arch/x86: add syscall_get_arch to syscall.h

Add syscall_get_arch() to export the current AUDIT_ARCH_* based on system call
entry path.

Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Reviewed-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: Eric Paris <eparis@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>

v18: - update comment about x32 tasks
     - rebase to v3.4-rc2
v17: rebase and reviewed-by
v14: rebase/nochanges
v13: rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc
Signed-off-by: James Morris <james.l.morris@oracle.com>

arch/x86/include/asm/syscall.h

@@ -13,9 +13,11 @@
 #ifndef _ASM_X86_SYSCALL_H
 #define _ASM_X86_SYSCALL_H
 
+#include <linux/audit.h>
 #include <linux/sched.h>
 #include <linux/err.h>
 #include <asm/asm-offsets.h>	/* For NR_syscalls */
+#include <asm/thread_info.h>	/* for TS_COMPAT */
 #include <asm/unistd.h>
 
 extern const unsigned long sys_call_table[];
@@ -88,6 +90,12 @@ static inline void syscall_set_arguments(struct task_struct *task,
 	memcpy(&regs->bx + i, args, n * sizeof(args[0]));
 }
 
+static inline int syscall_get_arch(struct task_struct *task,
+				   struct pt_regs *regs)
+{
+	return AUDIT_ARCH_I386;
+}
+
 #else	 /* CONFIG_X86_64 */
 
 static inline void syscall_get_arguments(struct task_struct *task,
@@ -212,6 +220,25 @@ static inline void syscall_set_arguments(struct task_struct *task,
 		}
 }
 
+static inline int syscall_get_arch(struct task_struct *task,
+				   struct pt_regs *regs)
+{
+#ifdef CONFIG_IA32_EMULATION
+	/*
+	 * TS_COMPAT is set for 32-bit syscall entry and then
+	 * remains set until we return to user mode.
+	 *
+	 * TIF_IA32 tasks should always have TS_COMPAT set at
+	 * system call time.
+	 *
+	 * x32 tasks should be considered AUDIT_ARCH_X86_64.
+	 */
+	if (task_thread_info(task)->status & TS_COMPAT)
+		return AUDIT_ARCH_I386;
+#endif
+	/* Both x32 and x86_64 are considered "64-bit". */
+	return AUDIT_ARCH_X86_64;
+}
 #endif	/* CONFIG_X86_32 */
 
 #endif	/* _ASM_X86_SYSCALL_H */