[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, 1 deletions

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index dad02a9..b0a0780 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -328,6 +328,7 @@ extern void kernel_thread_helper(void);
 int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 {
 	struct pt_regs regs;
+	int err;
 
 	memset(&regs, 0, sizeof(regs));
 
@@ -342,7 +343,10 @@ int kernel_thread(int (*fn)(void *), void * arg, unsigned long flags)
 	regs.eflags = X86_EFLAGS_IF | X86_EFLAGS_SF | X86_EFLAGS_PF | 0x2;
 
 	/* Ok, create the new process.. */
-	return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
+	err = do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
+	if (err == 0) /* terminate kernel stack */
+		task_pt_regs(current)->eip = 0;
+	return err;
 }
 EXPORT_SYMBOL(kernel_thread);