x86/dumpstack: Add get_stack_info() interface

valid_stack_ptr() is buggy: it assumes that all stacks are of size
THREAD_SIZE, which is not true for exception stacks.  So the
walk_stack() callbacks will need to know the location of the beginning
of the stack as well as the end.

Another issue is that in general the various features of a stack (type,
size, next stack pointer, description string) are scattered around in
various places throughout the stack dump code.

Encapsulate all that information in a single place with a new stack_info
struct and a get_stack_info() interface.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/8164dd0db96b7e6a279fa17ae5e6dc375eecb4a9.1473905218.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 91 insertions, 78 deletions

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 904fb46d7d65..41813abc7380 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -28,76 +28,109 @@ static unsigned long exception_stack_sizes[N_EXCEPTION_STACKS] = {
 	[DEBUG_STACK - 1]			= DEBUG_STKSZ
 };
 
-static unsigned long *in_exception_stack(unsigned long stack, unsigned *usedp,
-					 char **idp)
+void stack_type_str(enum stack_type type, const char **begin, const char **end)
 {
-	unsigned long begin, end;
+	BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
+
+	switch (type) {
+	case STACK_TYPE_IRQ:
+		*begin = "IRQ";
+		*end   = "EOI";
+		break;
+	case STACK_TYPE_EXCEPTION ... STACK_TYPE_EXCEPTION_LAST:
+		*begin = exception_stack_names[type - STACK_TYPE_EXCEPTION];
+		*end   = "EOE";
+		break;
+	default:
+		*begin = NULL;
+		*end   = NULL;
+	}
+}
+
+static bool in_exception_stack(unsigned long *stack, struct stack_info *info,
+			       unsigned long *visit_mask)
+{
+	unsigned long *begin, *end;
+	struct pt_regs *regs;
 	unsigned k;
 
 	BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
 
 	for (k = 0; k < N_EXCEPTION_STACKS; k++) {
-		end   = raw_cpu_ptr(&orig_ist)->ist[k];
-		begin = end - exception_stack_sizes[k];
+		end   = (unsigned long *)raw_cpu_ptr(&orig_ist)->ist[k];
+		begin = end - (exception_stack_sizes[k] / sizeof(long));
+		regs  = (struct pt_regs *)end - 1;
 
 		if (stack < begin || stack >= end)
 			continue;
 
 		/*
-		 * Make sure we only iterate through an exception stack once.
-		 * If it comes up for the second time then there's something
-		 * wrong going on - just break and return NULL:
+		 * Make sure we don't iterate through an exception stack more
+		 * than once.  If it comes up a second time then there's
+		 * something wrong going on - just break out and report an
+		 * unknown stack type.
 		 */
-		if (*usedp & (1U << k))
+		if (*visit_mask & (1U << k))
 			break;
-		*usedp |= 1U << k;
+		*visit_mask |= 1U << k;
 
-		*idp = exception_stack_names[k];
-		return (unsigned long *)end;
+		info->type	= STACK_TYPE_EXCEPTION + k;
+		info->begin	= begin;
+		info->end	= end;
+		info->next_sp	= (unsigned long *)regs->sp;
+
+		return true;
 	}
 
-	return NULL;
+	return false;
 }
 
-static inline int
-in_irq_stack(unsigned long *stack, unsigned long *irq_stack,
-	     unsigned long *irq_stack_end)
+static bool in_irq_stack(unsigned long *stack, struct stack_info *info)
 {
-	return (stack >= irq_stack && stack < irq_stack_end);
-}
+	unsigned long *end   = (unsigned long *)this_cpu_read(irq_stack_ptr);
+	unsigned long *begin = end - (IRQ_STACK_SIZE / sizeof(long));
 
-enum stack_type {
-	STACK_IS_UNKNOWN,
-	STACK_IS_NORMAL,
-	STACK_IS_EXCEPTION,
-	STACK_IS_IRQ,
-};
+	if (stack < begin || stack >= end)
+		return false;
+
+	info->type	= STACK_TYPE_IRQ;
+	info->begin	= begin;
+	info->end	= end;
+
+	/*
+	 * The next stack pointer is the first thing pushed by the entry code
+	 * after switching to the irq stack.
+	 */
+	info->next_sp = (unsigned long *)*(end - 1);
+
+	return true;
+}
 
