seccomp: Document two-phase seccomp and arch-provided seccomp_data
The description of how archs should implement seccomp filters was
still strictly correct, but it failed to describe the newly
available optimizations.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/arch/Kconfig b/arch/Kconfig
index 0eae9df..05d7a8a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -323,6 +323,17 @@
results in the system call being skipped immediately.
- seccomp syscall wired up
+ For best performance, an arch should use seccomp_phase1 and
+ seccomp_phase2 directly. It should call seccomp_phase1 for all
+ syscalls if TIF_SECCOMP is set, but seccomp_phase1 does not
+ need to be called from a ptrace-safe context. It must then
+ call seccomp_phase2 if seccomp_phase1 returns anything other
+ than SECCOMP_PHASE1_OK or SECCOMP_PHASE1_SKIP.
+
+ As an additional optimization, an arch may provide seccomp_data
+ directly to seccomp_phase1; this avoids multiple calls
+ to the syscall_xyz helpers for every syscall.
+
config SECCOMP_FILTER
def_bool y
depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
