On Tue, Dec 17, 2024 at 09:27:44PM +0100, Benjamin Berg wrote: > From: Benjamin Berg <benjamin.berg@xxxxxxxxx> > > The init_task instance of struct task_struct is statically allocated and > does not contain the dynamic area for the userspace FP registers. 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 it. > > Reported-by: Brian Norris <briannorris@xxxxxxxxxxxx> > Closes: https://lore.kernel.org/Z1ySXmjZm-xOqk90@xxxxxxxxxx > Fixes: 3f17fed21491 ("um: switch to regset API and depend on XSTATE") No stable backport? The broken commit is now in the 6.13 release. > Signed-off-by: Benjamin Berg <benjamin.berg@xxxxxxxxx> Tested-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx> > --- > arch/um/kernel/process.c | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c > index 30bdc0a87dc8..3a67ba8aa62d 100644 > --- a/arch/um/kernel/process.c > +++ b/arch/um/kernel/process.c > @@ -191,7 +191,15 @@ void initial_thread_cb(void (*proc)(void *), void *arg) > 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 (missing 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); > + } Nitpick: This could make use of memcpy_and_pad() in various forms. > + > return 0; > } > > -- > 2.47.1 >
