[PATCH] powerpc: Check end of stack canary at oops time

STALE5830d

4 messages, 3 authors, 2010-08-30 · open the first message on its own page

[PATCH] powerpc: Check end of stack canary at oops time

From: Anton Blanchard <hidden>
Date: 2010-08-24 23:15:28 

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 <redacted>
---

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);
 }

Re: [PATCH] powerpc: Check end of stack canary at oops time

From: Michael Ellerman <hidden>
Date: 2010-08-25 01:29:38 

On Wed, 2010-08-25 at 09:15 +1000, Anton Blanchard wrote:
quoted hunk
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 <redacted>
---

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

Re: [PATCH] powerpc: Check end of stack canary at oops time

From: Anton Blanchard <hidden>
Date: 2010-08-25 01:51:12 

 
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 [off-list ref]
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

Re: [PATCH] powerpc: Check end of stack canary at oops time

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: 2010-08-30 00:18:28 

On Wed, 2010-08-25 at 09:15 +1000, Anton Blanchard wrote:
quoted hunk
 	/* 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.
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