[patch 015/104] parisc: fix kernel crash when unwinding a userspace process

Greg KH
2008-12-03T19:56:22Z

[-- Attachment #1: parisc-fix-kernel-crash-when-unwinding-a-userspace-process.patch --]
[-- Type: text/plain, Size: 4154 bytes --]

2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------
From: Helge Deller <deller@gmx.de>

commit 7a3f5134a8f5bd7fa38b5645eef05e8a4eb62951 upstream.

Any user on existing parisc 32- and 64bit-kernels can easily crash
the kernel and as such enforce a DSO.
A simple testcase is available here:
http://gsyprf10.external.hp.com/~deller/crash.tgz

The problem is introduced by the fact, that the handle_interruption()
crash handler calls the show_regs() function, which in turn tries to
unwind the stack by calling parisc_show_stack(). Since the stack contains
userspace addresses, a try to unwind the stack is dangerous and useless
and leads to the crash.

The fix is trivial: For userspace processes
a) avoid to unwind the stack, and
b) avoid to resolve userspace addresses to kernel symbol names.

While touching this code, I converted print_symbol() to %pS
printk formats and made parisc_show_stack() static.

An initial patch for this was written by Kyle McMartin back in August:
http://marc.info/?l=linux-parisc&m=121805168830283&w=2

Compile and run-tested with a 64bit parisc kernel.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: Grant Grundler <grundler@parisc-linux.org>
Cc: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/parisc/kernel/traps.c | 41 ++++++++++++++++++++---------------------
1 file changed, 20 insertions(+), 21 deletions(-)

--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -24,7 +24,6 @@
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/console.h>
-#include <linux/kallsyms.h>
#include <linux/bug.h>

#include <asm/assembly.h>
@@ -51,7 +50,7 @@
DEFINE_SPINLOCK(pa_dbit_lock);
#endif

-void parisc_show_stack(struct task_struct *t, unsigned long *sp,
+static void parisc_show_stack(struct task_struct *task, unsigned long *sp,
struct pt_regs *regs);

static int printbinary(char *buf, unsigned long x, int nbits)
@@ -121,18 +120,19 @@ static void print_fr(char *level, struct

void show_regs(struct pt_regs *regs)
{
- int i;
+ int i, user;
char *level;
unsigned long cr30, cr31;

- level = user_mode(regs) ? KERN_DEBUG : KERN_CRIT;
+ user = user_mode(regs);
+ level = user ? KERN_DEBUG : KERN_CRIT;

print_gr(level, regs);

for (i = 0; i < 8; i += 4)
PRINTREGS(level, regs->sr, "sr", RFMT, i);

- if (user_mode(regs))
+ if (user)
print_fr(level, regs);

cr30 = mfctl(30);
@@ -145,14 +145,18 @@ void show_regs(struct pt_regs *regs)
printk("%s CPU: %8d CR30: " RFMT " CR31: " RFMT "\n",
level, current_thread_info()->cpu, cr30, cr31);
printk("%s ORIG_R28: " RFMT "\n", level, regs->orig_r28);
- printk(level);
- print_symbol(" IAOQ[0]: %s\n", regs->iaoq[0]);
- printk(level);
- print_symbol(" IAOQ[1]: %s\n", regs->iaoq[1]);
- printk(level);
- print_symbol(" RP(r2): %s\n", regs->gr[2]);

- parisc_show_stack(current, NULL, regs);
+ if (user) {
+ printk("%s IAOQ[0]: " RFMT "\n", level, regs->iaoq[0]);
+ printk("%s IAOQ[1]: " RFMT "\n", level, regs->iaoq[1]);
+ printk("%s RP(r2): " RFMT "\n", level, regs->gr[2]);
+ } else {
+ printk("%s IAOQ[0]: %pS\n", level, (void *) regs->iaoq[0]);
+ printk("%s IAOQ[1]: %pS\n", level, (void *) regs->iaoq[1]);
+ printk("%s RP(r2): %pS\n", level, (void *) regs->gr[2]);
+
+ parisc_show_stack(current, NULL, regs);
+ }
}

@@ -173,20 +177,15 @@ static void do_show_stack(struct unwind_
break;

if (__kernel_text_address(info->ip)) {
- printk("%s [<" RFMT ">] ", (i&0x3)==1 ? KERN_CRIT : "", info->ip);
-#ifdef CONFIG_KALLSYMS
- print_symbol("%s\n", info->ip);
-#else
- if ((i & 0x03) == 0)
- printk("\n");
-#endif
+ printk(KERN_CRIT " [<" RFMT ">] %pS\n",
+ info->ip, (void *) info->ip);
i++;
}
}
- printk("\n");
+ printk(KERN_CRIT "\n");
}

-void parisc_show_stack(struct task_struct *task, unsigned long *sp,
+static void parisc_show_stack(struct task_struct *task, unsigned long *sp,
struct pt_regs *regs)
{
struct unwind_frame_info info;