[PATCH] avoid crashes due to unaligned stacks

This fixes the stack end detection properly, and verifies that the
stack content printing does not overflow into the next page even
partially.

This is required especially for x86 BIOSes that misalign the stack,
together with the page access debugging that unmaps unused kernel
pages to check for valid accesses.

Architectures with special needs (eg HPPA with stacks that grow up)
can override the kernel stack end test with __HAVE_ARCH_KSTACK_END
if they ever enable the anal slab debugging code.

arch/i386/kernel/traps.c

@@ -104,7 +104,7 @@ void show_trace(struct task_struct *task, unsigned long * stack)
 #ifdef CONFIG_KALLSYMS
 	printk("\n");
 #endif
-	while (((long) stack & (THREAD_SIZE-4)) != 0) {
+	while (!kstack_end(stack)) {
 		addr = *stack++;
 		if (kernel_text_address(addr)) {
 			printk(" [<%08lx>] ", addr);
@@ -138,7 +138,7 @@ void show_stack(struct task_struct *task, unsigned long *esp)
 
 	stack = esp;
 	for(i = 0; i < kstack_depth_to_print; i++) {
-		if (((long) stack & (THREAD_SIZE-4)) == 0)
+		if (kstack_end(stack))
 			break;
 		if (i && ((i % 8) == 0))
 			printk("\n       ");

include/linux/sched.h

@@ -541,6 +541,16 @@ union thread_union {
 	unsigned long stack[INIT_THREAD_SIZE/sizeof(long)];
 };
 
+#ifndef __HAVE_ARCH_KSTACK_END
+static inline int kstack_end(void *addr)
+{
+	/* Reliable end of stack detection:
+	 * Some APM bios versions misalign the stack
+	 */
+	return !(((unsigned long)addr+sizeof(void*)-1) & (THREAD_SIZE-sizeof(void*)));
+}
+#endif
+
 extern union thread_union init_thread_union;
 extern struct task_struct init_task;
 

mm/slab.c

@@ -862,7 +862,7 @@ static void store_stackinfo(kmem_cache_t *cachep, unsigned long *addr, unsigned
 		unsigned long *sptr = &caller;
 		unsigned long svalue;
 
-		while (((long) sptr & (THREAD_SIZE-4)) != 0) {
+		while (!kstack_end(sptr)) {
 			svalue = *sptr++;
 			if (kernel_text_address(svalue)) {
 				*addr++=svalue;