linux-kernel - [PATCH v3 4/8] seccomp: Document two-phase seccomp and arch-provided seccomp

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Date:	Mon, 21 Jul 2014 18:49:17 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	Will Drewry <wad@...omium.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
	linux-arch@...r.kernel.org, linux-security-module@...r.kernel.org,
	Alexei Starovoitov <ast@...mgrid.com>, hpa@...or.com,
	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH v3 4/8] 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@...capital.net>
---
 arch/Kconfig | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/Kconfig b/arch/Kconfig
index 0eae9df..05d7a8a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -323,6 +323,17 @@ config HAVE_ARCH_SECCOMP_FILTER
 	    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
-- 
1.9.3

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