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Re: Breakage in arch/mips/kernel/traps.c for 64bit

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: Breakage in arch/mips/kernel/traps.c for 64bit
From: tsbogend@alpha.franken.de (Thomas Bogendoerfer)
Date: Sun, 4 May 2008 00:48:49 +0200
Cc: ralf@linux-mips.org, linux-mips@linux-mips.org
In-reply-to: <20080504.011647.93019265.anemo@mba.ocn.ne.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20080501163314.GA9955@alpha.franken.de> <20080502101113.GA24408@linux-mips.org> <20080504.011647.93019265.anemo@mba.ocn.ne.jp>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.13 (2006-08-11)
On Sun, May 04, 2008 at 01:16:47AM +0900, Atsushi Nemoto wrote:
> On Fri, 2 May 2008 11:11:13 +0100, Ralf Baechle <ralf@linux-mips.org> wrote:
> > It came as part of 39b8d5254246ac56342b72f812255c8f7a74dca9 which is a
> > patch amalgated from several other patches.  Below is the original patch
> > it came with.  I think the idea of the patch is valid but the idea needs a
> > bit of mending.
> 
> Then how about this fix?

hmm, why not simply use __get_user() when accessing the stack content ?
show_stacktrace() already does it for stack dumping ? This would
avoid any work for whatever sick stack mappings. Below is a patch,
which does this.

Thomas.

The newly added check for valid stack pointer address breaks at least for
64bit kernels.  Use __get_user() for accessing stack content to avoid crashes,
when doing the backtrace.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---

 arch/mips/kernel/traps.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c
index cb8b0e2..c9ce8d6 100644
--- a/arch/mips/kernel/traps.c
+++ b/arch/mips/kernel/traps.c
@@ -81,22 +81,22 @@ void (*board_bind_eic_interrupt)(int irq, int regset);
 
 static void show_raw_backtrace(unsigned long reg29)
 {
-       unsigned long *sp = (unsigned long *)(reg29 & ~3);
+       unsigned long __user *sp = (unsigned long __user *)(reg29 & ~3);
        unsigned long addr;
 
        printk("Call Trace:");
 #ifdef CONFIG_KALLSYMS
        printk("\n");
 #endif
-#define IS_KVA01(a) ((((unsigned int)a) & 0xc0000000) == 0x80000000)
-       if (IS_KVA01(sp)) {
-               while (!kstack_end(sp)) {
-                       addr = *sp++;
-                       if (__kernel_text_address(addr))
-                               print_ip_sym(addr);
+       while (!kstack_end(sp)) {
+               if (__get_user(addr, sp++)) {
+                       printk(" (Bad stack address)");
+                       break;
                }
-               printk("\n");
+               if (__kernel_text_address(addr))
+                       print_ip_sym(addr);
        }
+       printk("\n");
 }
 
 #ifdef CONFIG_KALLSYMS

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessary a
good idea.                                                [ RFC1925, 2.3 ]

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