[PATCH] x86: Terminate the kernel stacks for the unwinder

Always make sure RIP/EIP is 0 in the registers stored on the top
of the stack of a kernel thread. This makes sure the unwinder code
won't try a fallback but knows the stack has ended.

AK: this patch is a bit mysterious. in theory they should be terminated
anyways, but it seems to fix at least one crash. Anyways double termination
probably doesn't hurt.

Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index b8285cf1a9c3..ab9b2c4726f2 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -978,6 +978,11 @@ ENTRY(kernel_thread)
         call do_fork
         movq %rax,RAX(%rsp)
         xorl %edi,%edi
+        test %rax,%rax
+        jnz  1f
+        /* terminate stack in child */
+        movq %rdi,RIP(%rsp)
+1:
 
         /*
          * It isn't worth to check for reschedule here,