x86/unwind: Warn on bad frame pointer

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@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/03c888f6f7414d54fa56b393ea25482be6899b5f.1477496147.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 579542736b7edbf6e00abfcbbfc4f4c95a1b5e1f..9be9a8f8c5dfeba9406b4a04cc50fc0f36fbae19 100644 (file)
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -123,8 +123,17 @@ 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;
@@ -136,6 +145,11 @@ bool unwind_next_frame(struct unwind_state *state)
 
        return true;
 
+bad_address:
+       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;