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authorEric Sandeen <sandeen@sandeen.net>2008-04-22 16:38:23 -0500
committerThomas Gleixner <tglx@linutronix.de>2008-05-26 16:15:33 +0200
commit7c9f8861e6c9c839f913e49b98c3854daca18f27 (patch)
tree220b23dff1aa11a83546fbc73a319575ca489188 /arch/x86
parentb40a4392a3c262e0d1b5379b4e142a8eefa63439 (diff)
stackprotector: use canary at end of stack to indicate overruns at oops time
(Updated with a common max-stack-used checker that knows about the canary, as suggested by Joe Perches) Use a canary at the end of the stack to clearly indicate at oops time whether the stack has ever overflowed. This is a very simple implementation with a couple of drawbacks: 1) a thread may legitimately use exactly up to the last word on the stack -- but the chances of doing this and then oopsing later seem slim 2) it's possible that the stack usage isn't dense enough that the canary location could get skipped over -- but the worst that happens is that we don't flag the overrun -- though this happens fairly often in my testing :( With the code in place, an intentionally-bloated stack oops might do: BUG: unable to handle kernel paging request at ffff8103f84cc680 IP: [<ffffffff810253df>] update_curr+0x9a/0xa8 PGD 8063 PUD 0 Thread overran stack or stack corrupted Oops: 0000 [1] SMP CPU 0 ... ... unless the stack overrun is so bad that it corrupts some other thread. Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86')
-rw-r--r--arch/x86/mm/fault.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index fd7e1798c75a..1f524df68b96 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -25,6 +25,7 @@
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/kdebug.h>
+#include <linux/magic.h>
#include <asm/system.h>
#include <asm/desc.h>
@@ -581,6 +582,8 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
unsigned long address;
int write, si_code;
int fault;
+ unsigned long *stackend;
+
#ifdef CONFIG_X86_64
unsigned long flags;
#endif
@@ -850,6 +853,10 @@ no_context:
show_fault_oops(regs, error_code, address);
+ stackend = end_of_stack(tsk);
+ if (*stackend != STACK_END_MAGIC)
+ printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
+
tsk->thread.cr2 = address;
tsk->thread.trap_no = 14;
tsk->thread.error_code = error_code;