[PATCH v3 08/14] parisc: mask compat syscall arguments in syscall_get_arguments()

[Ricardo Robaina]

A 32-bit compat task may leave garbage in the upper 32 bits of the
argument registers. Mask it off in syscall_get_arguments() so that
in-kernel consumers such as seccomp and audit observe the same values
the syscall actually used.

This previously happened for audit in the parisc do_syscall_trace_enter()
compat path; do it in the helper so all callers benefit and to prepare
for passing pt_regs to audit_syscall_entry().

Signed-off-by: Ricardo Robaina <rrobaina at redhat.com>
---
 arch/parisc/include/asm/syscall.h | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/parisc/include/asm/syscall.h b/arch/parisc/include/asm/syscall.h
index c11222798ab2..9d10fada3b48 100644
--- a/arch/parisc/include/asm/syscall.h
+++ b/arch/parisc/include/asm/syscall.h
@@ -28,12 +28,18 @@ static inline void syscall_get_arguments(struct task_struct *tsk,
 					 struct pt_regs *regs,
 					 unsigned long *args)
 {
-	args[5] = regs->gr[21];
-	args[4] = regs->gr[22];
-	args[3] = regs->gr[23];
-	args[2] = regs->gr[24];
-	args[1] = regs->gr[25];
-	args[0] = regs->gr[26];
+	unsigned long mask = -1UL;
+
+	/* Mask off garbage in the upper 32 bits for compat tasks. */
+	if (__is_compat_task(tsk))
+		mask = 0xffffffff;
+
+	args[5] = regs->gr[21] & mask;
+	args[4] = regs->gr[22] & mask;
+	args[3] = regs->gr[23] & mask;
+	args[2] = regs->gr[24] & mask;
+	args[1] = regs->gr[25] & mask;
+	args[0] = regs->gr[26] & mask;
 }
 
 static inline void syscall_set_arguments(struct task_struct *tsk,
-- 
2.55.0