seccomp: Allow arch code to provide seccomp_data

populate_seccomp_data is expensive: it works by inspecting
task_pt_regs and various other bits to piece together all the
information, and it's does so in multiple partially redundant steps.

Arch-specific code in the syscall entry path can do much better.

Admittedly this adds a bit of additional room for error, but the
speedup should be worth it.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Kees Cook <keescook@chromium.org>

include/linux/seccomp.h

@@ -39,7 +39,7 @@ static inline int secure_computing(void)
 #define SECCOMP_PHASE1_OK	0
 #define SECCOMP_PHASE1_SKIP	1
 
-extern u32 seccomp_phase1(void);
+extern u32 seccomp_phase1(struct seccomp_data *sd);
 int seccomp_phase2(u32 phase1_result);
 #else
 extern void secure_computing_strict(int this_syscall);