* [PATCH] powerpc: Check end of stack canary at oops time
@ 2010-08-24 23:15 Anton Blanchard
2010-08-25 1:29 ` Michael Ellerman
2010-08-30 0:18 ` Benjamin Herrenschmidt
0 siblings, 2 replies; 4+ messages in thread
From: Anton Blanchard @ 2010-08-24 23:15 UTC (permalink / raw)
To: benh; +Cc: linuxppc-dev
Add a check for the stack canary when we oops, similar to x86. This should make
it clear that we overran our stack:
Unable to handle kernel paging request for data at address 0x24652f63700ac689
Faulting instruction address: 0xc000000000063d24
Thread overran stack, or stack corrupted
Signed-off-by: Anton Blanchard <anton@samba.org>
---
Index: powerpc.git/arch/powerpc/mm/fault.c
===================================================================
--- powerpc.git.orig/arch/powerpc/mm/fault.c 2010-08-25 08:41:08.230086186 +1000
+++ powerpc.git/arch/powerpc/mm/fault.c 2010-08-25 09:12:38.276553103 +1000
@@ -30,6 +30,7 @@
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/perf_event.h>
+#include <linux/magic.h>
#include <asm/firmware.h>
#include <asm/page.h>
@@ -385,6 +386,7 @@ do_sigbus:
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
const struct exception_table_entry *entry;
+ unsigned long *stackend;
/* Are we prepared to handle this fault? */
if ((entry = search_exception_tables(regs->nip)) != NULL) {
@@ -413,5 +415,9 @@ void bad_page_fault(struct pt_regs *regs
printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
regs->nip);
+ stackend = end_of_stack(current);
+ if (current != &init_task && *stackend != STACK_END_MAGIC)
+ printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
+
die("Kernel access of bad area", regs, sig);
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] powerpc: Check end of stack canary at oops time
2010-08-24 23:15 [PATCH] powerpc: Check end of stack canary at oops time Anton Blanchard
@ 2010-08-25 1:29 ` Michael Ellerman
2010-08-25 1:51 ` Anton Blanchard
2010-08-30 0:18 ` Benjamin Herrenschmidt
1 sibling, 1 reply; 4+ messages in thread
From: Michael Ellerman @ 2010-08-25 1:29 UTC (permalink / raw)
To: Anton Blanchard; +Cc: linuxppc-dev
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On Wed, 2010-08-25 at 09:15 +1000, Anton Blanchard wrote:
> Add a check for the stack canary when we oops, similar to x86. This should make
> it clear that we overran our stack:
>
> Unable to handle kernel paging request for data at address 0x24652f63700ac689
> Faulting instruction address: 0xc000000000063d24
> Thread overran stack, or stack corrupted
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>
> Index: powerpc.git/arch/powerpc/mm/fault.c
> ===================================================================
> --- powerpc.git.orig/arch/powerpc/mm/fault.c 2010-08-25 08:41:08.230086186 +1000
> +++ powerpc.git/arch/powerpc/mm/fault.c 2010-08-25 09:12:38.276553103 +1000
> @@ -30,6 +30,7 @@
> #include <linux/kprobes.h>
> #include <linux/kdebug.h>
> #include <linux/perf_event.h>
> +#include <linux/magic.h>
>
> #include <asm/firmware.h>
> #include <asm/page.h>
> @@ -385,6 +386,7 @@ do_sigbus:
> void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
> {
> const struct exception_table_entry *entry;
> + unsigned long *stackend;
>
> /* Are we prepared to handle this fault? */
> if ((entry = search_exception_tables(regs->nip)) != NULL) {
> @@ -413,5 +415,9 @@ void bad_page_fault(struct pt_regs *regs
> printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
> regs->nip);
>
> + stackend = end_of_stack(current);
> + if (current != &init_task && *stackend != STACK_END_MAGIC)
> + printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
The check for init is just because we haven't set the magic value for
init's stack right? But we could.
cheers
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] powerpc: Check end of stack canary at oops time
2010-08-25 1:29 ` Michael Ellerman
@ 2010-08-25 1:51 ` Anton Blanchard
0 siblings, 0 replies; 4+ messages in thread
From: Anton Blanchard @ 2010-08-25 1:51 UTC (permalink / raw)
To: Michael Ellerman; +Cc: linuxppc-dev
Hi,
> The check for init is just because we haven't set the magic value for
> init's stack right? But we could.
Yeah, it's similar to what x86 are doing now:
commit 0e7810be30f66e9f430c4ce2cd3b14634211690f
Author: Jan Beulich <JBeulich@novell.com>
Date: Fri Nov 20 14:00:14 2009 +0000
x86: Suppress stack overrun message for init_task
init_task doesn't get its stack end location set to
STACK_END_MAGIC, and hence the message is confusing
rather than helpful in this case.
Adding it directly to init_task would be nice but I suspect we'd
either have to make assumptions about end_of_stack in our code or move the
canary into the thread_info (so we can statically allocate it via
INIT_THREAD_INFO()) or do it at runtime somewhere, hopefully early enough that
we couldn't take an oops.
Anton
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] powerpc: Check end of stack canary at oops time
2010-08-24 23:15 [PATCH] powerpc: Check end of stack canary at oops time Anton Blanchard
2010-08-25 1:29 ` Michael Ellerman
@ 2010-08-30 0:18 ` Benjamin Herrenschmidt
1 sibling, 0 replies; 4+ messages in thread
From: Benjamin Herrenschmidt @ 2010-08-30 0:18 UTC (permalink / raw)
To: Anton Blanchard; +Cc: linuxppc-dev
On Wed, 2010-08-25 at 09:15 +1000, Anton Blanchard wrote:
> /* Are we prepared to handle this fault? */
> if ((entry = search_exception_tables(regs->nip)) != NULL) {
> @@ -413,5 +415,9 @@ void bad_page_fault(struct pt_regs *regs
> printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
> regs->nip);
>
> + stackend = end_of_stack(current);
> + if (current != &init_task && *stackend != STACK_END_MAGIC)
> + printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
> +
> die("Kernel access of bad area", regs, sig);
> }
Is it worth making it a __get_user or similar just in case ? I suppose
if the stack is really busted we wouldn't even have reached that
code ...
Cheers,
Ben.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2010-08-24 23:15 [PATCH] powerpc: Check end of stack canary at oops time Anton Blanchard
2010-08-25 1:29 ` Michael Ellerman
2010-08-25 1:51 ` Anton Blanchard
2010-08-30 0:18 ` Benjamin Herrenschmidt
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