MIPS: compat: Don't clobber personality bits in 32-bit sys_personality().

If PER_LINUX32 has been set on a 32-bit kernel, only twiddle with the
low-order personality bits, let the upper bits pass through.
Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Cc: Camm Maguire <camm@maguirefamily.org>
Patchwork: https://patchwork.linux-mips.org/patch/1751/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/linux32.c

@@ -251,14 +251,15 @@ SYSCALL_DEFINE5(n32_msgrcv, int, msqid, u32, msgp, size_t, msgsz,
 
 SYSCALL_DEFINE1(32_personality, unsigned long, personality)
 {
+	unsigned int p = personality & 0xffffffff;
 	int ret;
-	personality &= 0xffffffff;
+
 	if (personality(current->personality) == PER_LINUX32 &&
-	    personality == PER_LINUX)
-		personality = PER_LINUX32;
-	ret = sys_personality(personality);
-	if (ret == PER_LINUX32)
-		ret = PER_LINUX;
+	    personality(p) == PER_LINUX)
+		p = (p & ~PER_MASK) | PER_LINUX32;
+	ret = sys_personality(p);
+	if (ret != -1 && personality(ret) == PER_LINUX32)
+		ret = (ret & ~PER_MASK) | PER_LINUX;
 	return ret;
 }