[PATCH v4 49/57] x86/unwind: warn on kernel stack corruption

[Josh Poimboeuf]

Detect situations in the unwinder where the frame pointer refers to a
bad address, and print an appropriate warning.

Use printk_deferred_once() because the unwinder can be called with the
console lock by lockdep via save_stack_trace().

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 arch/x86/kernel/unwind_frame.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 2e729bf..65c5e416 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -130,8 +130,17 @@ bool unwind_next_frame(struct unwind_state *state)
 	}
 
 	/* make sure the next frame's data is accessible */
-	if (!update_stack_state(state, next_frame, next_len))
-		return false;
+	if (!update_stack_state(state, next_frame, next_len)) {
+		/*
+		 * Don't warn on bad regs->bp.  An interrupt in entry code
+		 * might cause a false positive warning.
+		 */
+		if (state->regs)
+			goto the_end;
+
+		goto bad_address;
+	}
+
 	/* move to the next frame */
 	if (regs) {
 		state->regs = regs;
@@ -143,6 +152,17 @@ bool unwind_next_frame(struct unwind_state *state)
 
 	return true;
 
+bad_address:
+	if (state->regs)
+		printk_deferred_once(KERN_WARNING
+			"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
+			state->regs, state->task->comm,
+			state->task->pid, next_bp);
+	else
+		printk_deferred_once(KERN_WARNING
+			"WARNING: kernel stack frame pointer at %p in %s:%d has bad value %p\n",
+			state->bp, state->task->comm,
+			state->task->pid, next_bp);
 the_end:
 	state->stack_info.type = STACK_TYPE_UNKNOWN;
 	return false;
-- 
2.7.4