MIPS: Add new AUDIT_ARCH token for the N32 ABI on MIPS64

A MIPS64 kernel may support ELF files for all 3 MIPS ABIs
(O32, N32, N64). Furthermore, the AUDIT_ARCH_MIPS{,EL}64 token
does not provide enough information about the ABI for the 64-bit
process. As a result of which, userland needs to use complex
seccomp filters to decide whether a syscall belongs to the o32 or n32
or n64 ABI. Therefore, a new arch token for MIPS64/n32 is added so it
can be used by seccomp to explicitely set syscall filters for this ABI.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Acked-by: Eric Paris <eparis@redhat.com>
Acked-by: Paul Moore <pmoore@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: linux-mips@linux-mips.org
Link: http://sourceforge.net/p/libseccomp/mailman/message/32239040/
Patchwork: https://patchwork.linux-mips.org/patch/6818/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/syscall.h

@@ -133,6 +133,8 @@ static inline int syscall_get_arch(void)
 #ifdef CONFIG_64BIT
 	if (!test_thread_flag(TIF_32BIT_REGS))
 		arch |= __AUDIT_ARCH_64BIT;
+	if (test_thread_flag(TIF_32BIT_ADDR))
+		arch |= __AUDIT_ARCH_CONVENTION_MIPS64_N32;
 #endif
 #if defined(__LITTLE_ENDIAN)
 	arch |=  __AUDIT_ARCH_LE;

include/uapi/linux/audit.h

@@ -331,9 +331,17 @@ enum {
 #define AUDIT_FAIL_PRINTK	1
 #define AUDIT_FAIL_PANIC	2
 
+/*
+ * These bits disambiguate different calling conventions that share an
+ * ELF machine type, bitness, and endianness
+ */
+#define __AUDIT_ARCH_CONVENTION_MASK 0x30000000
+#define __AUDIT_ARCH_CONVENTION_MIPS64_N32 0x20000000
+
 /* distinguish syscall tables */
 #define __AUDIT_ARCH_64BIT 0x80000000
 #define __AUDIT_ARCH_LE	   0x40000000
+
 #define AUDIT_ARCH_ALPHA	(EM_ALPHA|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
 #define AUDIT_ARCH_ARM		(EM_ARM|__AUDIT_ARCH_LE)
 #define AUDIT_ARCH_ARMEB	(EM_ARM)
@@ -346,7 +354,11 @@ enum {
 #define AUDIT_ARCH_MIPS		(EM_MIPS)
 #define AUDIT_ARCH_MIPSEL	(EM_MIPS|__AUDIT_ARCH_LE)
 #define AUDIT_ARCH_MIPS64	(EM_MIPS|__AUDIT_ARCH_64BIT)
+#define AUDIT_ARCH_MIPS64N32	(EM_MIPS|__AUDIT_ARCH_64BIT|\
+				 __AUDIT_ARCH_CONVENTION_MIPS64_N32)
 #define AUDIT_ARCH_MIPSEL64	(EM_MIPS|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE)
+#define AUDIT_ARCH_MIPSEL64N32	(EM_MIPS|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_LE\
+				 __AUDIT_ARCH_CONVENTION_MIPS64_N32)
 #define AUDIT_ARCH_OPENRISC	(EM_OPENRISC)
 #define AUDIT_ARCH_PARISC	(EM_PARISC)
 #define AUDIT_ARCH_PARISC64	(EM_PARISC|__AUDIT_ARCH_64BIT)