Re: [PATCH v2 5/6] x86: Pass kernel thread parameters in fork_frame

[Brian Gerst]

On Sun, Jun 19, 2016 at 5:28 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Sat, Jun 18, 2016 at 1:56 PM, Brian Gerst <brgerst@xxxxxxxxx> wrote:
>> Instead of setting up a fake pt_regs context, put the kernel thread
>> function pointer and arg into the unused callee-restored registers
>> of struct fork_frame.
>
> This seems generally okay.
>
>>
>> Signed-off-by: Brian Gerst <brgerst@xxxxxxxxx>
>
>> @@ -146,19 +147,12 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
>
>
>>         if (unlikely(p->flags & PF_KTHREAD)) {
>>                 /* kernel thread */
>>                 memset(childregs, 0, sizeof(struct pt_regs));
>> -               frame->ret_addr = (unsigned long) ret_from_kernel_thread;
>> -               task_user_gs(p) = __KERNEL_STACK_CANARY;
>> -               childregs->ds = __USER_DS;
>> -               childregs->es = __USER_DS;
>> -               childregs->fs = __KERNEL_PERCPU;
>
> Is the idea that do_execve promises to initialize all these fields to
> something sensible if the kernel thread in question tries to return to
> user mode?
>
> --Andy

Yes, do_execve() should be setting the full pt_regs.

--
Brian Gerst