From: Anton Blanchard <anton@samba•org>
To: David Wilder <dwilder@us•ibm.com>
Cc: Linuxppc-dev@ozlabs•org
Subject: Re: Unable to handle kernel paging request in show_instructions
Date: Tue, 20 Jun 2006 23:47:43 +1000 [thread overview]
Message-ID: <20060620134742.GA2518@krispykreme> (raw)
In-Reply-To: <4497445F.50700@us.ibm.com>
Hi David,
> The problem occures in show_instructions(). Show_instructions() takes
> the NIP (D00000000002201) and subtracts some number so it points several
> instructs before the failing instructions. In this case the new value
> is on a previous page and that page is not valid (it is not mapped).
> When the new NIP is referenced we get a second fault.
>
> show_instructions tries to validate addresses by checking if it is the
> kernel segment (0xc.....) or the first vmalloc segment (0xD.......).
> But in this case the validation passes even though the address is
> invalid. Any ideas how to fix this? Is there a easy way to validate
> if a page is valid before accessing it?
Whats interesting is that bad_page_fault should have walked the
exception tables and recovered, considering we have a __get_user call in
show_instructions.
While we should really understand why this failed, I suspect we should
be tighter with our checking. It looks like __kernel_text_address()
does what we want. Untested patch below.
Anton
Use __kernel_text_address when validating instruction addresses in the
Oops code.
Signed-off-by: Anton Blanchard <anton@samba•org>
---
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -342,13 +342,6 @@ #endif
static int instructions_to_print = 16;
-#ifdef CONFIG_PPC64
-#define BAD_PC(pc) ((REGION_ID(pc) != KERNEL_REGION_ID) && \
- (REGION_ID(pc) != VMALLOC_REGION_ID))
-#else
-#define BAD_PC(pc) ((pc) < KERNELBASE)
-#endif
-
static void show_instructions(struct pt_regs *regs)
{
int i;
@@ -367,7 +360,8 @@ static void show_instructions(struct pt_
* bad address because the pc *should* only be a
* kernel address.
*/
- if (BAD_PC(pc) || __get_user(instr, (unsigned int __user *)pc)) {
+ if (!__kernel_text_address(pc) ||
+ __get_user(instr, (unsigned int __user *)pc)) {
printk("XXXXXXXX ");
} else {
if (regs->nip == pc)
prev parent reply other threads:[~2006-06-20 13:47 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-06-20 0:42 Unable to handle kernel paging request in show_instructions David Wilder
2006-06-20 0:44 ` Arnd Bergmann
2006-06-20 13:47 ` Anton Blanchard [this message]
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