parisc: Ensure userspace privilege for ptraced processes in regset functions

On parisc the privilege level of a process is stored in the lowest two bits of
the instruction pointers (IAOQ0 and IAOQ1). On Linux we use privilege level 0
for the kernel and privilege level 3 for user-space. So userspace should not be
allowed to modify IAOQ0 or IAOQ1 of a ptraced process to change it's privilege
level to e.g. 0 to try to gain kernel privileges.

This patch prevents such modifications in the regset support functions by
always setting the two lowest bits to one (which relates to privilege level 3
for user-space) if IAOQ0 or IAOQ1 are modified via ptrace regset calls.

Link: https://bugs.gentoo.org/481768
Cc: <stable@vger.kernel.org> # v4.7+
Tested-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/kernel/ptrace.c b/arch/parisc/kernel/ptrace.c
index 040ff16dd5e75cd6f9c097f077a18724def0acef..9f6ff7bc06f9a4d434888d0b800074dede80774a 100644 (file)
--- a/arch/parisc/kernel/ptrace.c
+++ b/arch/parisc/kernel/ptrace.c
@@ -504,7 +504,8 @@ static void set_reg(struct pt_regs *regs, int num, unsigned long val)
                        return;
        case RI(iaoq[0]):
        case RI(iaoq[1]):
-                       regs->iaoq[num - RI(iaoq[0])] = val;
+                       /* set 2 lowest bits to ensure userspace privilege: */
+                       regs->iaoq[num - RI(iaoq[0])] = val | 3;
                        return;
        case RI(sar):   regs->sar = val;
                        return;