* Benjamin Berg <benjamin@xxxxxxxxxxxxxxxx> wrote:
> From: Benjamin Berg <benjamin.berg@xxxxxxxxx>
>
> The init_task instance of struct task_struct is statically allocated and
> may not contain the full FP state for userspace. As such, limit the copy
> to the valid area of init_task and fill the rest with zero.
>
> Note that the FP state is only needed for userspace, and as such it is
> entirely reasonable for init_task to not contain parts of it.
>
> Signed-off-by: Benjamin Berg <benjamin.berg@xxxxxxxxx>
> Fixes: 5aaeb5c01c5b ("x86/fpu, sched: Introduce CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT and use it on x86")
> ---
> arch/x86/kernel/process.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index f63f8fd00a91..1be45fe70cad 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -92,7 +92,15 @@ EXPORT_PER_CPU_SYMBOL_GPL(__tss_limit_invalid);
> */
> int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> {
> - memcpy(dst, src, arch_task_struct_size);
> + /* init_task is not dynamically sized (incomplete FPU state) */
> + if (unlikely(src == &init_task)) {
> + memcpy(dst, src, sizeof(init_task));
> + memset((void *)dst + sizeof(init_task), 0,
> + arch_task_struct_size - sizeof(init_task));
> + } else {
> + memcpy(dst, src, arch_task_struct_size);
Note that this patch, while it still applies cleanly, crashes/hangs the
x86-64 defconfig kernel bootup in the early boot phase in a KVM guest
bootup.
Thanks,
Ingo
