MIPS: seccomp: Support compat with both O32 and N32

Previously the seccomp would only support strict mode on O32 userland
programs when the kernel had support for both O32 and N32 ABIs. Remove
kludge and support both ABIs.

With this patch in place, the seccomp_bpf self test now passes
global.mode_strict_support with N32 userland.

Suggested-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: IMG-MIPSLinuxKerneldevelopers@imgtec.com
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12917/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/seccomp.h

@@ -2,27 +2,32 @@
 
 #include <linux/unistd.h>
 
-/*
- * Kludge alert:
- *
- * The generic seccomp code currently allows only a single compat ABI.	Until
- * this is fixed we priorize O32 as the compat ABI over N32.
- */
-#ifdef CONFIG_MIPS32_O32
-
-#define __NR_seccomp_read_32		4003
-#define __NR_seccomp_write_32		4004
-#define __NR_seccomp_exit_32		4001
-#define __NR_seccomp_sigreturn_32	4193	/* rt_sigreturn */
-
-#elif defined(CONFIG_MIPS32_N32)
-
-#define __NR_seccomp_read_32		6000
-#define __NR_seccomp_write_32		6001
-#define __NR_seccomp_exit_32		6058
-#define __NR_seccomp_sigreturn_32	6211	/* rt_sigreturn */
-
-#endif /* CONFIG_MIPS32_O32 */
+#ifdef CONFIG_COMPAT
+static inline const int *get_compat_mode1_syscalls(void)
+{
+	static const int syscalls_O32[] = {
+		__NR_O32_Linux + 3, __NR_O32_Linux + 4,
+		__NR_O32_Linux + 1, __NR_O32_Linux + 193,
+		0, /* null terminated */
+	};
+	static const int syscalls_N32[] = {
+		__NR_N32_Linux + 0, __NR_N32_Linux + 1,
+		__NR_N32_Linux + 58, __NR_N32_Linux + 211,
+		0, /* null terminated */
+	};
+
+	if (config_enabled(CONFIG_MIPS32_O32) && test_thread_flag(TIF_32BIT_REGS))
+		return syscalls_O32;
+
+	if (config_enabled(CONFIG_MIPS32_N32))
+		return syscalls_N32;
+
+	BUG();
+}
+
+#define get_compat_mode1_syscalls get_compat_mode1_syscalls
+
+#endif /* CONFIG_COMPAT */
 
 #include <asm-generic/seccomp.h>