-static enum stack_type
-analyze_stack(struct task_struct *task, unsigned long *stack,
-	      unsigned long **stack_end, unsigned long *irq_stack,
-	      unsigned *used, char **id)
+int get_stack_info(unsigned long *stack, struct task_struct *task,
+		   struct stack_info *info, unsigned long *visit_mask)
 {
-	unsigned long addr;
+	if (!stack)
+		goto unknown;
 
-	addr = ((unsigned long)stack & (~(THREAD_SIZE - 1)));
-	if ((unsigned long)task_stack_page(task) == addr)
-		return STACK_IS_NORMAL;
+	task = task ? : current;
+
+	if (in_task_stack(stack, task, info))
+		return 0;
 
-	*stack_end = in_exception_stack((unsigned long)stack, used, id);
-	if (*stack_end)
-		return STACK_IS_EXCEPTION;
+	if (task != current)
+		goto unknown;
 
-	if (!irq_stack)
-		return STACK_IS_NORMAL;
+	if (in_exception_stack(stack, info, visit_mask))
+		return 0;
 
-	*stack_end = irq_stack;
-	irq_stack -= (IRQ_STACK_SIZE / sizeof(long));
+	if (in_irq_stack(stack, info))
+		return 0;
 
-	if (in_irq_stack(stack, irq_stack, *stack_end))
-		return STACK_IS_IRQ;
+	return 0;
 
-	return STACK_IS_UNKNOWN;
+unknown:
+	info->type = STACK_TYPE_UNKNOWN;
+	return -EINVAL;
 }
 
 /*
@@ -111,8 +144,8 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 		unsigned long *stack, unsigned long bp,
 		const struct stacktrace_ops *ops, void *data)
 {
-	unsigned long *irq_stack = (unsigned long *)this_cpu_read(irq_stack_ptr);
-	unsigned used = 0;
+	unsigned long visit_mask = 0;
+	struct stack_info info;
 	int graph = 0;
 	int done = 0;
 
@@ -126,57 +159,37 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 	 * exceptions
 	 */
 	while (!done) {
-		unsigned long *stack_end;
-		enum stack_type stype;
-		char *id;
+		const char *begin_str, *end_str;
 
-		stype = analyze_stack(task, stack, &stack_end, irq_stack, &used,
-				      &id);
+		get_stack_info(stack, task, &info, &visit_mask);
 
 		/* Default finish unless specified to continue */
 		done = 1;
 
-		switch (stype) {
+		switch (info.type) {
 
 		/* Break out early if we are on the thread stack */
-		case STACK_IS_NORMAL:
+		case STACK_TYPE_TASK:
 			break;
 
-		case STACK_IS_EXCEPTION:
+		case STACK_TYPE_IRQ:
+		case STACK_TYPE_EXCEPTION ... STACK_TYPE_EXCEPTION_LAST:
+
+			stack_type_str(info.type, &begin_str, &end_str);
 
-			if (ops->stack(data, id) < 0)
+			if (ops->stack(data, begin_str) < 0)
 				break;
 
 			bp = ops->walk_stack(task, stack, bp, ops,
-					     data, stack_end, &graph);
-			ops->stack(data, "EOE");
-			/*
-			 * We link to the next stack via the
-			 * second-to-last pointer (index -2 to end) in the
-			 * exception stack:
-			 */
-			stack = (unsigned long *) stack_end[-2];
-			done = 0;
-			break;
+					     data, &info, &graph);
 
-		case STACK_IS_IRQ:
+			ops->stack(data, end_str);
 
-			if (ops->stack(data, "IRQ") < 0)
-				break;
-			bp = ops->walk_stack(task, stack, bp,
-				     ops, data, stack_end, &graph);
-			/*
-			 * We link to the next stack (which would be
-			 * the process stack normally) the last
-			 * pointer (index -1 to end) in the IRQ stack:
-			 */
-			stack = (unsigned long *) (stack_end[-1]);
-			irq_stack = NULL;
-			ops->stack(data, "EOI");
+			stack = info.next_sp;
 			done = 0;
 			break;
 
-		case STACK_IS_UNKNOWN:
+		default:
 			ops->stack(data, "UNK");
 			break;
 		}
@@ -185,7 +198,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
 	/*
 	 * This handles the process stack:
 	 */
-	bp = ops->walk_stack(task, stack, bp, ops, data, NULL, &graph);
+	bp = ops->walk_stack(task, stack, bp, ops, data, &info, &graph);
 }
 EXPORT_SYMBOL(dump_trace);