomp: add support for "swapcontext" syscall in default policy

This system call is only available on the 32- and 64-bit PowerPC, it is
used by modern programming language implementations (such as gcc-go) to
implement coroutine features through userspace context switches.

Other container environment, such as Systemd nspawn already whitelist
this system call in their seccomp profile [1] [2]. As such, it would be
nice to also whitelist it in moby.

This issue was encountered on Alpine Linux GitLab CI system, which uses
moby, when attempting to execute gcc-go compiled software on ppc64le.

[1]: https://github.com/systemd/systemd/pull/9487
[2]: https://github.com/systemd/systemd/issues/9485

Signed-off-by: Sören Tempel <soeren+git@soeren-tempel.net>

profiles/seccomp/default.json

@@ -474,7 +474,8 @@
 		},
 		{
 			"names": [
-				"sync_file_range2"
+				"sync_file_range2",
+				"swapcontext"
 			],
 			"action": "SCMP_ACT_ALLOW",
 			"includes": {

profiles/seccomp/default_linux.go

@@ -474,6 +474,7 @@ func DefaultProfile() *Seccomp {
 			LinuxSyscall: specs.LinuxSyscall{
 				Names: []string{
 					"sync_file_range2",
+					"swapcontext",
 				},
 				Action: specs.ActAllow,
 			},