[PATCH 3.16 44/47] parisc: Fix kernel panic due invalid values in IAOQ0 or IAOQ1

[Ben Hutchings <ben@decadent.org.uk>]

3.16.76-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Helge Deller <deller@gmx.de>

commit 10835c854685393a921b68f529bf740fa7c9984d upstream.

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 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 calls in the native and compat ptrace paths.

Link: https://bugs.gentoo.org/481768
Reported-by: Jeroen Roovers <jer@gentoo.org>
Tested-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 arch/parisc/kernel/ptrace.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

--- a/arch/parisc/kernel/ptrace.c
+++ b/arch/parisc/kernel/ptrace.c
@@ -155,6 +155,9 @@ long arch_ptrace(struct task_struct *chi
 		if ((addr & (sizeof(unsigned long)-1)) ||
 		     addr >= sizeof(struct pt_regs))
 			break;
+		if (addr == PT_IAOQ0 || addr == PT_IAOQ1) {
+			data |= 3; /* ensure userspace privilege */
+		}
 		if ((addr >= PT_GR1 && addr <= PT_GR31) ||
 				addr == PT_IAOQ0 || addr == PT_IAOQ1 ||
 				(addr >= PT_FR0 && addr <= PT_FR31 + 4) ||
@@ -188,16 +191,18 @@ long arch_ptrace(struct task_struct *chi
 
 static compat_ulong_t translate_usr_offset(compat_ulong_t offset)
 {
-	if (offset < 0)
-		return sizeof(struct pt_regs);
-	else if (offset <= 32*4)	/* gr[0..31] */
-		return offset * 2 + 4;
-	else if (offset <= 32*4+32*8)	/* gr[0..31] + fr[0..31] */
-		return offset + 32*4;
-	else if (offset < sizeof(struct pt_regs)/2 + 32*4)
-		return offset * 2 + 4 - 32*8;
+	compat_ulong_t pos;
+
+	if (offset < 32*4)	/* gr[0..31] */
+		pos = offset * 2 + 4;
+	else if (offset < 32*4+32*8)	/* fr[0] ... fr[31] */
+		pos = (offset - 32*4) + PT_FR0;
+	else if (offset < sizeof(struct pt_regs)/2 + 32*4) /* sr[0] ... ipsw */
+		pos = (offset - 32*4 - 32*8) * 2 + PT_SR0 + 4;
 	else
-		return sizeof(struct pt_regs);
+		pos = sizeof(struct pt_regs);
+
+	return pos;
 }
 
 long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
@@ -241,9 +246,12 @@ long compat_arch_ptrace(struct task_stru
 			addr = translate_usr_offset(addr);
 			if (addr >= sizeof(struct pt_regs))
 				break;
+			if (addr == PT_IAOQ0+4 || addr == PT_IAOQ1+4) {
+				data |= 3; /* ensure userspace privilege */
+			}
 			if (addr >= PT_FR0 && addr <= PT_FR31 + 4) {
 				/* Special case, fp regs are 64 bits anyway */
-				*(__u64 *) ((char *) task_regs(child) + addr) = data;
+				*(__u32 *) ((char *) task_regs(child) + addr) = data;
 				ret = 0;
 			}
 			else if ((addr >= PT_GR1+4 && addr <= PT_GR31+4) ||