commit 51ec28e1b2cb267a09a0b8eac1ccf8d61b7268bf
author Andi Kleen <ak@suse.de> Thu Oct 05 18:47:22 2006 +0200
committer Andi Kleen <andi@basil.nowhere.org> Thu Oct 05 18:47:22 2006 +0200
tree 4686d439a49b98b98fc5048641ddfb50db3fbcd6
parent f015c6c4d733f68cbc1c5d231bb158abaa5c9606

[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>

arch/i386/kernel/process.c

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 @@
 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 @@
 	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);
 

arch/x86_64/kernel/entry.S

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index b8285cf..ab9b2c4 100644
--- a/arch/x86_64/kernel/entry.S
+++ b/arch/x86_64/kernel/entry.S
@@ -978,6 +978,11 @@
 	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,