parisc: Fix kernel panic due invalid values in IAOQ0 or IAOQ1

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>
Cc: <stable@vger.kernel.org>
Tested-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: Helge Deller <deller@gmx.de>

1 files changed, 18 insertions, 10 deletions

diff --git a/arch/parisc/kernel/ptrace.c b/arch/parisc/kernel/ptrace.c
index f642ba378ffa..040ff16dd5e7 100644
--- a/arch/parisc/kernel/ptrace.c
+++ b/arch/parisc/kernel/ptrace.c
@@ -167,6 +167,9 @@ long arch_ptrace(struct task_struct *child, long request,
                 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) ||
@@ -228,16 +231,18 @@ long arch_ptrace(struct task_struct *child, long request,
 
 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,
@@ -281,9 +286,12 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
                         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) ||