[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>

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index dad02a960e03572046c2e9ced98186c64e7ca5a5..b0a07801d9df90abf71f923fa27e55269cacf319 100644 (file)
--- 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);
 

diff --git a/arch/x86_64/kernel/entry.S b/arch/x86_64/kernel/entry.S
index b8285cf1a9c3b2780bdd53c499047856d378195d..ab9b2c4726f231c27cbd5958cb373c6c224b38a0 100644 (file)
--- 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,