MIPS: seccomp: Handle indirect system calls (o32)

When userland uses syscall() to perform an indirect system call
the actually system call that needs to be checked by the filter
is on the first argument. The kernel code needs to handle this case
by looking at the original syscall number in v0 and if it's
NR_syscall, then it needs to examine the first argument to
identify the real system call that will be executed.
Similarly, we need to 'virtually' shift the syscall() arguments
so the syscall_get_arguments() function can fetch the correct
arguments for the indirect system call.

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6404/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 19 insertions, 1 deletions

diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
index 08b639b1ca78..9031745cec1b 100644
--- a/arch/mips/include/asm/syscall.h
+++ b/arch/mips/include/asm/syscall.h
@@ -19,11 +19,22 @@
 #include <linux/sched.h>
 #include <linux/uaccess.h>
 #include <asm/ptrace.h>
+#include <asm/unistd.h>
+
+#ifndef __NR_syscall /* Only defined if _MIPS_SIM == _MIPS_SIM_ABI32 */
+#define __NR_syscall 4000
+#endif
 
 static inline long syscall_get_nr(struct task_struct *task,
 				  struct pt_regs *regs)
 {
-	return regs->regs[2];
+	/* O32 ABI syscall() - Either 64-bit with O32 or 32-bit */
+	if ((config_enabled(CONFIG_32BIT) ||
+	    test_tsk_thread_flag(task, TIF_32BIT_REGS)) &&
+	    (regs->regs[2] == __NR_syscall))
+		return regs->regs[4];
+	else
+		return regs->regs[2];
 }
 
 static inline unsigned long mips_get_syscall_arg(unsigned long *arg,
@@ -91,6 +102,13 @@ static inline void syscall_get_arguments(struct task_struct *task,
 {
 	unsigned long arg;
 	int ret;
+	/* O32 ABI syscall() - Either 64-bit with O32 or 32-bit */
+	if ((config_enabled(CONFIG_32BIT) ||
+	    test_tsk_thread_flag(task, TIF_32BIT_REGS)) &&
+	    (regs->regs[2] == __NR_syscall)) {
+		i++;
+		n++;
+	}
 
 	while (n--)
 		ret |= mips_get_syscall_arg(&arg, task, regs, i++);